1 Department of Electrical Engineering Chonnam National University Gwangju 500-757 Republic of Korea2The Research Institute of Advanced Engineering Technology Chosun University Gwangju 501-759 Republic of Korea3 Southwestern Research Institute of Green Energy Mokpo 530-400 Republic of Korea4Department of Chemical and Biochemical Engineering Chosun University Gwangju 590-170 Republic of Korea5 Gist Technology Institute Gwangju Institute of Science and Technology Gwangju 500-712 Republic of Korea6Department of Environmental Engineering Chonnam National University Gwangju 500-757 Republic of Korea7 School of Materials Science amp Engineering Chonnam National University Gwangju 500-757 Republic of Korea
Correspondence should be addressed to Tae-Young Kim tykim001chonnamackr
Received 21 May 2013 Revised 3 August 2013 Accepted 1 September 2013
Academic Editor Mark van Der Auweraer
Copyright copy 2013 En Mei Jin et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
A chitosan binder-based TiO2photoelectrode is used in dye-sensitized solar cells (DSSCs) Field-emission scanning electron
microscope (FE-SEM) images revealed that the grain size thickness and distribution of TiO2films are affected by the chitosan
content With addition of 20 wt chitosan to the TiO2film (D2) the surface pore size became the smallest and the pores were
fairly evenly distributedThe electron transit time electron recombination lifetime diffusion coefficient and diffusion length wereanalyzed by IMVS and IMPS The best DSSC with 20 wt chitosan addition to the TiO
2film had a shorter electron transit time
longer electron recombination lifetime and larger diffusion coefficient and diffusion length than the other samples The results of20 wt chitosan-added TiO
2DSSCs are an electron transit time of 2189times10minus3 s electron recombination lifetime of 6336times10minus2 s
diffusion coefficient of 3463 times 10minus5 cm2 sminus1 diffusion length of 1481120583m and a solar conversion efficiency of 418
1 IntroductionSince the Gratzel group discovered dye-sensitized solar cells(DSSCs) many researchers have become interested in them[1ndash5] The low-cost high-solar conversion efficiency ofDSSCs is considered as a possible alternative to contemporarysilicon solar cells [6 7] DSSCs are basically a thin layersolar cell formed by the sandwich arrangement of twoelectrodes that is a photoelectrode which is a few micronthick mesoporous TiO
2layer coated with photosensitizer
and a platinum (Pt) coated counter electrode The interlayerspace is filled with a soluble redox couple electrolyte suchas IminusI
3
minus [8ndash11] TiO2is chemically stable nontoxic and
readily available in vast quantities DSSCs have many com-ponents that have to be optimized the mesoporous TiO
2
layer is very important for increasing the solar conversionefficiency among others [12ndash18] So far the TiO
2-based
DSSCs fabricated using multilayer (about 14120583m thickness)approaches have shown a solar conversion efficiency of113 which is lower than the theoretical maximum (33)[19 20] Many researchers in order to increase the solarconversion efficiency in DSSCs have studied improvementsto the photoelectrodes such as the synthesis of wide band-gap TiO
2 small particle size of 10 to approximately 20 nm
large surface area of TiO2 and increased porosity These can
increase the adsorption of the dye and by extension the solarconversion efficiency could be increased [21 22]
In this present research chitosan was adopted as anew electrode binder for DSSCs Chitosan is a polysaccha-ride composedmainly of120573-(14)-linked 2-deoxy-2-amino-D-glucopyranose units Chitosan can be considered the mostenvironment-friendly binder and chitosan-based aqueousslurries possesses good viscosity and so can be considered
2 International Journal of Photoenergy
Table 1 Composition of the as-prepared chitosan sol-based TiO2pastes used in this study
as an effective electrode binder We investigate natural chi-tosan binder-based DSSCs describing the effect of differentcontents of chitosan on the activity of DSSCsWe selected forour research four amounts of 15 wt 20 wt 25 wt and30 wt of chitosan content in the TiO
2electrode named as
D1 D2 D3 and D4 respectively
2 Experiment
21 Preparation of Chitosan Sol and TiO2Paste The chitosan
used in this study was kindly supplied by Sehwa Co KoreaThe degree of deacetylation and molecular weight of thechitosan were 85 and 52 times 105 gmol respectively Chitosansol with different concentrations (15 20 25 and 30 wt)were prepared by dissolving the proper amount of chitosan in2mL of 3 (vv) aqueous acetic acid solution The solutionwas mixed using a shaking incubator for 24 h at 250 rpmand then the solution was left to stand for 24 h at roomtemperature for complete hydration of the polymer andremoval of bubbles
The chitosan-based TiO2paste was prepared in the
followingway nitric acid treated TiO2(P-25 Deagesa) power
was added to 2mL of prepared chitosan colloidal solutionand then stirring was maintained until the TiO
2colloid was
well mixed with the chitosan solution slurry For increaseddispersal of the TiO
2paste a three-roll mill (DEA WHA
TECH EXAKT50i) was used for about 7 h The three-rollmill makes it possible to simultaneously mill and mix thepaste Table 1 shows the composition of chitosan sol-basedTiO2pastes of D1 D2 D3 and D4 used in this study
22 Preparation of the Photo and Counter Electrode Theprepared TiO
2paste was cast on precleaned FTO (Pilkington
FTO glass 8Ωcm2) using the squeeze printing method[3 23ndash25] The coated TiO
2films were sintered at 150∘C for
3 h The active area of the TiO2film was 025 cm2 The TiO
2
film was immersed into a 5 times 10minus4molL ethanol solutionof Ru(dcbpy)
2(NCS)
2(N719 Solaronix Co Switzerland)
overnight then rinsed with anhydrous ethanol and finallydried The counter electrode was prepared using the squeezeprinting technique and subsequently sintered at 450∘C for30min The counter electrode material was a Pt catalyst(Solaronix Co Switzerland)
23 Assembly of the Testing Cells The Pt electrode was pla-ced over the dye-adsorbed TiO
2electrode and the edges
of the cell were sealed The sealing was accomplished byhot-pressing two electrodes together at 110∘C The redox
0 100 200 300 400 500 600
Wei
ght l
oss (
)
0
20
40
60
80
100
minus20
Only chitosan binderD2
Temperature (∘C)
Figure 1 Thermal weight loss (TGA) curve of the pure chitosan sol(20) and chitosan sol-based TiO
2paste (D2)
electrolyte was injected into the cell through two smallholes drilled in the counter electrode The IminusI
3
minus redox elec-trolyte was composed of 03molL 12-dimethyl-3-propylimi-dazolium iodide (Sigma-Aldrich Co USA) 05molL 4-tert-butylpyridine (Sigma-Aldrich Co USA) and 3-metoxypro-pionitrile The holes were then covered and sealed with asmall square of sealing material and a microscope objectiveglass
24 Measurements The thermogravimetric (TGA) analysesof the chitosan sol were performed with an RIS diamond TG-DTA (PerkinElmer) analyzer The chitosan sol was loadedinto alumina pans and heated from room temperature to530∘C
Field-emission scanning electron microscopy (FE-SEM)(Hitachi S-4700 Japan) was used to examine the film mor-phology such as the surface of TiO
2films and thickness
The electron transit time and electron recombinationlifetime were measured by intensity modulated photocurrentspectroscopy (IMPS) and intensity modulated photovoltagespectroscopy (IMVS) Blue light-emitting diodes (LEDs475 nm) were used as the light source The light intensitieswere modulated (10) by modulating the bias applied to theLED with sine waves in a frequency range typically from01Hz to 1000Hz
The photovoltaic properties were investigated by measur-ing the photocurrent-voltage characteristics under illumina-tion with an air mass (AM) of 15 (100mWcm2) simulatedsunlight The charge transport characteristics were inves-tigated by intensity-modulated photovoltage spectroscopy(IMVS) The IMVS was measured using red light-emittingdiodes (LED 635 nm) The light intensities were modulatedby 10 in a frequency range typically from 001 to 100Hz
3 Results and DiscussionThe thermal weight loss curves for the pure chitosan sol(20 wt) and chitosan sol-based TiO
2paste (D2) are shown
International Journal of Photoenergy 3
D1
(a)
D2
(b)
D3
(c)
D4
(d)Figure 2 FE-SEM images of the surface morphologies of chitosan sol-based TiO
2films
in Figure 1 This shows that there is a large weight loss in therange from room temperature to 80∘C in the TG curve whichis due to the dehydration of the pure chitosan sol and chitosansol-based TiO
2paste This weight loss can be assigned to the
thermal decomposition of aqueous acetic acid in the purechitosan sol As shown in the TGA curve of D2 we can verifythat about 20wt residue is accurate and the residue canbe ascribed to the TiO
2powder So the heating temperature
of the TiO2photoelectrode (after TiO
2casting on the FTO
substrate) can be set to be very lowThe surface morphologies of the pure TiO
2photoelec-
trode and TiO2photoelectrode containing 15 wt (D1)
20 wt (D2) 25 wt (D3) and 30 wt (D4) of chitosanwere obtained by FE-SEM and are depicted in Figure 2 Ascan be seen in Figure 2 the TiO
2pastes containing different
weight of chitosan could result in the TiO2films having
different distributions of pore diameters It was found that theTiO2film prepared with the D2 paste shows a smaller pore
structure and that prepared with D1 D3 and D4 pastes has alarger pore diameter The penetration of electrolyte dependson the pore size and porosity of the TiO
2film [26] We will
investigate the influence on lifetime of the TiO2electrode as
well as the performance of the DSSC by varying the amountsof chitosan content in the TiO
2electrode
Figure 3 shows FE-SEM images of the cross-section ofchitosan sol-based TiO
2films In this figure the thickness of
TiO2ofD1 D2 D3 andD4 is 68 69 68 and 66 120583m respec-
tively The solar conversion efficiency of DSSCs dependsupon several factors including the porosity surface area andamount of dye loading [26]
Table 2 Photocurrent-voltage data of the chitosan sol-basedDSSCs
Figure 4 shows the photocurrent-voltage characteristicsof different chitosan-based DSSCs The solar cell was irra-diated with a 1000W xenon lamp with a light intensity of100mA cmminus2 as a light source As shown in Figure 4 theD2-based DSSC has a higher solar current density than theD1 D3 and D4-based DSSCs Table 2 shows the data of thephotocurrent-voltage characteristicsTheopen circuit voltage(119881oc) short-circuit current density (119869sc) fill factor (FF) andthe solar energy conversion efficiency (120578) of the D2-basedDSSC are 069V 1015mA cmminus2 5941 and 418 respec-tivelyThe 120578 of D1 D3 and D4-based DSSCs are 38 395327 respectively Gratzel and coworkers have reported ona highly efficient (7ndash11) photoelectrochemical cell basedon sensitized oxidation of iodide on a nanocrystalline TiO
2
electrode using an artificial binder [27 28] However we usednatural binder (chitosan) for TiO
2paste In comparison to the
artificial binder the efficiency of DSSCs using natural binderis not high However there is little data available on the useof natural binder for TiO
2paste in the literature Yang et al
4 International Journal of Photoenergy
68 120583m
D1
(a)
69 120583m
D2
(b)
68 120583m
D3
(c)
66 120583m
D4
(d)Figure 3 FE-SEM images of the cross-section of chitosan sol-based TiO
2films
Voltage (V)
00 01 02 03 04 05 06 070
2
4
6
8
10
12
D1D2
D3D4
Curr
ent d
ensit
y (m
Ac
m2)
Figure 4 Photocurrent-voltage curves of chitosan sol-basedDSSCs
[29] reported on a DSSC with a novel Pt counter electrodesusing pulsed electroplating techniques the efficiency ofDSSC was 385 Deepa et al [30] reported on efficiency
enhancement in DSSCs using metal nanoparticles a size-dependent study the efficiency of DSSCs range from 043 to152 Compared to the research of Yang et al and Deepa et althe efficiency of DSSCs using natural binder is highTheTiO
2
photoelectrode morphology can also influence photocurrentgeneration The higher efficiency of photocurrent generationhas been explained by a reduction in grain boundarieshigher dye loadings and slower recombination rates [31ndash35] The electron recombination lifetimes within DSSCs aredetermined primarily by the recombination of electrons withiodine electrolyte and oxidized sensitizers To understandthe charge transport characteristics the films were investi-gated by IMPS and IMVS The electron transit time (120591
119905) and
electron recombination time (120591119903) can be determined using
the equations 120591119905= 12120587119891min and 120591
119903= 12120587119891min1015840 In the
equations119891min and119891min1015840 are the frequencies giving the largestimaginary components in IMPS and IMVS respectively TheIMPS and IMVS plots are shown in Figure 5 Figure 6displays the diffusion coefficient of chitosan-based DSSCsand Table 3 shows the electron transport characteristic dataThe electron transit time of D1 D2 D3 and D4-based DSSCsis 3121 times 10minus3 2189 times 10minus3 2295 times 10minus3 and 4056 times10minus3 sminus1 respectively The electron recombination lifetimeof the D2-based DSSC was lower than those of the othersamples For the D2-based DSSC the recombination lifetimeis 6336 times 10minus2 s This result clearly indicates that electronrecombination with the oxidized species is reduced in theD2 TiO
2film This can be understood by either looking
at improvements in the network of TiO2nanoparticles or
at the electron behavior during transition in the D2-based
International Journal of Photoenergy 5
0 2 4 6 8 10 120
1
2
3
4
5
6
7
8
D1D2
D3D4
Z998400998400
(Wtimes
10minus4)
Z998400 (W times10minus4)minus2
(a)
D1D2
D3D4
0 1 2 3 4 500
05
10
15
20
25
30
Z998400998400
(Ωtimes
103)
Z998400 (Ω times103)
(b)Figure 5 Intensity modulation photocurrent spectroscopy (IMPS) and intensity modulation photovoltage spectroscopy (IMVS) of chitosansol-based DSSCs
Table 3 Charge transport parameter of the chitosan sol-basedDSSCs
TiO2film From the FE-SEM I-V and electron transport
characteristic results the D2-based DSSCs have a very goodfilm surface uniformity and high porosity Consequentlythe D2-based DSSCs have increased surface absorption andenhanced solar energy conversion efficiency
4 Conclusions
DSSCs were fabricated using different chitosan binder sol(15sim30 wt)-based photoelectrodesThe chitosan binder solhad low calcination temperature (sim150∘C) and successfullyprepared low temperature TiO
2photoelectrodes The D2
(sim20 wt)-based DSSCs had faster electron transit time andslower electron recombination time than the other samples(D1 D3 and D4) The D2-based DSSC exhibited highersolar conversion efficiencies than D1 D3 and D4-basedDSSCs because the electron recombination is more than 15sim3 times slower in the D2-based DSSC The electron diffusioncoefficient of the D2-based DSSC was 3463times 10minus5 cm2 sminus1
05 06 07 08 09 11
2
3
4
D1D2
D3D4
Voltage (V)
Diff
usio
n co
effici
ent (
cm2
sminus1times
10minus5)
Figure 6 Diffusion coefficient of chitosan sol-based DSSCs
and the diffusion length was 1481 120583m The efficiency ofthe D2 based DSSC was optimized to achieve 416 underillumination of simulated solar light AM 15 global (119881oc =069 V 119869sc = 1016mAcmminus2 fill factor is 5941)
Acknowledgment
This research was supported by Specialized Local IndustryDevelopment Program through Korea Institute for Advance-ment of Technology (KIAT) funded by theMinistry of Trade
6 International Journal of Photoenergy
Industry and Energy (1415127923-R0002040) And the BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation Science and Technology (2012010655)
References
[1] I J Kramer A G Pattantyus-Abraham A R Barkhouse et alldquoRETRACTED advances in colloidal quantum dot solar cellsthe depleted-heterojunction devicerdquo Thin Solid Films vol 519no 21 pp 7351ndash7355 2011
[2] D Kuang P Comte S M Zakeeruddin et al ldquoStable dye-sensitized solar cells based on organic chromophores and ionicliquid electrolyterdquo Solar Energy vol 85 no 6 pp 1189ndash11942011
[3] I KDing JMelas-Kyriazi N L Cevey-Ha et al ldquoDeposition ofhole-transport materials in solid-state dye-sensitized solar cellsby doctor-bladingrdquo Organic Electronics vol 11 no 7 pp 1217ndash1222 2010
[4] J H Yum S J Moon C S Karthikeyan et al ldquoHeterolep-tic ruthenium complex containing substituted triphenylaminehole-transport unit as sensitizer for stable dye-sensitized solarcellrdquo Nano Energy vol 1 no 1 pp 6ndash12 2012
[5] G Calogero J H Yum A Sinopoli G D Marco M Gratzeland M K Nazeeruddin ldquoAnthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cellsrdquo Solar Energyvol 86 no 5 pp 1563ndash1575 2012
[6] B OrsquoRegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO
2filmsrdquo Nature vol
353 no 6346 pp 737ndash740 1991[7] H Lindstrom A Holmberg E Magnusson L Malmqvist
and A Hagfeldt ldquoA new method to make dye-sensitizednanocrystalline solar cells at room temperaturerdquo Journal ofPhotochemistry and Photobiology A vol 145 no 1-2 pp 107ndash1122001
[8] B Tan and Y Wu ldquoDye-sensitized solar cells based on anataseTiO2nanoparticlenanowire compositesrdquo Journal of Physical
Chemistry B vol 110 no 32 pp 15932ndash15938 2006[9] E M Jin K H Park J J Yun et al ldquoPhotovoltaic properties
of TiO2photoelectrode prepared by using liquid PEG-EEM
binderrdquo Surface Review and Letters vol 17 no 1 pp 15ndash20 2010[10] K H Park H B Gu E M Jin and M Dhayal ldquoUsing hybrid
silica-conjugated TiO2nanostructures to enhance the efficiency
of dye-sensitized solar cellsrdquo Electrochimica Acta vol 55 no 19pp 5499ndash5505 2010
[11] S Hore C Vetter R Kern H Smit and A Hinsch ldquoInfluenceof scattering layers on efficiency of dye-sensitized solar cellsrdquoSolar Energy Materials and Solar Cells vol 90 no 9 pp 1176ndash1188 2006
[12] H Pettersson T Gruszecki L Johansson M O M EdwardsA Hagfeldt and T Matuszczyk ldquoDirect-driven electrochromicdisplays based on nanocrystalline electrodesrdquo Displays vol 25no 5 pp 223ndash230 2004
[13] E L Tae S H Lee J K Lee S S Yoo E J Kang andK B YoonldquoA strategy to increase the efficiency of the dye-sensitized TiO
2
solar cells operated by photoexcitation of dye-to-TiO2charge-
transfer bandsrdquo Journal of Physical Chemistry B vol 109 no 47pp 22513ndash22522 2005
[14] J Y Lin T J Chen and C K Hu ldquoEffects of anodic titaniumoxide nanotube arrays on dye-sensitized solar cellsrdquo Journal ofthe Chinese Chemical Society vol 57 no 5 pp 1176ndash1179 2010
[15] K Nelson and Y Deng ldquoEffect of polycrystalline structureof TiO
2particles on the light scattering efficiencyrdquo Journal of
Colloid and Interface Science vol 319 no 1 pp 130ndash139 2008[16] C S Chou R Y Yang C K Yeh and Y J Lin ldquoPreparation of
TiO2nano-metal composite particles and their applications in
dye-sensitized solar cellsrdquo Powder Technology vol 194 no 1-2pp 95ndash105 2009
[17] M C Kao H Z Chen S L Young C Y Kung and C C LinldquoThe effects of the thickness of TiO
2films on the performance
of dye-sensitized solar cellsrdquoThin Solid Films vol 517 no 17 pp5096ndash5099 2009
[18] F Odobel Y Pellegrin E A Gibson A Hagfeldt A L Smeighand L Hammarstrom ldquoRecent advances and future directionsto optimize the performances of p-type dye-sensitized solarcellsrdquo Coordination Chemistry Reviews vol 256 no 21-22 pp2414ndash2423 2012
[19] N Fuke A Fukui A Islam et al ldquoInfluence of TiO2electrode
interface on electron transport properties in back contact dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol93 no 6-7 pp 720ndash724 2009
[20] C Xu P H Shin L Cao J Wu and D Gao ldquoOrderedTiO2nanotube arrays on transparent conductive oxide for dye-
sensitized solar cellsrdquo Chemistry of Materials vol 22 no 1 pp143ndash148 2010
[21] Y B Tang C S Lee J Xu et al ldquoIncorporation of graphenesin nanostructured TiO
2films via molecular grafting for dye-
sensitized solar cell applicationrdquo ACS Nano vol 4 no 6 pp3482ndash3488 2010
[22] A S Nair R Jose Y Shengyuan and S Ramakrishna ldquoA simplerecipe for an efficient TiO
2nanofiber-based dye-sensitized solar
cellrdquo Journal of Colloid and Interface Science vol 353 no 1 pp39ndash45 2011
[23] A I Kontos A G Kontos D S Tsoukleris M Bernard NSpyrellis and P Falaras ldquoNanostructured TiO
2films for DSSCS
prepared by combining doctor-blade and sol-gel techniquesrdquoJournal of Materials Processing Technology vol 196 no 1ndash3 pp243ndash248 2008
[24] I Bernacka-Wojcik R Senadeera P J Wojcik et al ldquoInkjetprinted and ldquodoctor bladerdquo TiO
2photodetectors for DNA bio-
sensorsrdquo Biosensors and Bioelectronics vol 25 no 5 pp 1229ndash1234 2010
[25] N Nang Dinh N Minh Quyen D N Chung M Zikova andV V Truong ldquoHighly-efficient electrochromic performance ofnanostructured TiO 2 films made by doctor blade techniquerdquoSolar Energy Materials and Solar Cells vol 95 no 2 pp 618ndash623 2011
[26] Y Saito S Kambe T Kitamura Y Wada and S YanagidaldquoMorphology control of mesoporous TiO
2nanocrystalline
films for performance of dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol 83 no 1 pp 1ndash13 2004
[27] M Gratzel ldquoPhotovoltaic performance and long-term stabilityof dye-sensitized meosocopic solar cellsrdquo Comptes RendusChimie vol 9 no 5-6 pp 578ndash583 2006
[28] D Kuang C Klein H J Snaith R Humphry-Baker SM Zakeeruddin and M Gratzel ldquoA new ion-coordinatingruthenium sensitizer for mesoscopic dye-sensitized solar cellsrdquoInorganica Chimica Acta vol 361 no 3 pp 699ndash706 2008
[29] C C Yang H Q Zhang and Y R Zheng ldquoDSSC with a novelPt counter electrodes using pulsed electroplating techniquesrdquoCurrent Applied Physics vol 11 no 1 supplement pp S147ndashS1532011
International Journal of Photoenergy 7
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
as an effective electrode binder We investigate natural chi-tosan binder-based DSSCs describing the effect of differentcontents of chitosan on the activity of DSSCsWe selected forour research four amounts of 15 wt 20 wt 25 wt and30 wt of chitosan content in the TiO
2electrode named as
D1 D2 D3 and D4 respectively
2 Experiment
21 Preparation of Chitosan Sol and TiO2Paste The chitosan
used in this study was kindly supplied by Sehwa Co KoreaThe degree of deacetylation and molecular weight of thechitosan were 85 and 52 times 105 gmol respectively Chitosansol with different concentrations (15 20 25 and 30 wt)were prepared by dissolving the proper amount of chitosan in2mL of 3 (vv) aqueous acetic acid solution The solutionwas mixed using a shaking incubator for 24 h at 250 rpmand then the solution was left to stand for 24 h at roomtemperature for complete hydration of the polymer andremoval of bubbles
The chitosan-based TiO2paste was prepared in the
followingway nitric acid treated TiO2(P-25 Deagesa) power
was added to 2mL of prepared chitosan colloidal solutionand then stirring was maintained until the TiO
2colloid was
well mixed with the chitosan solution slurry For increaseddispersal of the TiO
2paste a three-roll mill (DEA WHA
TECH EXAKT50i) was used for about 7 h The three-rollmill makes it possible to simultaneously mill and mix thepaste Table 1 shows the composition of chitosan sol-basedTiO2pastes of D1 D2 D3 and D4 used in this study
22 Preparation of the Photo and Counter Electrode Theprepared TiO
2paste was cast on precleaned FTO (Pilkington
FTO glass 8Ωcm2) using the squeeze printing method[3 23ndash25] The coated TiO
2films were sintered at 150∘C for
3 h The active area of the TiO2film was 025 cm2 The TiO
2
film was immersed into a 5 times 10minus4molL ethanol solutionof Ru(dcbpy)
2(NCS)
2(N719 Solaronix Co Switzerland)
overnight then rinsed with anhydrous ethanol and finallydried The counter electrode was prepared using the squeezeprinting technique and subsequently sintered at 450∘C for30min The counter electrode material was a Pt catalyst(Solaronix Co Switzerland)
23 Assembly of the Testing Cells The Pt electrode was pla-ced over the dye-adsorbed TiO
2electrode and the edges
of the cell were sealed The sealing was accomplished byhot-pressing two electrodes together at 110∘C The redox
0 100 200 300 400 500 600
Wei
ght l
oss (
)
0
20
40
60
80
100
minus20
Only chitosan binderD2
Temperature (∘C)
Figure 1 Thermal weight loss (TGA) curve of the pure chitosan sol(20) and chitosan sol-based TiO
2paste (D2)
electrolyte was injected into the cell through two smallholes drilled in the counter electrode The IminusI
3
minus redox elec-trolyte was composed of 03molL 12-dimethyl-3-propylimi-dazolium iodide (Sigma-Aldrich Co USA) 05molL 4-tert-butylpyridine (Sigma-Aldrich Co USA) and 3-metoxypro-pionitrile The holes were then covered and sealed with asmall square of sealing material and a microscope objectiveglass
24 Measurements The thermogravimetric (TGA) analysesof the chitosan sol were performed with an RIS diamond TG-DTA (PerkinElmer) analyzer The chitosan sol was loadedinto alumina pans and heated from room temperature to530∘C
Field-emission scanning electron microscopy (FE-SEM)(Hitachi S-4700 Japan) was used to examine the film mor-phology such as the surface of TiO
2films and thickness
The electron transit time and electron recombinationlifetime were measured by intensity modulated photocurrentspectroscopy (IMPS) and intensity modulated photovoltagespectroscopy (IMVS) Blue light-emitting diodes (LEDs475 nm) were used as the light source The light intensitieswere modulated (10) by modulating the bias applied to theLED with sine waves in a frequency range typically from01Hz to 1000Hz
The photovoltaic properties were investigated by measur-ing the photocurrent-voltage characteristics under illumina-tion with an air mass (AM) of 15 (100mWcm2) simulatedsunlight The charge transport characteristics were inves-tigated by intensity-modulated photovoltage spectroscopy(IMVS) The IMVS was measured using red light-emittingdiodes (LED 635 nm) The light intensities were modulatedby 10 in a frequency range typically from 001 to 100Hz
3 Results and DiscussionThe thermal weight loss curves for the pure chitosan sol(20 wt) and chitosan sol-based TiO
2paste (D2) are shown
International Journal of Photoenergy 3
D1
(a)
D2
(b)
D3
(c)
D4
(d)Figure 2 FE-SEM images of the surface morphologies of chitosan sol-based TiO
2films
in Figure 1 This shows that there is a large weight loss in therange from room temperature to 80∘C in the TG curve whichis due to the dehydration of the pure chitosan sol and chitosansol-based TiO
2paste This weight loss can be assigned to the
thermal decomposition of aqueous acetic acid in the purechitosan sol As shown in the TGA curve of D2 we can verifythat about 20wt residue is accurate and the residue canbe ascribed to the TiO
2powder So the heating temperature
of the TiO2photoelectrode (after TiO
2casting on the FTO
substrate) can be set to be very lowThe surface morphologies of the pure TiO
2photoelec-
trode and TiO2photoelectrode containing 15 wt (D1)
20 wt (D2) 25 wt (D3) and 30 wt (D4) of chitosanwere obtained by FE-SEM and are depicted in Figure 2 Ascan be seen in Figure 2 the TiO
2pastes containing different
weight of chitosan could result in the TiO2films having
different distributions of pore diameters It was found that theTiO2film prepared with the D2 paste shows a smaller pore
structure and that prepared with D1 D3 and D4 pastes has alarger pore diameter The penetration of electrolyte dependson the pore size and porosity of the TiO
2film [26] We will
investigate the influence on lifetime of the TiO2electrode as
well as the performance of the DSSC by varying the amountsof chitosan content in the TiO
2electrode
Figure 3 shows FE-SEM images of the cross-section ofchitosan sol-based TiO
2films In this figure the thickness of
TiO2ofD1 D2 D3 andD4 is 68 69 68 and 66 120583m respec-
tively The solar conversion efficiency of DSSCs dependsupon several factors including the porosity surface area andamount of dye loading [26]
Table 2 Photocurrent-voltage data of the chitosan sol-basedDSSCs
Figure 4 shows the photocurrent-voltage characteristicsof different chitosan-based DSSCs The solar cell was irra-diated with a 1000W xenon lamp with a light intensity of100mA cmminus2 as a light source As shown in Figure 4 theD2-based DSSC has a higher solar current density than theD1 D3 and D4-based DSSCs Table 2 shows the data of thephotocurrent-voltage characteristicsTheopen circuit voltage(119881oc) short-circuit current density (119869sc) fill factor (FF) andthe solar energy conversion efficiency (120578) of the D2-basedDSSC are 069V 1015mA cmminus2 5941 and 418 respec-tivelyThe 120578 of D1 D3 and D4-based DSSCs are 38 395327 respectively Gratzel and coworkers have reported ona highly efficient (7ndash11) photoelectrochemical cell basedon sensitized oxidation of iodide on a nanocrystalline TiO
2
electrode using an artificial binder [27 28] However we usednatural binder (chitosan) for TiO
2paste In comparison to the
artificial binder the efficiency of DSSCs using natural binderis not high However there is little data available on the useof natural binder for TiO
2paste in the literature Yang et al
4 International Journal of Photoenergy
68 120583m
D1
(a)
69 120583m
D2
(b)
68 120583m
D3
(c)
66 120583m
D4
(d)Figure 3 FE-SEM images of the cross-section of chitosan sol-based TiO
2films
Voltage (V)
00 01 02 03 04 05 06 070
2
4
6
8
10
12
D1D2
D3D4
Curr
ent d
ensit
y (m
Ac
m2)
Figure 4 Photocurrent-voltage curves of chitosan sol-basedDSSCs
[29] reported on a DSSC with a novel Pt counter electrodesusing pulsed electroplating techniques the efficiency ofDSSC was 385 Deepa et al [30] reported on efficiency
enhancement in DSSCs using metal nanoparticles a size-dependent study the efficiency of DSSCs range from 043 to152 Compared to the research of Yang et al and Deepa et althe efficiency of DSSCs using natural binder is highTheTiO
2
photoelectrode morphology can also influence photocurrentgeneration The higher efficiency of photocurrent generationhas been explained by a reduction in grain boundarieshigher dye loadings and slower recombination rates [31ndash35] The electron recombination lifetimes within DSSCs aredetermined primarily by the recombination of electrons withiodine electrolyte and oxidized sensitizers To understandthe charge transport characteristics the films were investi-gated by IMPS and IMVS The electron transit time (120591
119905) and
electron recombination time (120591119903) can be determined using
the equations 120591119905= 12120587119891min and 120591
119903= 12120587119891min1015840 In the
equations119891min and119891min1015840 are the frequencies giving the largestimaginary components in IMPS and IMVS respectively TheIMPS and IMVS plots are shown in Figure 5 Figure 6displays the diffusion coefficient of chitosan-based DSSCsand Table 3 shows the electron transport characteristic dataThe electron transit time of D1 D2 D3 and D4-based DSSCsis 3121 times 10minus3 2189 times 10minus3 2295 times 10minus3 and 4056 times10minus3 sminus1 respectively The electron recombination lifetimeof the D2-based DSSC was lower than those of the othersamples For the D2-based DSSC the recombination lifetimeis 6336 times 10minus2 s This result clearly indicates that electronrecombination with the oxidized species is reduced in theD2 TiO
2film This can be understood by either looking
at improvements in the network of TiO2nanoparticles or
at the electron behavior during transition in the D2-based
International Journal of Photoenergy 5
0 2 4 6 8 10 120
1
2
3
4
5
6
7
8
D1D2
D3D4
Z998400998400
(Wtimes
10minus4)
Z998400 (W times10minus4)minus2
(a)
D1D2
D3D4
0 1 2 3 4 500
05
10
15
20
25
30
Z998400998400
(Ωtimes
103)
Z998400 (Ω times103)
(b)Figure 5 Intensity modulation photocurrent spectroscopy (IMPS) and intensity modulation photovoltage spectroscopy (IMVS) of chitosansol-based DSSCs
Table 3 Charge transport parameter of the chitosan sol-basedDSSCs
TiO2film From the FE-SEM I-V and electron transport
characteristic results the D2-based DSSCs have a very goodfilm surface uniformity and high porosity Consequentlythe D2-based DSSCs have increased surface absorption andenhanced solar energy conversion efficiency
4 Conclusions
DSSCs were fabricated using different chitosan binder sol(15sim30 wt)-based photoelectrodesThe chitosan binder solhad low calcination temperature (sim150∘C) and successfullyprepared low temperature TiO
2photoelectrodes The D2
(sim20 wt)-based DSSCs had faster electron transit time andslower electron recombination time than the other samples(D1 D3 and D4) The D2-based DSSC exhibited highersolar conversion efficiencies than D1 D3 and D4-basedDSSCs because the electron recombination is more than 15sim3 times slower in the D2-based DSSC The electron diffusioncoefficient of the D2-based DSSC was 3463times 10minus5 cm2 sminus1
05 06 07 08 09 11
2
3
4
D1D2
D3D4
Voltage (V)
Diff
usio
n co
effici
ent (
cm2
sminus1times
10minus5)
Figure 6 Diffusion coefficient of chitosan sol-based DSSCs
and the diffusion length was 1481 120583m The efficiency ofthe D2 based DSSC was optimized to achieve 416 underillumination of simulated solar light AM 15 global (119881oc =069 V 119869sc = 1016mAcmminus2 fill factor is 5941)
Acknowledgment
This research was supported by Specialized Local IndustryDevelopment Program through Korea Institute for Advance-ment of Technology (KIAT) funded by theMinistry of Trade
6 International Journal of Photoenergy
Industry and Energy (1415127923-R0002040) And the BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation Science and Technology (2012010655)
References
[1] I J Kramer A G Pattantyus-Abraham A R Barkhouse et alldquoRETRACTED advances in colloidal quantum dot solar cellsthe depleted-heterojunction devicerdquo Thin Solid Films vol 519no 21 pp 7351ndash7355 2011
[2] D Kuang P Comte S M Zakeeruddin et al ldquoStable dye-sensitized solar cells based on organic chromophores and ionicliquid electrolyterdquo Solar Energy vol 85 no 6 pp 1189ndash11942011
[3] I KDing JMelas-Kyriazi N L Cevey-Ha et al ldquoDeposition ofhole-transport materials in solid-state dye-sensitized solar cellsby doctor-bladingrdquo Organic Electronics vol 11 no 7 pp 1217ndash1222 2010
[4] J H Yum S J Moon C S Karthikeyan et al ldquoHeterolep-tic ruthenium complex containing substituted triphenylaminehole-transport unit as sensitizer for stable dye-sensitized solarcellrdquo Nano Energy vol 1 no 1 pp 6ndash12 2012
[5] G Calogero J H Yum A Sinopoli G D Marco M Gratzeland M K Nazeeruddin ldquoAnthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cellsrdquo Solar Energyvol 86 no 5 pp 1563ndash1575 2012
[6] B OrsquoRegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO
2filmsrdquo Nature vol
353 no 6346 pp 737ndash740 1991[7] H Lindstrom A Holmberg E Magnusson L Malmqvist
and A Hagfeldt ldquoA new method to make dye-sensitizednanocrystalline solar cells at room temperaturerdquo Journal ofPhotochemistry and Photobiology A vol 145 no 1-2 pp 107ndash1122001
[8] B Tan and Y Wu ldquoDye-sensitized solar cells based on anataseTiO2nanoparticlenanowire compositesrdquo Journal of Physical
Chemistry B vol 110 no 32 pp 15932ndash15938 2006[9] E M Jin K H Park J J Yun et al ldquoPhotovoltaic properties
of TiO2photoelectrode prepared by using liquid PEG-EEM
binderrdquo Surface Review and Letters vol 17 no 1 pp 15ndash20 2010[10] K H Park H B Gu E M Jin and M Dhayal ldquoUsing hybrid
silica-conjugated TiO2nanostructures to enhance the efficiency
of dye-sensitized solar cellsrdquo Electrochimica Acta vol 55 no 19pp 5499ndash5505 2010
[11] S Hore C Vetter R Kern H Smit and A Hinsch ldquoInfluenceof scattering layers on efficiency of dye-sensitized solar cellsrdquoSolar Energy Materials and Solar Cells vol 90 no 9 pp 1176ndash1188 2006
[12] H Pettersson T Gruszecki L Johansson M O M EdwardsA Hagfeldt and T Matuszczyk ldquoDirect-driven electrochromicdisplays based on nanocrystalline electrodesrdquo Displays vol 25no 5 pp 223ndash230 2004
[13] E L Tae S H Lee J K Lee S S Yoo E J Kang andK B YoonldquoA strategy to increase the efficiency of the dye-sensitized TiO
2
solar cells operated by photoexcitation of dye-to-TiO2charge-
transfer bandsrdquo Journal of Physical Chemistry B vol 109 no 47pp 22513ndash22522 2005
[14] J Y Lin T J Chen and C K Hu ldquoEffects of anodic titaniumoxide nanotube arrays on dye-sensitized solar cellsrdquo Journal ofthe Chinese Chemical Society vol 57 no 5 pp 1176ndash1179 2010
[15] K Nelson and Y Deng ldquoEffect of polycrystalline structureof TiO
2particles on the light scattering efficiencyrdquo Journal of
Colloid and Interface Science vol 319 no 1 pp 130ndash139 2008[16] C S Chou R Y Yang C K Yeh and Y J Lin ldquoPreparation of
TiO2nano-metal composite particles and their applications in
dye-sensitized solar cellsrdquo Powder Technology vol 194 no 1-2pp 95ndash105 2009
[17] M C Kao H Z Chen S L Young C Y Kung and C C LinldquoThe effects of the thickness of TiO
2films on the performance
of dye-sensitized solar cellsrdquoThin Solid Films vol 517 no 17 pp5096ndash5099 2009
[18] F Odobel Y Pellegrin E A Gibson A Hagfeldt A L Smeighand L Hammarstrom ldquoRecent advances and future directionsto optimize the performances of p-type dye-sensitized solarcellsrdquo Coordination Chemistry Reviews vol 256 no 21-22 pp2414ndash2423 2012
[19] N Fuke A Fukui A Islam et al ldquoInfluence of TiO2electrode
interface on electron transport properties in back contact dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol93 no 6-7 pp 720ndash724 2009
[20] C Xu P H Shin L Cao J Wu and D Gao ldquoOrderedTiO2nanotube arrays on transparent conductive oxide for dye-
sensitized solar cellsrdquo Chemistry of Materials vol 22 no 1 pp143ndash148 2010
[21] Y B Tang C S Lee J Xu et al ldquoIncorporation of graphenesin nanostructured TiO
2films via molecular grafting for dye-
sensitized solar cell applicationrdquo ACS Nano vol 4 no 6 pp3482ndash3488 2010
[22] A S Nair R Jose Y Shengyuan and S Ramakrishna ldquoA simplerecipe for an efficient TiO
2nanofiber-based dye-sensitized solar
cellrdquo Journal of Colloid and Interface Science vol 353 no 1 pp39ndash45 2011
[23] A I Kontos A G Kontos D S Tsoukleris M Bernard NSpyrellis and P Falaras ldquoNanostructured TiO
2films for DSSCS
prepared by combining doctor-blade and sol-gel techniquesrdquoJournal of Materials Processing Technology vol 196 no 1ndash3 pp243ndash248 2008
[24] I Bernacka-Wojcik R Senadeera P J Wojcik et al ldquoInkjetprinted and ldquodoctor bladerdquo TiO
2photodetectors for DNA bio-
sensorsrdquo Biosensors and Bioelectronics vol 25 no 5 pp 1229ndash1234 2010
[25] N Nang Dinh N Minh Quyen D N Chung M Zikova andV V Truong ldquoHighly-efficient electrochromic performance ofnanostructured TiO 2 films made by doctor blade techniquerdquoSolar Energy Materials and Solar Cells vol 95 no 2 pp 618ndash623 2011
[26] Y Saito S Kambe T Kitamura Y Wada and S YanagidaldquoMorphology control of mesoporous TiO
2nanocrystalline
films for performance of dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol 83 no 1 pp 1ndash13 2004
[27] M Gratzel ldquoPhotovoltaic performance and long-term stabilityof dye-sensitized meosocopic solar cellsrdquo Comptes RendusChimie vol 9 no 5-6 pp 578ndash583 2006
[28] D Kuang C Klein H J Snaith R Humphry-Baker SM Zakeeruddin and M Gratzel ldquoA new ion-coordinatingruthenium sensitizer for mesoscopic dye-sensitized solar cellsrdquoInorganica Chimica Acta vol 361 no 3 pp 699ndash706 2008
[29] C C Yang H Q Zhang and Y R Zheng ldquoDSSC with a novelPt counter electrodes using pulsed electroplating techniquesrdquoCurrent Applied Physics vol 11 no 1 supplement pp S147ndashS1532011
International Journal of Photoenergy 7
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
(d)Figure 2 FE-SEM images of the surface morphologies of chitosan sol-based TiO
2films
in Figure 1 This shows that there is a large weight loss in therange from room temperature to 80∘C in the TG curve whichis due to the dehydration of the pure chitosan sol and chitosansol-based TiO
2paste This weight loss can be assigned to the
thermal decomposition of aqueous acetic acid in the purechitosan sol As shown in the TGA curve of D2 we can verifythat about 20wt residue is accurate and the residue canbe ascribed to the TiO
2powder So the heating temperature
of the TiO2photoelectrode (after TiO
2casting on the FTO
substrate) can be set to be very lowThe surface morphologies of the pure TiO
2photoelec-
trode and TiO2photoelectrode containing 15 wt (D1)
20 wt (D2) 25 wt (D3) and 30 wt (D4) of chitosanwere obtained by FE-SEM and are depicted in Figure 2 Ascan be seen in Figure 2 the TiO
2pastes containing different
weight of chitosan could result in the TiO2films having
different distributions of pore diameters It was found that theTiO2film prepared with the D2 paste shows a smaller pore
structure and that prepared with D1 D3 and D4 pastes has alarger pore diameter The penetration of electrolyte dependson the pore size and porosity of the TiO
2film [26] We will
investigate the influence on lifetime of the TiO2electrode as
well as the performance of the DSSC by varying the amountsof chitosan content in the TiO
2electrode
Figure 3 shows FE-SEM images of the cross-section ofchitosan sol-based TiO
2films In this figure the thickness of
TiO2ofD1 D2 D3 andD4 is 68 69 68 and 66 120583m respec-
tively The solar conversion efficiency of DSSCs dependsupon several factors including the porosity surface area andamount of dye loading [26]
Table 2 Photocurrent-voltage data of the chitosan sol-basedDSSCs
Figure 4 shows the photocurrent-voltage characteristicsof different chitosan-based DSSCs The solar cell was irra-diated with a 1000W xenon lamp with a light intensity of100mA cmminus2 as a light source As shown in Figure 4 theD2-based DSSC has a higher solar current density than theD1 D3 and D4-based DSSCs Table 2 shows the data of thephotocurrent-voltage characteristicsTheopen circuit voltage(119881oc) short-circuit current density (119869sc) fill factor (FF) andthe solar energy conversion efficiency (120578) of the D2-basedDSSC are 069V 1015mA cmminus2 5941 and 418 respec-tivelyThe 120578 of D1 D3 and D4-based DSSCs are 38 395327 respectively Gratzel and coworkers have reported ona highly efficient (7ndash11) photoelectrochemical cell basedon sensitized oxidation of iodide on a nanocrystalline TiO
2
electrode using an artificial binder [27 28] However we usednatural binder (chitosan) for TiO
2paste In comparison to the
artificial binder the efficiency of DSSCs using natural binderis not high However there is little data available on the useof natural binder for TiO
2paste in the literature Yang et al
4 International Journal of Photoenergy
68 120583m
D1
(a)
69 120583m
D2
(b)
68 120583m
D3
(c)
66 120583m
D4
(d)Figure 3 FE-SEM images of the cross-section of chitosan sol-based TiO
2films
Voltage (V)
00 01 02 03 04 05 06 070
2
4
6
8
10
12
D1D2
D3D4
Curr
ent d
ensit
y (m
Ac
m2)
Figure 4 Photocurrent-voltage curves of chitosan sol-basedDSSCs
[29] reported on a DSSC with a novel Pt counter electrodesusing pulsed electroplating techniques the efficiency ofDSSC was 385 Deepa et al [30] reported on efficiency
enhancement in DSSCs using metal nanoparticles a size-dependent study the efficiency of DSSCs range from 043 to152 Compared to the research of Yang et al and Deepa et althe efficiency of DSSCs using natural binder is highTheTiO
2
photoelectrode morphology can also influence photocurrentgeneration The higher efficiency of photocurrent generationhas been explained by a reduction in grain boundarieshigher dye loadings and slower recombination rates [31ndash35] The electron recombination lifetimes within DSSCs aredetermined primarily by the recombination of electrons withiodine electrolyte and oxidized sensitizers To understandthe charge transport characteristics the films were investi-gated by IMPS and IMVS The electron transit time (120591
119905) and
electron recombination time (120591119903) can be determined using
the equations 120591119905= 12120587119891min and 120591
119903= 12120587119891min1015840 In the
equations119891min and119891min1015840 are the frequencies giving the largestimaginary components in IMPS and IMVS respectively TheIMPS and IMVS plots are shown in Figure 5 Figure 6displays the diffusion coefficient of chitosan-based DSSCsand Table 3 shows the electron transport characteristic dataThe electron transit time of D1 D2 D3 and D4-based DSSCsis 3121 times 10minus3 2189 times 10minus3 2295 times 10minus3 and 4056 times10minus3 sminus1 respectively The electron recombination lifetimeof the D2-based DSSC was lower than those of the othersamples For the D2-based DSSC the recombination lifetimeis 6336 times 10minus2 s This result clearly indicates that electronrecombination with the oxidized species is reduced in theD2 TiO
2film This can be understood by either looking
at improvements in the network of TiO2nanoparticles or
at the electron behavior during transition in the D2-based
International Journal of Photoenergy 5
0 2 4 6 8 10 120
1
2
3
4
5
6
7
8
D1D2
D3D4
Z998400998400
(Wtimes
10minus4)
Z998400 (W times10minus4)minus2
(a)
D1D2
D3D4
0 1 2 3 4 500
05
10
15
20
25
30
Z998400998400
(Ωtimes
103)
Z998400 (Ω times103)
(b)Figure 5 Intensity modulation photocurrent spectroscopy (IMPS) and intensity modulation photovoltage spectroscopy (IMVS) of chitosansol-based DSSCs
Table 3 Charge transport parameter of the chitosan sol-basedDSSCs
TiO2film From the FE-SEM I-V and electron transport
characteristic results the D2-based DSSCs have a very goodfilm surface uniformity and high porosity Consequentlythe D2-based DSSCs have increased surface absorption andenhanced solar energy conversion efficiency
4 Conclusions
DSSCs were fabricated using different chitosan binder sol(15sim30 wt)-based photoelectrodesThe chitosan binder solhad low calcination temperature (sim150∘C) and successfullyprepared low temperature TiO
2photoelectrodes The D2
(sim20 wt)-based DSSCs had faster electron transit time andslower electron recombination time than the other samples(D1 D3 and D4) The D2-based DSSC exhibited highersolar conversion efficiencies than D1 D3 and D4-basedDSSCs because the electron recombination is more than 15sim3 times slower in the D2-based DSSC The electron diffusioncoefficient of the D2-based DSSC was 3463times 10minus5 cm2 sminus1
05 06 07 08 09 11
2
3
4
D1D2
D3D4
Voltage (V)
Diff
usio
n co
effici
ent (
cm2
sminus1times
10minus5)
Figure 6 Diffusion coefficient of chitosan sol-based DSSCs
and the diffusion length was 1481 120583m The efficiency ofthe D2 based DSSC was optimized to achieve 416 underillumination of simulated solar light AM 15 global (119881oc =069 V 119869sc = 1016mAcmminus2 fill factor is 5941)
Acknowledgment
This research was supported by Specialized Local IndustryDevelopment Program through Korea Institute for Advance-ment of Technology (KIAT) funded by theMinistry of Trade
6 International Journal of Photoenergy
Industry and Energy (1415127923-R0002040) And the BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation Science and Technology (2012010655)
References
[1] I J Kramer A G Pattantyus-Abraham A R Barkhouse et alldquoRETRACTED advances in colloidal quantum dot solar cellsthe depleted-heterojunction devicerdquo Thin Solid Films vol 519no 21 pp 7351ndash7355 2011
[2] D Kuang P Comte S M Zakeeruddin et al ldquoStable dye-sensitized solar cells based on organic chromophores and ionicliquid electrolyterdquo Solar Energy vol 85 no 6 pp 1189ndash11942011
[3] I KDing JMelas-Kyriazi N L Cevey-Ha et al ldquoDeposition ofhole-transport materials in solid-state dye-sensitized solar cellsby doctor-bladingrdquo Organic Electronics vol 11 no 7 pp 1217ndash1222 2010
[4] J H Yum S J Moon C S Karthikeyan et al ldquoHeterolep-tic ruthenium complex containing substituted triphenylaminehole-transport unit as sensitizer for stable dye-sensitized solarcellrdquo Nano Energy vol 1 no 1 pp 6ndash12 2012
[5] G Calogero J H Yum A Sinopoli G D Marco M Gratzeland M K Nazeeruddin ldquoAnthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cellsrdquo Solar Energyvol 86 no 5 pp 1563ndash1575 2012
[6] B OrsquoRegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO
2filmsrdquo Nature vol
353 no 6346 pp 737ndash740 1991[7] H Lindstrom A Holmberg E Magnusson L Malmqvist
and A Hagfeldt ldquoA new method to make dye-sensitizednanocrystalline solar cells at room temperaturerdquo Journal ofPhotochemistry and Photobiology A vol 145 no 1-2 pp 107ndash1122001
[8] B Tan and Y Wu ldquoDye-sensitized solar cells based on anataseTiO2nanoparticlenanowire compositesrdquo Journal of Physical
Chemistry B vol 110 no 32 pp 15932ndash15938 2006[9] E M Jin K H Park J J Yun et al ldquoPhotovoltaic properties
of TiO2photoelectrode prepared by using liquid PEG-EEM
binderrdquo Surface Review and Letters vol 17 no 1 pp 15ndash20 2010[10] K H Park H B Gu E M Jin and M Dhayal ldquoUsing hybrid
silica-conjugated TiO2nanostructures to enhance the efficiency
of dye-sensitized solar cellsrdquo Electrochimica Acta vol 55 no 19pp 5499ndash5505 2010
[11] S Hore C Vetter R Kern H Smit and A Hinsch ldquoInfluenceof scattering layers on efficiency of dye-sensitized solar cellsrdquoSolar Energy Materials and Solar Cells vol 90 no 9 pp 1176ndash1188 2006
[12] H Pettersson T Gruszecki L Johansson M O M EdwardsA Hagfeldt and T Matuszczyk ldquoDirect-driven electrochromicdisplays based on nanocrystalline electrodesrdquo Displays vol 25no 5 pp 223ndash230 2004
[13] E L Tae S H Lee J K Lee S S Yoo E J Kang andK B YoonldquoA strategy to increase the efficiency of the dye-sensitized TiO
2
solar cells operated by photoexcitation of dye-to-TiO2charge-
transfer bandsrdquo Journal of Physical Chemistry B vol 109 no 47pp 22513ndash22522 2005
[14] J Y Lin T J Chen and C K Hu ldquoEffects of anodic titaniumoxide nanotube arrays on dye-sensitized solar cellsrdquo Journal ofthe Chinese Chemical Society vol 57 no 5 pp 1176ndash1179 2010
[15] K Nelson and Y Deng ldquoEffect of polycrystalline structureof TiO
2particles on the light scattering efficiencyrdquo Journal of
Colloid and Interface Science vol 319 no 1 pp 130ndash139 2008[16] C S Chou R Y Yang C K Yeh and Y J Lin ldquoPreparation of
TiO2nano-metal composite particles and their applications in
dye-sensitized solar cellsrdquo Powder Technology vol 194 no 1-2pp 95ndash105 2009
[17] M C Kao H Z Chen S L Young C Y Kung and C C LinldquoThe effects of the thickness of TiO
2films on the performance
of dye-sensitized solar cellsrdquoThin Solid Films vol 517 no 17 pp5096ndash5099 2009
[18] F Odobel Y Pellegrin E A Gibson A Hagfeldt A L Smeighand L Hammarstrom ldquoRecent advances and future directionsto optimize the performances of p-type dye-sensitized solarcellsrdquo Coordination Chemistry Reviews vol 256 no 21-22 pp2414ndash2423 2012
[19] N Fuke A Fukui A Islam et al ldquoInfluence of TiO2electrode
interface on electron transport properties in back contact dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol93 no 6-7 pp 720ndash724 2009
[20] C Xu P H Shin L Cao J Wu and D Gao ldquoOrderedTiO2nanotube arrays on transparent conductive oxide for dye-
sensitized solar cellsrdquo Chemistry of Materials vol 22 no 1 pp143ndash148 2010
[21] Y B Tang C S Lee J Xu et al ldquoIncorporation of graphenesin nanostructured TiO
2films via molecular grafting for dye-
sensitized solar cell applicationrdquo ACS Nano vol 4 no 6 pp3482ndash3488 2010
[22] A S Nair R Jose Y Shengyuan and S Ramakrishna ldquoA simplerecipe for an efficient TiO
2nanofiber-based dye-sensitized solar
cellrdquo Journal of Colloid and Interface Science vol 353 no 1 pp39ndash45 2011
[23] A I Kontos A G Kontos D S Tsoukleris M Bernard NSpyrellis and P Falaras ldquoNanostructured TiO
2films for DSSCS
prepared by combining doctor-blade and sol-gel techniquesrdquoJournal of Materials Processing Technology vol 196 no 1ndash3 pp243ndash248 2008
[24] I Bernacka-Wojcik R Senadeera P J Wojcik et al ldquoInkjetprinted and ldquodoctor bladerdquo TiO
2photodetectors for DNA bio-
sensorsrdquo Biosensors and Bioelectronics vol 25 no 5 pp 1229ndash1234 2010
[25] N Nang Dinh N Minh Quyen D N Chung M Zikova andV V Truong ldquoHighly-efficient electrochromic performance ofnanostructured TiO 2 films made by doctor blade techniquerdquoSolar Energy Materials and Solar Cells vol 95 no 2 pp 618ndash623 2011
[26] Y Saito S Kambe T Kitamura Y Wada and S YanagidaldquoMorphology control of mesoporous TiO
2nanocrystalline
films for performance of dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol 83 no 1 pp 1ndash13 2004
[27] M Gratzel ldquoPhotovoltaic performance and long-term stabilityof dye-sensitized meosocopic solar cellsrdquo Comptes RendusChimie vol 9 no 5-6 pp 578ndash583 2006
[28] D Kuang C Klein H J Snaith R Humphry-Baker SM Zakeeruddin and M Gratzel ldquoA new ion-coordinatingruthenium sensitizer for mesoscopic dye-sensitized solar cellsrdquoInorganica Chimica Acta vol 361 no 3 pp 699ndash706 2008
[29] C C Yang H Q Zhang and Y R Zheng ldquoDSSC with a novelPt counter electrodes using pulsed electroplating techniquesrdquoCurrent Applied Physics vol 11 no 1 supplement pp S147ndashS1532011
International Journal of Photoenergy 7
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
(d)Figure 3 FE-SEM images of the cross-section of chitosan sol-based TiO
2films
Voltage (V)
00 01 02 03 04 05 06 070
2
4
6
8
10
12
D1D2
D3D4
Curr
ent d
ensit
y (m
Ac
m2)
Figure 4 Photocurrent-voltage curves of chitosan sol-basedDSSCs
[29] reported on a DSSC with a novel Pt counter electrodesusing pulsed electroplating techniques the efficiency ofDSSC was 385 Deepa et al [30] reported on efficiency
enhancement in DSSCs using metal nanoparticles a size-dependent study the efficiency of DSSCs range from 043 to152 Compared to the research of Yang et al and Deepa et althe efficiency of DSSCs using natural binder is highTheTiO
2
photoelectrode morphology can also influence photocurrentgeneration The higher efficiency of photocurrent generationhas been explained by a reduction in grain boundarieshigher dye loadings and slower recombination rates [31ndash35] The electron recombination lifetimes within DSSCs aredetermined primarily by the recombination of electrons withiodine electrolyte and oxidized sensitizers To understandthe charge transport characteristics the films were investi-gated by IMPS and IMVS The electron transit time (120591
119905) and
electron recombination time (120591119903) can be determined using
the equations 120591119905= 12120587119891min and 120591
119903= 12120587119891min1015840 In the
equations119891min and119891min1015840 are the frequencies giving the largestimaginary components in IMPS and IMVS respectively TheIMPS and IMVS plots are shown in Figure 5 Figure 6displays the diffusion coefficient of chitosan-based DSSCsand Table 3 shows the electron transport characteristic dataThe electron transit time of D1 D2 D3 and D4-based DSSCsis 3121 times 10minus3 2189 times 10minus3 2295 times 10minus3 and 4056 times10minus3 sminus1 respectively The electron recombination lifetimeof the D2-based DSSC was lower than those of the othersamples For the D2-based DSSC the recombination lifetimeis 6336 times 10minus2 s This result clearly indicates that electronrecombination with the oxidized species is reduced in theD2 TiO
2film This can be understood by either looking
at improvements in the network of TiO2nanoparticles or
at the electron behavior during transition in the D2-based
International Journal of Photoenergy 5
0 2 4 6 8 10 120
1
2
3
4
5
6
7
8
D1D2
D3D4
Z998400998400
(Wtimes
10minus4)
Z998400 (W times10minus4)minus2
(a)
D1D2
D3D4
0 1 2 3 4 500
05
10
15
20
25
30
Z998400998400
(Ωtimes
103)
Z998400 (Ω times103)
(b)Figure 5 Intensity modulation photocurrent spectroscopy (IMPS) and intensity modulation photovoltage spectroscopy (IMVS) of chitosansol-based DSSCs
Table 3 Charge transport parameter of the chitosan sol-basedDSSCs
TiO2film From the FE-SEM I-V and electron transport
characteristic results the D2-based DSSCs have a very goodfilm surface uniformity and high porosity Consequentlythe D2-based DSSCs have increased surface absorption andenhanced solar energy conversion efficiency
4 Conclusions
DSSCs were fabricated using different chitosan binder sol(15sim30 wt)-based photoelectrodesThe chitosan binder solhad low calcination temperature (sim150∘C) and successfullyprepared low temperature TiO
2photoelectrodes The D2
(sim20 wt)-based DSSCs had faster electron transit time andslower electron recombination time than the other samples(D1 D3 and D4) The D2-based DSSC exhibited highersolar conversion efficiencies than D1 D3 and D4-basedDSSCs because the electron recombination is more than 15sim3 times slower in the D2-based DSSC The electron diffusioncoefficient of the D2-based DSSC was 3463times 10minus5 cm2 sminus1
05 06 07 08 09 11
2
3
4
D1D2
D3D4
Voltage (V)
Diff
usio
n co
effici
ent (
cm2
sminus1times
10minus5)
Figure 6 Diffusion coefficient of chitosan sol-based DSSCs
and the diffusion length was 1481 120583m The efficiency ofthe D2 based DSSC was optimized to achieve 416 underillumination of simulated solar light AM 15 global (119881oc =069 V 119869sc = 1016mAcmminus2 fill factor is 5941)
Acknowledgment
This research was supported by Specialized Local IndustryDevelopment Program through Korea Institute for Advance-ment of Technology (KIAT) funded by theMinistry of Trade
6 International Journal of Photoenergy
Industry and Energy (1415127923-R0002040) And the BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation Science and Technology (2012010655)
References
[1] I J Kramer A G Pattantyus-Abraham A R Barkhouse et alldquoRETRACTED advances in colloidal quantum dot solar cellsthe depleted-heterojunction devicerdquo Thin Solid Films vol 519no 21 pp 7351ndash7355 2011
[2] D Kuang P Comte S M Zakeeruddin et al ldquoStable dye-sensitized solar cells based on organic chromophores and ionicliquid electrolyterdquo Solar Energy vol 85 no 6 pp 1189ndash11942011
[3] I KDing JMelas-Kyriazi N L Cevey-Ha et al ldquoDeposition ofhole-transport materials in solid-state dye-sensitized solar cellsby doctor-bladingrdquo Organic Electronics vol 11 no 7 pp 1217ndash1222 2010
[4] J H Yum S J Moon C S Karthikeyan et al ldquoHeterolep-tic ruthenium complex containing substituted triphenylaminehole-transport unit as sensitizer for stable dye-sensitized solarcellrdquo Nano Energy vol 1 no 1 pp 6ndash12 2012
[5] G Calogero J H Yum A Sinopoli G D Marco M Gratzeland M K Nazeeruddin ldquoAnthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cellsrdquo Solar Energyvol 86 no 5 pp 1563ndash1575 2012
[6] B OrsquoRegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO
2filmsrdquo Nature vol
353 no 6346 pp 737ndash740 1991[7] H Lindstrom A Holmberg E Magnusson L Malmqvist
and A Hagfeldt ldquoA new method to make dye-sensitizednanocrystalline solar cells at room temperaturerdquo Journal ofPhotochemistry and Photobiology A vol 145 no 1-2 pp 107ndash1122001
[8] B Tan and Y Wu ldquoDye-sensitized solar cells based on anataseTiO2nanoparticlenanowire compositesrdquo Journal of Physical
Chemistry B vol 110 no 32 pp 15932ndash15938 2006[9] E M Jin K H Park J J Yun et al ldquoPhotovoltaic properties
of TiO2photoelectrode prepared by using liquid PEG-EEM
binderrdquo Surface Review and Letters vol 17 no 1 pp 15ndash20 2010[10] K H Park H B Gu E M Jin and M Dhayal ldquoUsing hybrid
silica-conjugated TiO2nanostructures to enhance the efficiency
of dye-sensitized solar cellsrdquo Electrochimica Acta vol 55 no 19pp 5499ndash5505 2010
[11] S Hore C Vetter R Kern H Smit and A Hinsch ldquoInfluenceof scattering layers on efficiency of dye-sensitized solar cellsrdquoSolar Energy Materials and Solar Cells vol 90 no 9 pp 1176ndash1188 2006
[12] H Pettersson T Gruszecki L Johansson M O M EdwardsA Hagfeldt and T Matuszczyk ldquoDirect-driven electrochromicdisplays based on nanocrystalline electrodesrdquo Displays vol 25no 5 pp 223ndash230 2004
[13] E L Tae S H Lee J K Lee S S Yoo E J Kang andK B YoonldquoA strategy to increase the efficiency of the dye-sensitized TiO
2
solar cells operated by photoexcitation of dye-to-TiO2charge-
transfer bandsrdquo Journal of Physical Chemistry B vol 109 no 47pp 22513ndash22522 2005
[14] J Y Lin T J Chen and C K Hu ldquoEffects of anodic titaniumoxide nanotube arrays on dye-sensitized solar cellsrdquo Journal ofthe Chinese Chemical Society vol 57 no 5 pp 1176ndash1179 2010
[15] K Nelson and Y Deng ldquoEffect of polycrystalline structureof TiO
2particles on the light scattering efficiencyrdquo Journal of
Colloid and Interface Science vol 319 no 1 pp 130ndash139 2008[16] C S Chou R Y Yang C K Yeh and Y J Lin ldquoPreparation of
TiO2nano-metal composite particles and their applications in
dye-sensitized solar cellsrdquo Powder Technology vol 194 no 1-2pp 95ndash105 2009
[17] M C Kao H Z Chen S L Young C Y Kung and C C LinldquoThe effects of the thickness of TiO
2films on the performance
of dye-sensitized solar cellsrdquoThin Solid Films vol 517 no 17 pp5096ndash5099 2009
[18] F Odobel Y Pellegrin E A Gibson A Hagfeldt A L Smeighand L Hammarstrom ldquoRecent advances and future directionsto optimize the performances of p-type dye-sensitized solarcellsrdquo Coordination Chemistry Reviews vol 256 no 21-22 pp2414ndash2423 2012
[19] N Fuke A Fukui A Islam et al ldquoInfluence of TiO2electrode
interface on electron transport properties in back contact dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol93 no 6-7 pp 720ndash724 2009
[20] C Xu P H Shin L Cao J Wu and D Gao ldquoOrderedTiO2nanotube arrays on transparent conductive oxide for dye-
sensitized solar cellsrdquo Chemistry of Materials vol 22 no 1 pp143ndash148 2010
[21] Y B Tang C S Lee J Xu et al ldquoIncorporation of graphenesin nanostructured TiO
2films via molecular grafting for dye-
sensitized solar cell applicationrdquo ACS Nano vol 4 no 6 pp3482ndash3488 2010
[22] A S Nair R Jose Y Shengyuan and S Ramakrishna ldquoA simplerecipe for an efficient TiO
2nanofiber-based dye-sensitized solar
cellrdquo Journal of Colloid and Interface Science vol 353 no 1 pp39ndash45 2011
[23] A I Kontos A G Kontos D S Tsoukleris M Bernard NSpyrellis and P Falaras ldquoNanostructured TiO
2films for DSSCS
prepared by combining doctor-blade and sol-gel techniquesrdquoJournal of Materials Processing Technology vol 196 no 1ndash3 pp243ndash248 2008
[24] I Bernacka-Wojcik R Senadeera P J Wojcik et al ldquoInkjetprinted and ldquodoctor bladerdquo TiO
2photodetectors for DNA bio-
sensorsrdquo Biosensors and Bioelectronics vol 25 no 5 pp 1229ndash1234 2010
[25] N Nang Dinh N Minh Quyen D N Chung M Zikova andV V Truong ldquoHighly-efficient electrochromic performance ofnanostructured TiO 2 films made by doctor blade techniquerdquoSolar Energy Materials and Solar Cells vol 95 no 2 pp 618ndash623 2011
[26] Y Saito S Kambe T Kitamura Y Wada and S YanagidaldquoMorphology control of mesoporous TiO
2nanocrystalline
films for performance of dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol 83 no 1 pp 1ndash13 2004
[27] M Gratzel ldquoPhotovoltaic performance and long-term stabilityof dye-sensitized meosocopic solar cellsrdquo Comptes RendusChimie vol 9 no 5-6 pp 578ndash583 2006
[28] D Kuang C Klein H J Snaith R Humphry-Baker SM Zakeeruddin and M Gratzel ldquoA new ion-coordinatingruthenium sensitizer for mesoscopic dye-sensitized solar cellsrdquoInorganica Chimica Acta vol 361 no 3 pp 699ndash706 2008
[29] C C Yang H Q Zhang and Y R Zheng ldquoDSSC with a novelPt counter electrodes using pulsed electroplating techniquesrdquoCurrent Applied Physics vol 11 no 1 supplement pp S147ndashS1532011
International Journal of Photoenergy 7
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
TiO2film From the FE-SEM I-V and electron transport
characteristic results the D2-based DSSCs have a very goodfilm surface uniformity and high porosity Consequentlythe D2-based DSSCs have increased surface absorption andenhanced solar energy conversion efficiency
4 Conclusions
DSSCs were fabricated using different chitosan binder sol(15sim30 wt)-based photoelectrodesThe chitosan binder solhad low calcination temperature (sim150∘C) and successfullyprepared low temperature TiO
2photoelectrodes The D2
(sim20 wt)-based DSSCs had faster electron transit time andslower electron recombination time than the other samples(D1 D3 and D4) The D2-based DSSC exhibited highersolar conversion efficiencies than D1 D3 and D4-basedDSSCs because the electron recombination is more than 15sim3 times slower in the D2-based DSSC The electron diffusioncoefficient of the D2-based DSSC was 3463times 10minus5 cm2 sminus1
05 06 07 08 09 11
2
3
4
D1D2
D3D4
Voltage (V)
Diff
usio
n co
effici
ent (
cm2
sminus1times
10minus5)
Figure 6 Diffusion coefficient of chitosan sol-based DSSCs
and the diffusion length was 1481 120583m The efficiency ofthe D2 based DSSC was optimized to achieve 416 underillumination of simulated solar light AM 15 global (119881oc =069 V 119869sc = 1016mAcmminus2 fill factor is 5941)
Acknowledgment
This research was supported by Specialized Local IndustryDevelopment Program through Korea Institute for Advance-ment of Technology (KIAT) funded by theMinistry of Trade
6 International Journal of Photoenergy
Industry and Energy (1415127923-R0002040) And the BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation Science and Technology (2012010655)
References
[1] I J Kramer A G Pattantyus-Abraham A R Barkhouse et alldquoRETRACTED advances in colloidal quantum dot solar cellsthe depleted-heterojunction devicerdquo Thin Solid Films vol 519no 21 pp 7351ndash7355 2011
[2] D Kuang P Comte S M Zakeeruddin et al ldquoStable dye-sensitized solar cells based on organic chromophores and ionicliquid electrolyterdquo Solar Energy vol 85 no 6 pp 1189ndash11942011
[3] I KDing JMelas-Kyriazi N L Cevey-Ha et al ldquoDeposition ofhole-transport materials in solid-state dye-sensitized solar cellsby doctor-bladingrdquo Organic Electronics vol 11 no 7 pp 1217ndash1222 2010
[4] J H Yum S J Moon C S Karthikeyan et al ldquoHeterolep-tic ruthenium complex containing substituted triphenylaminehole-transport unit as sensitizer for stable dye-sensitized solarcellrdquo Nano Energy vol 1 no 1 pp 6ndash12 2012
[5] G Calogero J H Yum A Sinopoli G D Marco M Gratzeland M K Nazeeruddin ldquoAnthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cellsrdquo Solar Energyvol 86 no 5 pp 1563ndash1575 2012
[6] B OrsquoRegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO
2filmsrdquo Nature vol
353 no 6346 pp 737ndash740 1991[7] H Lindstrom A Holmberg E Magnusson L Malmqvist
and A Hagfeldt ldquoA new method to make dye-sensitizednanocrystalline solar cells at room temperaturerdquo Journal ofPhotochemistry and Photobiology A vol 145 no 1-2 pp 107ndash1122001
[8] B Tan and Y Wu ldquoDye-sensitized solar cells based on anataseTiO2nanoparticlenanowire compositesrdquo Journal of Physical
Chemistry B vol 110 no 32 pp 15932ndash15938 2006[9] E M Jin K H Park J J Yun et al ldquoPhotovoltaic properties
of TiO2photoelectrode prepared by using liquid PEG-EEM
binderrdquo Surface Review and Letters vol 17 no 1 pp 15ndash20 2010[10] K H Park H B Gu E M Jin and M Dhayal ldquoUsing hybrid
silica-conjugated TiO2nanostructures to enhance the efficiency
of dye-sensitized solar cellsrdquo Electrochimica Acta vol 55 no 19pp 5499ndash5505 2010
[11] S Hore C Vetter R Kern H Smit and A Hinsch ldquoInfluenceof scattering layers on efficiency of dye-sensitized solar cellsrdquoSolar Energy Materials and Solar Cells vol 90 no 9 pp 1176ndash1188 2006
[12] H Pettersson T Gruszecki L Johansson M O M EdwardsA Hagfeldt and T Matuszczyk ldquoDirect-driven electrochromicdisplays based on nanocrystalline electrodesrdquo Displays vol 25no 5 pp 223ndash230 2004
[13] E L Tae S H Lee J K Lee S S Yoo E J Kang andK B YoonldquoA strategy to increase the efficiency of the dye-sensitized TiO
2
solar cells operated by photoexcitation of dye-to-TiO2charge-
transfer bandsrdquo Journal of Physical Chemistry B vol 109 no 47pp 22513ndash22522 2005
[14] J Y Lin T J Chen and C K Hu ldquoEffects of anodic titaniumoxide nanotube arrays on dye-sensitized solar cellsrdquo Journal ofthe Chinese Chemical Society vol 57 no 5 pp 1176ndash1179 2010
[15] K Nelson and Y Deng ldquoEffect of polycrystalline structureof TiO
2particles on the light scattering efficiencyrdquo Journal of
Colloid and Interface Science vol 319 no 1 pp 130ndash139 2008[16] C S Chou R Y Yang C K Yeh and Y J Lin ldquoPreparation of
TiO2nano-metal composite particles and their applications in
dye-sensitized solar cellsrdquo Powder Technology vol 194 no 1-2pp 95ndash105 2009
[17] M C Kao H Z Chen S L Young C Y Kung and C C LinldquoThe effects of the thickness of TiO
2films on the performance
of dye-sensitized solar cellsrdquoThin Solid Films vol 517 no 17 pp5096ndash5099 2009
[18] F Odobel Y Pellegrin E A Gibson A Hagfeldt A L Smeighand L Hammarstrom ldquoRecent advances and future directionsto optimize the performances of p-type dye-sensitized solarcellsrdquo Coordination Chemistry Reviews vol 256 no 21-22 pp2414ndash2423 2012
[19] N Fuke A Fukui A Islam et al ldquoInfluence of TiO2electrode
interface on electron transport properties in back contact dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol93 no 6-7 pp 720ndash724 2009
[20] C Xu P H Shin L Cao J Wu and D Gao ldquoOrderedTiO2nanotube arrays on transparent conductive oxide for dye-
sensitized solar cellsrdquo Chemistry of Materials vol 22 no 1 pp143ndash148 2010
[21] Y B Tang C S Lee J Xu et al ldquoIncorporation of graphenesin nanostructured TiO
2films via molecular grafting for dye-
sensitized solar cell applicationrdquo ACS Nano vol 4 no 6 pp3482ndash3488 2010
[22] A S Nair R Jose Y Shengyuan and S Ramakrishna ldquoA simplerecipe for an efficient TiO
2nanofiber-based dye-sensitized solar
cellrdquo Journal of Colloid and Interface Science vol 353 no 1 pp39ndash45 2011
[23] A I Kontos A G Kontos D S Tsoukleris M Bernard NSpyrellis and P Falaras ldquoNanostructured TiO
2films for DSSCS
prepared by combining doctor-blade and sol-gel techniquesrdquoJournal of Materials Processing Technology vol 196 no 1ndash3 pp243ndash248 2008
[24] I Bernacka-Wojcik R Senadeera P J Wojcik et al ldquoInkjetprinted and ldquodoctor bladerdquo TiO
2photodetectors for DNA bio-
sensorsrdquo Biosensors and Bioelectronics vol 25 no 5 pp 1229ndash1234 2010
[25] N Nang Dinh N Minh Quyen D N Chung M Zikova andV V Truong ldquoHighly-efficient electrochromic performance ofnanostructured TiO 2 films made by doctor blade techniquerdquoSolar Energy Materials and Solar Cells vol 95 no 2 pp 618ndash623 2011
[26] Y Saito S Kambe T Kitamura Y Wada and S YanagidaldquoMorphology control of mesoporous TiO
2nanocrystalline
films for performance of dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol 83 no 1 pp 1ndash13 2004
[27] M Gratzel ldquoPhotovoltaic performance and long-term stabilityof dye-sensitized meosocopic solar cellsrdquo Comptes RendusChimie vol 9 no 5-6 pp 578ndash583 2006
[28] D Kuang C Klein H J Snaith R Humphry-Baker SM Zakeeruddin and M Gratzel ldquoA new ion-coordinatingruthenium sensitizer for mesoscopic dye-sensitized solar cellsrdquoInorganica Chimica Acta vol 361 no 3 pp 699ndash706 2008
[29] C C Yang H Q Zhang and Y R Zheng ldquoDSSC with a novelPt counter electrodes using pulsed electroplating techniquesrdquoCurrent Applied Physics vol 11 no 1 supplement pp S147ndashS1532011
International Journal of Photoenergy 7
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
Industry and Energy (1415127923-R0002040) And the BasicScience Research Program through the National ResearchFoundation of Korea (NRF) funded by the Ministry ofEducation Science and Technology (2012010655)
References
[1] I J Kramer A G Pattantyus-Abraham A R Barkhouse et alldquoRETRACTED advances in colloidal quantum dot solar cellsthe depleted-heterojunction devicerdquo Thin Solid Films vol 519no 21 pp 7351ndash7355 2011
[2] D Kuang P Comte S M Zakeeruddin et al ldquoStable dye-sensitized solar cells based on organic chromophores and ionicliquid electrolyterdquo Solar Energy vol 85 no 6 pp 1189ndash11942011
[3] I KDing JMelas-Kyriazi N L Cevey-Ha et al ldquoDeposition ofhole-transport materials in solid-state dye-sensitized solar cellsby doctor-bladingrdquo Organic Electronics vol 11 no 7 pp 1217ndash1222 2010
[4] J H Yum S J Moon C S Karthikeyan et al ldquoHeterolep-tic ruthenium complex containing substituted triphenylaminehole-transport unit as sensitizer for stable dye-sensitized solarcellrdquo Nano Energy vol 1 no 1 pp 6ndash12 2012
[5] G Calogero J H Yum A Sinopoli G D Marco M Gratzeland M K Nazeeruddin ldquoAnthocyanins and betalains as light-harvesting pigments for dye-sensitized solar cellsrdquo Solar Energyvol 86 no 5 pp 1563ndash1575 2012
[6] B OrsquoRegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO
2filmsrdquo Nature vol
353 no 6346 pp 737ndash740 1991[7] H Lindstrom A Holmberg E Magnusson L Malmqvist
and A Hagfeldt ldquoA new method to make dye-sensitizednanocrystalline solar cells at room temperaturerdquo Journal ofPhotochemistry and Photobiology A vol 145 no 1-2 pp 107ndash1122001
[8] B Tan and Y Wu ldquoDye-sensitized solar cells based on anataseTiO2nanoparticlenanowire compositesrdquo Journal of Physical
Chemistry B vol 110 no 32 pp 15932ndash15938 2006[9] E M Jin K H Park J J Yun et al ldquoPhotovoltaic properties
of TiO2photoelectrode prepared by using liquid PEG-EEM
binderrdquo Surface Review and Letters vol 17 no 1 pp 15ndash20 2010[10] K H Park H B Gu E M Jin and M Dhayal ldquoUsing hybrid
silica-conjugated TiO2nanostructures to enhance the efficiency
of dye-sensitized solar cellsrdquo Electrochimica Acta vol 55 no 19pp 5499ndash5505 2010
[11] S Hore C Vetter R Kern H Smit and A Hinsch ldquoInfluenceof scattering layers on efficiency of dye-sensitized solar cellsrdquoSolar Energy Materials and Solar Cells vol 90 no 9 pp 1176ndash1188 2006
[12] H Pettersson T Gruszecki L Johansson M O M EdwardsA Hagfeldt and T Matuszczyk ldquoDirect-driven electrochromicdisplays based on nanocrystalline electrodesrdquo Displays vol 25no 5 pp 223ndash230 2004
[13] E L Tae S H Lee J K Lee S S Yoo E J Kang andK B YoonldquoA strategy to increase the efficiency of the dye-sensitized TiO
2
solar cells operated by photoexcitation of dye-to-TiO2charge-
transfer bandsrdquo Journal of Physical Chemistry B vol 109 no 47pp 22513ndash22522 2005
[14] J Y Lin T J Chen and C K Hu ldquoEffects of anodic titaniumoxide nanotube arrays on dye-sensitized solar cellsrdquo Journal ofthe Chinese Chemical Society vol 57 no 5 pp 1176ndash1179 2010
[15] K Nelson and Y Deng ldquoEffect of polycrystalline structureof TiO
2particles on the light scattering efficiencyrdquo Journal of
Colloid and Interface Science vol 319 no 1 pp 130ndash139 2008[16] C S Chou R Y Yang C K Yeh and Y J Lin ldquoPreparation of
TiO2nano-metal composite particles and their applications in
dye-sensitized solar cellsrdquo Powder Technology vol 194 no 1-2pp 95ndash105 2009
[17] M C Kao H Z Chen S L Young C Y Kung and C C LinldquoThe effects of the thickness of TiO
2films on the performance
of dye-sensitized solar cellsrdquoThin Solid Films vol 517 no 17 pp5096ndash5099 2009
[18] F Odobel Y Pellegrin E A Gibson A Hagfeldt A L Smeighand L Hammarstrom ldquoRecent advances and future directionsto optimize the performances of p-type dye-sensitized solarcellsrdquo Coordination Chemistry Reviews vol 256 no 21-22 pp2414ndash2423 2012
[19] N Fuke A Fukui A Islam et al ldquoInfluence of TiO2electrode
interface on electron transport properties in back contact dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol93 no 6-7 pp 720ndash724 2009
[20] C Xu P H Shin L Cao J Wu and D Gao ldquoOrderedTiO2nanotube arrays on transparent conductive oxide for dye-
sensitized solar cellsrdquo Chemistry of Materials vol 22 no 1 pp143ndash148 2010
[21] Y B Tang C S Lee J Xu et al ldquoIncorporation of graphenesin nanostructured TiO
2films via molecular grafting for dye-
sensitized solar cell applicationrdquo ACS Nano vol 4 no 6 pp3482ndash3488 2010
[22] A S Nair R Jose Y Shengyuan and S Ramakrishna ldquoA simplerecipe for an efficient TiO
2nanofiber-based dye-sensitized solar
cellrdquo Journal of Colloid and Interface Science vol 353 no 1 pp39ndash45 2011
[23] A I Kontos A G Kontos D S Tsoukleris M Bernard NSpyrellis and P Falaras ldquoNanostructured TiO
2films for DSSCS
prepared by combining doctor-blade and sol-gel techniquesrdquoJournal of Materials Processing Technology vol 196 no 1ndash3 pp243ndash248 2008
[24] I Bernacka-Wojcik R Senadeera P J Wojcik et al ldquoInkjetprinted and ldquodoctor bladerdquo TiO
2photodetectors for DNA bio-
sensorsrdquo Biosensors and Bioelectronics vol 25 no 5 pp 1229ndash1234 2010
[25] N Nang Dinh N Minh Quyen D N Chung M Zikova andV V Truong ldquoHighly-efficient electrochromic performance ofnanostructured TiO 2 films made by doctor blade techniquerdquoSolar Energy Materials and Solar Cells vol 95 no 2 pp 618ndash623 2011
[26] Y Saito S Kambe T Kitamura Y Wada and S YanagidaldquoMorphology control of mesoporous TiO
2nanocrystalline
films for performance of dye-sensitized solar cellsrdquo Solar EnergyMaterials and Solar Cells vol 83 no 1 pp 1ndash13 2004
[27] M Gratzel ldquoPhotovoltaic performance and long-term stabilityof dye-sensitized meosocopic solar cellsrdquo Comptes RendusChimie vol 9 no 5-6 pp 578ndash583 2006
[28] D Kuang C Klein H J Snaith R Humphry-Baker SM Zakeeruddin and M Gratzel ldquoA new ion-coordinatingruthenium sensitizer for mesoscopic dye-sensitized solar cellsrdquoInorganica Chimica Acta vol 361 no 3 pp 699ndash706 2008
[29] C C Yang H Q Zhang and Y R Zheng ldquoDSSC with a novelPt counter electrodes using pulsed electroplating techniquesrdquoCurrent Applied Physics vol 11 no 1 supplement pp S147ndashS1532011
International Journal of Photoenergy 7
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
[30] K G Deepa P Lekha and S Sindhu ldquoEfficiency enhancementin DSSC using metal nanoparticles a size dependent studyrdquoSolar Energy vol 86 no 1 pp 326ndash330 2012
[31] K Fujihara A Kumar R Jose S Ramakrishna and S UchidaldquoSpray deposition of electrospun TiO
2nanorods for dye-
sensitized solar cellrdquo Nanotechnology vol 18 no 36 Article ID365709 2007
[32] J B Baxter and E S Aydil ldquoDye-sensitized solar cells basedon semiconductor morphologies with ZnO nanowiresrdquo SolarEnergy Materials and Solar Cells vol 90 no 5 pp 607ndash6222006
[33] M Adachi Y Murata J Takao J Jiu M Sakamoto and FWang ldquoHighly efficient dye-sensitized solar cells with a titaniathin-film electrode composed of a network structure of single-crystal-like TiO
2nanowires made by the ldquooriented attachmentrdquo
mechanismrdquo Journal of the American Chemical Society vol 126no 45 pp 14943ndash14949 2004
[34] S H Kang S H Choi M S Kang et al ldquoNanorod-baseddye-sensitized solar cells with improved charge collection effi-ciencyrdquo Advanced Materials vol 20 no 1 pp 54ndash58 2008
[35] K Zhu N R Neale A Miedaner and A J Frank ldquoEnhancedcharge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO
![Index [application.wiley-vch.de] · 2020-01-17 · 266 Index drug delivery micelles 108 dye‐sensitized solar cells (DSSCs) 169 e electrochromic device m182, 185, 187 electrochromic](https://static.documents.pub/doc/80x56/5f08b3147e708231d4234b4b/index-2020-01-17-266-index-drug-delivery-micelles-108-dyeasensitized-solar.jpg)
