Plasmon Enhanced Solar Cells
Björn Törngren,1 Simon Sandén,2 Kenta Akitsu,3 Takaya Kubo,3
Hiroshi Segawa,3 Ronald Österbacka,2 Jan-Henrik Smått1
1 Center for Functional Materials, Physical Chemistry, Åbo Akademi University, Turku, Finland.
2 Center for Functional Materials, Physics, Åbo Akademi University, Turku, Finland.
3 Research Center for Advanced Science and Technology (RCAST),
The University of Tokyo, Tokyo, Japan
FunMat annual symposium – Helsinki 14.08.2013
Joint project with RCAST
Plasmon Enhanced Organic Hybrid Solar Cells (POHSC) – 3 yr
Physical Chemistry (Lindén/Smått) and Physics (Österbacka)
Research Center for Advanced Science and Technology (RCAST), The
University of Tokyo, Japan (Prof. Segawa)
Several research visits between Finland and Japan
POHSC – general outline
PhysChem (ÅAU):
Synthesis and
modification of core-
shell nanoparticles
RCAST (UT):
Development of novel
dyes (NIR) –
porphyrin-based
Solar cell applications:
Assembly into DSSC and organic SC
Physics (ÅAU):
Modeling of
plasmonic core-shell
particles
Plasmon enhanced NPs
NPs with
tunable
absorption
properties 300 400 500 600 700 800 900
Ab
sorb
an
ce
(a.u
.)
Wavelength (nm)
Surface plasmons (SPs) are coherent oscillations of conduction
electrons on a metal surface excited by electromagnetic radiation
at a metal-dielectric interface
Resonance at a specific wavelength (Au NPs: ~530 nm)
Willets, K. A.; Van Duyne, R. P. Ann. Rev. Phys. Chem. 2006, 58, 267.
The surface plasmon effect
10 nm
Glass
ITO
P3HT
PCBM
Gold
P3HT PCBM
Dye-sensitized solar cells Organic or hybrid solar cells
Surface plasmons in solar cells
Current topics of the project
Stability issues of core/shell nanoparticles in DSSCs
Plasmon-enhanced polymer-sensitized solar cells
(PSSC)
Charge generation and charge transport studies
Gold nanorods to modify the light absorption range
Plasmonic particles in organic bulk hetero-junction
solar cells
Core-shell Au@SiO2 nanoparticles
Why is a thin silica shell needed?
Prevents quenching of the generated
plasmons
Should be thin enough to allow the
dye molecules to be close enough
(near-field enhancement)
Gold is very soluble in the electrolyte
solution used in DSSCs (I3–)
A silica coating protects the gold core
Sheehan et al. J. Phys. Chem. C, 2013, 117, 927−934
Synthesis approaches
Turkevich approach:
~15 nm gold cores
Na2SiO3
Coating thickness and completeness APS APS +
Stöber
MPTMS Direct Stöber
Gold core diameter: 16 nm
Modeling of silica thickness (Mie theory)
APS: 0.5 nm APS + Stöber: 5 nm MPTMS: 1.3 nm Direct Stöber: ~20 nm
Chemical stability in iodide electrolyte
Coating methods:
A: APS B: APS + Stöber
C: Direct Stöber D: MPTMS
Temperature stability of Au@SiO2 NPs
Au@SiO2 NPs (MPTMS method)
RT 500 ºC
Heating required for sintering of TiO2 NPs in a DSSC could
potentially damage the silica shell No detectable difference!
Assembly of (plasmon-enhanced) DSSC
TiO2 nanoparticle paste (w/ or w/o Au@SiO2 NPs) screen-printed on the substrate, and sintered at 500 °C
Electrolyte injection Placing two electrodes
FTO/Glass substrate
TiO2 nanoporous layer
Pt coated-FTO
The TiO2 substrate was immersed in the solution overnight
Solar cell structure
Dye solution
Photoanode
Spacer
Injection hole
Electrolyte
(30 µm)
Pt-coated FTO
Photoanode
Solar cell fabrication (I3
–/I– redox couple
in acetonitrile)
Slide courtesy of Kenta Akitsu
Plasmon-enhanced DSSC performance
Sample Au@SiO2 Thickness
[µm]
VOC
[V]
JSC
[mA/cm2]
FF PCE
[%]
A1 1 wt% 1.726 0.85 4.0 0.68 2.3
A2 1 wt% 1.899 0.85 3.9 0.68 2.3
T1 – 1.844 0.85 3.7 0.68 2.2
T2 – 1.868 0.85 3.4 0.69 2.0
B. Törngren et al. J. Colloid Interface Sci., in preparation.
Polymer-sensitized solar cell (PSSC)
Polythiophene derivative polymers where
COOH units are attached to the polymer
backbone to facilitate sensitization to TiO2
Uses a low molecular weight polymer as
dye (here: PT-C 85, i.e. HR 85%)
Electrolyte solution
Pt/FTO
TiO2/Polymer FTO
R=H, Me
PT derivative with carboxylic acid groups
MW: 1100, 2700
Hydrolysis ratio (H:Me ratio)
can be varied 0%-95%
Akitsu et al. Jpn. J. Appl. Phys. 51 (2012) 10NE04
Plasmon-enhanced PSSCs
TiO2 paste incorporating 1 wt% Au@SiO2 NPs was manufactured
Photoanode was made by screen-printing on FTO
PT-C 85 was adsorbed onto the TiO2 layer overnight
Akitsu et al., in preparation.
I-V and IPCE of Plasmon Enhanced PSSCs 7
6
5
4
3
2
1
0
Cu
rren
t d
ensi
y,
mA
/cm
2
0.60.50.40.30.20.10
Voltage, V
70
60
50
40
30
20
10
0
IPC
E,
%
700600500400300
Voltage, V
3 layers
2 layers
1 layer
Sample Voc Jsc FF
Au 1 0.52 2.2 0.55 0.6
Ref 1 0.52 1.1 0.52 0.3
Au 2 0.53 4.6 0.55 1.3
Ref 2 0.50 3.7 0.55 1.0
Au 3 0.53 5.9 0.51 1.6
Ref 3 0.50 5.0 0.54 1.4
Dashed: with
Au@SiO2 NPs
Solid: without
Au@SiO2 NPs
IPCE enhancement factor: IPCE(Au)/IPCE(Ref)
IPCE enhancement over 400-650 nm
Peak slightly red-shifted compared to absorption of Au@SiO2 NPs
in EtOH larger dielectric constant of TiO2
3.0
2.5
2.0
1.5
1.0
0.5
Au/R
ef., -
650600550500450400350300
Wavelength, nm
1.4
1.2
1.0
0.8
0.6
Au/R
ef., -
650600550500450400350300
Wavelength, nm
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Abso
rban
ce, -
Au@SiO2 NPs in EtOH
Outlook of other possibilities
Au nanorods to enhance
absorption in NIR region
Plasmonic particles in organic
BHJ solar cells
0
0.2
0.4
0.6
0.8
1
1.2
1.4
300 400 500 600 700 800 900
Ab
sorb
an
ce (
a.u
.)
Wavelength (nm)
Gold nanoparticles
Gold nanorods
Longitudinal
mode
Aspect ratio ~3
Transverse
mode
10 nm
Glass
ITO
P3HT PCBM Gold
Au NPs
Summary
Plasmonic particles (e.g. gold nanoparticles) have proven
useful for improving the efficiency of photovoltaic devices
A thin but complete silica shell is needed to protect the Au
NPs in the harsh electrolyte solutions used in DSSCs
Plasmon-enhanced polymer-senisitized solar cells (PSSCs)
have been manufactured using novel polythiophene
derivative polymers
In both DSSCs and PSSCs the efficiency can be improved by
incorporating Au@SiO2 nanoparticles
Make your own DSSC
Within FunMat we would
like to give you the
opportunity to learn how
to make your own DSSCs
The plan is to start
sometime during the fall
Contact Björn Törngren
([email protected]) for
more information
Screen-printer device at ÅAU