Techniques to Study Degradation in PVs
K.S. Narayan
Jawaharlal Nehru Centre for Advanced Scientific Research
Bangalore India
Inorganic Semiconductors Band transport High mobility large carrier diffusion length
organic Semiconductors Tunable Band-gap Solution Processable Low temperature, low cost
manufacturing
Organic inorganic halide Perovskite
Organo Metal Halide Perovskite
The rapid evolution of highly efficient perovskite solar cells Correa-Baena et al EES 2017
Degradation in Perovskite Solar Cells
Major kinds of degradation in perovskite solar cells
➢Oxygen induced degradation
➢Light induced degradation
➢Moisture induced degradation
➢Temperature induced degradation
➢Thermal and electric field induced intrinsic degradation
Taame Abraha Berhe, Bing-Joe Hwang, Organometal halide perovskite solar cells:degradation and stability, Energy Environ. Sci.,2016, 9, 323 4
“Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment,” RoHS1 in 2003 and the subsequent RoHS2 in 2011, which are also known as the “lead-free directives.”The RoHS takes into account the more recent understanding of long-term risks associated with continuous exposure to low levels of toxic heavy metals. Specifically, it restricts to 0.1% in weight the maximum concentration of lead in each homogeneous material contained in any electronic devices, i.e., the perovskite within a PSC. Unfortunately, all the halide perovskites that have been so far demonstrated as effective photovoltaic materials contain more than 10% lead in weight.
Lead Content of Sindoor, a Hindu Religious Powder and Cosmetic: New Jersey and India, 2014–2015
•American Journal of Public Health (ajph) October
2017
Results. Analysis determined that 79 (83.2%) sindoor samples purchased in the United States and 18 (78.3%) samples purchased in India contained 1.0 or more micrograms of lead per gram of powder. For US samples, geometric mean concentration was 5.4 micrograms per gram compared with 28.1 micrograms per gram for India samples. ..Of the examined US sindoorsamples, 19% contained more than 20 micrograms per gram of lead (US Food and Drug Administration [FDA] limit); 43% of the India samples exceeded this limit.
Conclusions. Results suggested continued need for lead monitoring in sindoorin the United States and in sindoor carried into the United States by travelersfrom India, despite FDA warnings.
T= 293 K a = b = 8.849 Å , c = 12.642 ÅAd = 104.2 mg/m2
T =400 Ka = b = 6.3115 Å , c = 6.3161 ÅAd = 410 mg/m2
Note : In general T > 330 K Cubic phase160K < T <330 K Tetragonal PhaseT <160 K Orthorhombic Phase
References : 1) Fabini, Douglas. "Quantifying the potential for lead pollution from halide perovskite photovoltaics." (2015): 3546-3548.
2) Stoumpos, Constantinos C., Christos D. Malliakas, and Mercouri G. Kanatzidis. "Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties." Inorganic chemistry 52.15 (2013): 9019-9038.
Health hazards of methylammonium lead iodide based perovskites: cytotoxicity studiesIness R. Benmessaoud,a Anne-Laure Mahul-Mellier,b Endre Horváth,a Bohumil Maco,b Massimo Spina,a Hilal A. Lashuel*b and Làszló Forró*a Author affiliationsAbstract
New technologies launch novel materials; besides their performances in products, their health hazards must be tested. This applies to the lead halide perovskite CH3NH3PbI3 as well, which offers fulgurate applications in photovoltaic devices. We report the effects of CH3NH3PbI3 photovoltaic perovskites in human lung adenocarcinoma epithelial cells (A549), human dopaminergicneuroblastoma cells (SH-SY5Y) and murine primary hippocampal neurons by using multiple assays and electron microscopy studies. In cell culture media the major part of the dissolved CH3NH3PbI3 has a strong cell-type dependent effect. Hippocampal primary neurons and neuroblastoma cells suffer a massive apoptotic cell death, whereas exposure to lung epithelial cells dramatically alters the kinetics of proliferation, metabolic activity and cellular morphology without inducing noticeable cell death. Our findings underscore the critical importance of conducting further studies to investigate the effect of short and long-term exposure to CH3NH3PbI3 on health and environment.
➢ Imperative and quantitative signatures of degradation preferably in-situ conditions will be useful.
➢ Reliable tool to diagnose at a relatively early stages
➢ Lack of clear understanding of the multitude of defect evolvement processes and their role in carrier transport mechanisms in perovskite-based devices.
9
IEA: “Review of Failures of Photovoltaic Modules” 2014
Transport ModelsDrift - Diffusion
∂n∂t = ∇・ (μnn∇φ + Dn∇n)+G−R
∂ p∂t = ∇・ (Dp∇p−μpp∇φ)+G−R
∇・ (ε∇φ) = −q(p−n+Nd)
the carrier concentrations in terms of quasi-Fermi levels
J = drift + diffusion
AmbipolarCoupled
Traps and Defects
Recombination Shockley-Read-HallMany sources for recombination in solar cells. In General,recombination at low excitation levels arises primarily from defect or trap states.
Monomolecular recombination: 1st order kinetics -minority carrier concentration when one carrier type predominates. R – Rate of recombination
where nt (pt) is the density of electrons (holes) in filled traps and τn (τp) is the time for electrons (holes) to be captured by trap states.
We can explicitly write nt as the product of the density of traps and a capturecross-section, tn = ntBn
Neeman 3rd edn
Surface and grain boundary recombinationSurfaces and grain boundaries represent regions where there are likely to be a large concentration of trap states, due to broken bonds and higher concentrations of impurities.Because the traps are concentrated in a small space, it is more useful to consider the density per unit area than per unit length.
We can define the surface recombination velocities, Sn,p by multiplying the density of traps per unit area, Nt with the capture cross-section, Bn . The recombination times, τn,p are equal to the product of the thickness of the layer (Δx) and Sn,p
Band-to-band recombination involves the recombination of an electron and hole withoutan intermediate stage, and therefore is bimolecular in the low-doping case. Balancingwith band-to-band generation in equilibrium, we have the net rate of recombination asRbb = B(np−n2
i) for B the bimolecular recombination constant. In direct-bandgapsemiconductors, this process is optically generated, otherwise it may also involve phononabsorption or emission.
14
dAtAJtI
At
tAQtAJ
,
1,,
nqQ
constantt
n
constant0
t
n
Source of noise in kinetic processes, time-
dependent terms?
Reasonable to expect noise in ISC of BHJs ?
Sources of noise in Solar Cells
14-Dec-17 15
ij
ij
B
ij
ij
ij
εTk
a
ra
for 1
for exp
2exp0
Origin of fluctuation : Microscopic model
Ltr or tr
No
. of
cou
nts
Etr = 0
E
Shallow traps
Deeptraps
ij
X= 0 X= LEtr = 0
E
Shallow traps
Deeptraps
ij
X= 0 X= L
Photocurrent Iph(t) : CW illuminationFluctuation d Iph(t) = Iph(t) – Iph(t)Noise powerTypically 100 samples,100ms sequences with4ms interval measurements
17
Noise Models
➢ Primary reason for noise , conductivity fluctuations
➢ For constant mobility,
Change in conductiviyy related to fluctuation in number density of charge carriers,
McWhorter Model
➢ For a fixed number density,
Change in conductiviy related to fluctuation in mobility of charge carriers,
Hooge Model
m en
ne m
m en 𝑺𝑰 𝒇 = 𝑨𝒏𝑰𝛃
𝒇𝜶
18
Current fluctuation in solar cell
light
dark
G/eV1P*
P
huP+…A-
Separatedcharges
Boundpolaron pair
P+ + A-Transport
to electrodes
Bimolecularrecombination (ns – ms)
Geminate Recombination (ps – ns)
19
Noise measurement as a function of
✓ Temperature✓ Intensity✓ Device efficiency
M. Bag, N. S. Vidhyadhiraja and K. S. Narayan (Appl. Phys. Lett. 2012)
Anode
Bulk-heterostructure solar cells
20
Temperature Dependence of Fluctuations
21
➢ Current or conductivity fluctuations, Δσ =Δ(qnµ) are related to the fluctuations in charge carrier density (ΔN model) or mobility fluctuations (Δµ model)
𝑺𝑰 𝒇 = 𝑨𝒏𝑰𝛃
𝒇𝜶
➢ The current noise spectra are usually analyzed by Hooge’s empirical
relation and is expressed as:
Here ‘An’ is the noise magnitude coefficient.
➢ Further analyses can be made in terms of relative or normalized power
spectrum density (NPSD) by normalizing the power spectrum density by Iβ.
𝑺 𝒇 ∝𝑺𝑰 𝒇
𝑰𝜷∝
𝟏
𝑵 𝒇𝜶
➢ The generation-recombination noise originates from the number
fluctuation. Its PSD can be expressed in the Lorentzian form:
𝑺𝑰(𝒇) =𝑺𝟎
[𝟏 + 𝟐𝝅𝒇𝝉𝟐]
where S0 is the part of SI(f) which is independent of the frequency, as seen at
f < 1/ 2πτ. τ is the time constant related to a particular trapping state. 22
Materials and Methods
➢ FTO/TiO2/Perovskite/Spiro-MeOTAD
➢ FTO/C60 / Perovskite/ Spiro-MeOTAD
➢ FTO/polyTPD/Perovskite/PCBM/BCP
Fabricated in Clarendon Laboratory, Dept. of Physics University of Oxford (U.K.) 23
24
J-V characteristic
1/f noise as in the PSD under outdoor conditions
25
Poly(4-butylphenyl-diphenyl-amine)
N2,N2,N2′,N2′,N7,N7,N7′,N7′-octakis(4-methoxyphenyl)-9,9′-spirobi[9H-fluorene]-2,2′,7,7′-tetramine, Spiro-OMeTAD 2,9-Dimethyl-4,7-diphenyl-1,10-
phenanthroline, BCPphenyl-C61-butyric acid methyl ester
Buckminsterfullerene
26
(a)
(b)
(c)
(1)- Ionic Samples
➢ KCl and LiClO4 solution➢NaCl+ AgNO3 solution➢PSS➢ Nafion➢PbI2 and CH3NH3PbI3
(2)- Dye-Sensitized Solar Cell
DSSC
27
28
Schematic representation of experimental setup used for noise spectroscopy
29
Solvent: Dimethylformamide (DMF)
30
Noise power spectrum density vs frequency plot for PbI2 in DMF solution
Noise power spectrum density vs frequency plot for CH3NH3PbI3 in DMF solution
Voc (V) Isc( A) Jsc mA/cm2 Imax( A) Vmax( V) Pmax mW Fill Factor Efficiency
0.669362 0.012236 2.447203 0.009858 0.533374 5.257901 64.1965 1.0516
31
Noise spectrum obtained from a typical DSSC cell
32Noise contribution from the ions is expected
of 0.6 V was Biasapplied for 60 s prior to illumination
Bias of (-1.2) V was applied for 60 s prior to illumination
Change in noise spectrum with variation in the device history
Time series data of three different structure under dark and light. (a)FTO/ TiO2/ CH3NH3PbI3/Spiro-OMeTAD/Ag (b) FTO/ C60/ CH3NH3PbI3/Spiro-OMeTAD/Ag (c) FTO/Poly-TPD/ CH3NH3PbI3/PCBM/BCP/Ag. The time duration for the capture of one data frame is 0.5 second and 80 frames in each dataset
33
Apoorva Singh, Suman Banerjee, Pabitra Nayak, Zhipping Wang, Jacob Wang H.J. Snaith and K.S. Narayan, Insights in to the microscopic and degradation processes in hybrid perovskite solar cells using noise spectroscopy and photocurrent scanning (Solar RRL – Wiley 2017)
Devices Standard deviation
Device 1 1.8 × 10−8
Device 2 8.4 × 10−9
Device 3 2.8 × 10−9
Representative image from a typical device, showing a linear dependence of Jsc on Intensity
The light intensity serves as a useful parameter to evaluate the transport process of the photo generated carriers
34
power spectrum density (PSD) SI(f) for different intensity/Jsc plotted against f.
J-V characteristics in forward
and reverse scan
FTO/ TiO2/ CH3NH3PbI3/spiro-OMeTAD/Ag
FTOTiO2 (ETL)
PerovskiteSpiro-MeOTAD (HTM)
Ag
35
Normalized power spectrum density ((S(f)), indicating a universal behavior and unified noise value at zero frequency.
Distribution function of current amplitude fluctuation histogram under dark and different intensities (Jsc values) of white light
FTO/ TiO2/ CH3NH3PbI3/spiro-MeOTAD/Ag
36
FTOTiO2 (ETL)
PerovskiteSpiro-MeOTAD (HTM)
Ag
J-V characteristics in forward and reverse scan
Power spectrum density (PSD) SI(f) for different intensities/Jsc
plotted against frequency
FTO/ TiO2/ C60/CH3NH3PbI3/spiro-OMeTAD/Ag
37
Normalized power spectrum density S(f)=(SI / I β(Hz)), unified noise behavior is seenat zero frequency.
Distribution function of current amplitude fluctuation histogram under dark and different intensities (Jsc values) of white light 38
FTO/ TiO2/ C60/CH3NH3PbI3/spiro-OMeTAD/Ag
FTO/Poly-TPD/CH3NH3PbI3 /PCBM/BCP
FTOPoly-TPD (HTM)
PerovskitePCBM (ETL)
BCP (ETL)Ag
39
J-V characteristics in forward and reverse scan
PSD at different intensities/Jsc values, device at the measurement had PCE of ~15%
PSD measured from the device, cell degradeddown to PCE of <0.1%. 1 to 5 represents intensities(0.45 mW/cm2, 9.8 mW/cm2, 18.6 mW/cm2, 23mW/cm2, and 52.4 mW/cm2).
Normalized power spectrum density S(f)= (SI / I β(Hz))
FTO/Poly-TPD/CH3NH3PbI3 /PCBM/BCP
40
FTOPoly-TPD (HTM)
PerovskitePCBM (ETL)
BCP (ETL)Ag
Parameters Device 1 Device 2 Device 3
FTO / TiO2 /
CH3NH3PbI3 / Spiro-
OMeTAD / Ag
FTO / C60 / CH3NH3PbI3 /
Spiro-OMeTAD / Ag
FTO /Poly-TPD /
CH3NH3PbI3 / PCBM /
BCP / Ag
Voc ( V) 0.91 0.88 1.04
Jsc
( mA/cm2)
16.51 2.61 21.85
Fill Factor 48.78 60.67 69.9
Efficiency
(η %)
7.32 1.39 15.96
α in 1/fα α~ 1.9
α~ 2 for lower f (<100Hz)
and α~1 for higher f.
At very low η (<0.1%),1/f is
uniform with α~ (1to 1.4)
α~ 1. In addition to
1/f,
G-R noise is observed.
at η <0.1%, uniform
1/f behavior with α~1
β in Iβ ~ (2 to 2.5) ~ 1.6 ~2
Summary of performance and noise parameters from representative devices of each structure.
41
FTO/Poly-TPD/CH3NH3PbI3 /PCBM/BCP
42
Degradation studies: (a) J-V curve for different degradation stages (b)corresponding normalized noise power spectrum density (NPSD), S(f). η of15.96%, 7.83%, 4.57% and <1% corresponds to the measurements taken at 0 hr.,8 hrs., 16 hrs. and 32 hrs. respectively.
FTOPoly-TPD (HTM)
PerovskitePCBM (ETL)
BCP (ETL)Ag
Background for Admittance Studies
• An electrically active defect reveals itself as a peak in the conductance G versus temperature T
• Peak in G/ω versus frequency ω curves
• as a step in the capacitance C versus T or C versus ω curves.
• A relation between the defect density of states and the frequency derivative of capacitance ωdC/dω versus ω - Walter et al (1196 JA. ApplPhys.)
44
Mott-Schottky plot for perovskite solar cells. The blue
line is an extrapolation to determine the built-in voltage.
Vbi (V) Nd (cm-3) W (cm)
Fresh 0.95 5.6x1015 7.5x10-5
Aged 0.87 8.6x1016 1.8x10-5
The slope of the extrapolation can be
used to determine the doping density Nd
depletion width W at Vbias = 0 V
TAS
45
a) Typical temperature dependence of the frequency-dependent
capacitance of a perovskite solar cell. b) Arrhenius plot of the
characteristic transition frequencies extracted from a) to extract the
defect activation energy of a perovskite solar cell.
the trap energy Ea and
the characteristic
transition frequency ω0
can be expressed as:
TAS
46
: tDOS for perovskite solar cells before and after aging.
the frequency dependent
capacitance can be used to
determine the energetic
profile of the tDOS
The resultant graph shows the tDOS as a function of energy related to the
valence band of the perovskite. These graphs have been extracted from
multiple devices. Integration of the tDOS along the horizontal axis gives the
trap density in the perovskite.
Trap density evaluation using TAS
Experiments performed by Dr. Zhipping Wang and Dr. Pabitra Nayak, Prof. Snaith’s Lab, Univ. of Oxford (U.K.)
Evolution of noise spectrum with degradation as seen in conventional structure of hybrid perovskite solar cells
FTO/TiO2/ C60/ CH3NH3PbI3/spiro-OMeTAD/Ag
47
➢ Noise magnitude relative to the signal directly correlates
with the performance parameters, with the noise levels
increasing with degradation.
➢ All the devices exhibit 1/fα behavior in the range < 1 kHz
➢ The exponent α and f range over which 1/f response is
observed appears to depend on the transport processes
and the associated disorder in the system.
➢ the noise mechanism of devices under operation with
high J (at high light intensity) is different from that at low
J.
➢ This intensity dependent noise response appears to be
dependent on the device structure and is different from
the different geometry.48
Introduction…………
Generation:
• Photoactive metal/polymer schottky interface
• External electric field
• Excitation wavelength of light
Transport:
● Poisson’s Eqn ● Current Density Eqn ● Continuity Eqn
2
2
0
x
nD
x
nE
x
En
nnG
t
n p
n
p
nnp
n
pp
n
p
mm
Generation &
Recombination RateDrift Diffusion
r
ITO
stri
p
PolymerAl
holes
laser
r
h+
r
ITO
stri
p
PolymerAl
holes
laser
r
h+
LPE: A non- uniform illumination of schottky (or p++ - n / p – n++ junction)
interface compensate built- in barrier field locally, which results in a lateral
photo-electric field in the plane of interface
Ln=(Dnn)1/2
x
np(x)
np0
)exp(0 00 npppp Lxnnnxn
0
2
1
21 .
.
e
tTktDr nB
n
m
Einstein Relation: Dn = mnkBT/e ?
2
2
0
x
nD
x
nE
x
En
nnG
t
n p
n
p
nnp
n
pp
n
p
mm
Introduction…………
Diffusion Process: Carrier Transport Studies
Al
Polymer
laser
electronsr
ITO
r
e-
Al
Polymer
laser
electronsr
ITO
r
e-
r
e-
E = 0
Low intensity
Steady State (dn/dt = 0)
μτe
TkL
)Lr( exp 0nrn
B2
d
d
Ld=(D)1/2r
n(r)
n0
Materials
Semiconducting polymers:
O
O
n
S
S
S
S
Poly(3-hexylthiophene) (P3HT)
Poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-
phenylene vinylene) (MEHPPV)
Poly(9,9-dioctylfluorene-alt-bithiophene) (PFO - TT)
**
nS
S
S
S
S
S
Materials………
P3HT
➢ Orientation on Hydrophobic Surfaces (HMDS, APS and OTS)
➢ Micro-nano crystalline domains
➢ 2D lateral transport (Interchain & intrachain hopping)
➢ High hole mobility
O
O
n
Materials…………
MEHPPV
➢ Disorder system
➢ Conformational configuration of phenyl rings
➢ Random flexible coiled polymer chains
➢ Poor carrier mobility
Materials…………
PFO – TT
➢ Nematic liquid crystalline phase
➢ Spatially anisotropic electric transport
➢ Higher mobility in oriented direction
➢ Ambipolar behavior in oriented samples
ry
rubbed direction || to rx
PFO – TT chainsry
rubbed direction || to rx
PFO – TT chains
**
nSS
Experiments……….(Spatial Dependence)
(b)
SEM
Scanning Probe Photocurrent Contrast Image
Photocurrent Profile
Photocurrent
Cover glass
ITO strips
Al
60X
polymer
Cover glass
ITO strips
Al
60X
polymer
(a) 5 mm
32.80 pA
31.60 pA
(c)
(b)
ITO
31.10 pA
33.65 pA
31
32
33
34
0 10 20 30
r(mm)
I light(p
A)
Experiments……….(Spatial Dependence)
Al
Polymer
laser
electronsr
ITO
r
e-
Al
Polymer
laser
electronsr
ITO
r
e-
r
e-
r
ITO
stri
p
PolymerAl
holes
laser
r
h+
r
ITO
stri
p
PolymerAl
holes
laser
r
h+
0
50
100
0 40 80 120
electrons
holes
Ilig
ht(n
orm
.)
0
50
100
0 5 10 15
electrons
holes
electrons
holes
Ilig
ht
0
50
100
0 10 20 30
r (mm)
I lig
ht
O
O
n
S n
**
n
S
S
C8H17C8H17
(b)
(c)
(d)
Scanning Directions
1. Ldh(rx)
2. Lde(rx)
3. Lde(ry)
4. Ldh(ry)
PFO-TT
ITO
Rubbed Polyimide
12
3
4
rx
ry
|| to rx
|| to ry
Light Polarization Dependence
Experiments……….(Spatial Dependence)
20
40
60
80
100
0 200 400 600
holes
rx
ry
r mm)
I ligh
t (n
orm
. u
nits)
0
50
100
0 60 120 180
electrons
ry
rx
r (mm)
I ligh
t
ry
rubbed direction || to rx
PFO – TT chainsry
rubbed direction || to rx
PFO – TT chains
Structurally Induced Electrically Anisotropic Charge Carrier Transport
Results
Polymer decay length
(Lde) from Ile(r)decay length
(Ldh) from Ilh(r)mhh/mee
P3HT 8.3 mm 51.1 mm 37.54
MEHPPV 2.8 mm 6.8 mm 5.96
unoriented PFO
– TT
3.9 mm 14.1 mm 13.07
PFO – TT (rx)
polarization || to
rx
87.3 mm 134 mm 2.36
PFO – TT (ry)
polarization || to
rx
25.5 mm 50.3 mm 3.89
Decay lengths for electrons (Lde) and holes (Ldh)
Kabra and Narayan Adv. Mat. 2008
Wd
qVbi
EF
HOMO
LUMO
+
-
Al P3HT
Wd
qVbi
EF
HOMO
LUMO
+
-
Al P3HT
Wd
qVbi
EF
HOMO
LUMO
++
--
Al P3HT
D. Kabra et al. Appl. Phys. Lett. 85, 5073, 2004.
Polymer / Al schottky interface
Net lateral photovoltage
X
ph(x)
Depletion layer
AuL AuR
Light
Polymer
L / 2 L / 2
Al
Introduction…………(LPE)
RL
Polymer
L
Polymer
L = R
- -
+++
++
-
+ ++
--- - - - - - -- --- - - - - - - --
+++
+
-
+ ++
+
R
L > R
phL phR
Al
Polymer
Chopped
laser
L
w
Device Fabrication…………
(i)
(ii)
(iii)
(iv)
(vi)
(vii)
Substrate
(Glass)
Physical Shadow Mask
Metal (Cr - Au) Deposition
Polymer Coating
(Spin coating)
Physical Shadow Mask
Metal (Al) Deposition
10 mm
1 mm
De
w
700 nm
Model
Polymer/Al schottky interface
(0,0) (0,1) (0,2)
(1,2)
(2,2)
Iph
Rsp01
Csp01
Ct
Ct
Ct
CtCtCt
Ct = Transverse Capacitance
Rsp= Spreading Resistance
Csp= Spreading Capacitance
Cell Size = 10 mm
Experiments……….(Spatial Dependence)
controller
50 X 633 nm
543 nm
10X
Interface box
Lock-inx
Lock-in
PD
PSD
1D Optical Profiling Setup
Experiments……….(Spatial Dependence)
Solar cell
type
PSDs
Lateral photovoltage- in Hybrid Perovskites
ΔVp
h
)(xph
x
L/
2
L/
2Au Au
Glass
MAPbI3 Depletion
layer
x=0
mm x=L
mm
Light
ehe
e
ee e e e e e e e ee IT
O
L > R
h
h h
)(xph x
L/
2
L/
2Au Au
Glass
x=0
mm x=L
mm
Light
ehe
e
ee e e ee e e ee IT
O
L < R
h
h h
e
MAPbI3
ΔVphφL
φR φLφR
Page 26
Light
Experimental Setup
Page 27
(a
)
xy
Glass
Vph1
, Lock-in Amplifier21)( phphph VVxV
Vph2
AuAu
50X
0.70 NA
(b
)
Light
ΔVp
h)(xph
x
ITO
L/2 L/2Au Au
Glass
MAPbI3
Depletion layer
x=0 mm x=3
mm
Chapter 4
ΔVph(x)=differential lateral photo voltage
Spatial dependence of differential lateral photo voltage - I
Page 28
A
u
A
u
ΔV
ph
(mV
)
(a
)
ΔV
ph
(mV
)
(b
)
Chapter 4
Spatial dependence of differential lateral photo voltage - II
Chapter 4
Page 29
Transient response of PSD
light
Oscilloscope
Au
Au
𝐼 = 𝐼0exp(−𝑡
𝜏)
τ= 43 µs
Page 30
τ, independent of beam position
❖ Demonstrated position sensing devices (PSD) based on a simple geometry using active
HOIP layers.
❖Linear response of the differential signal covering a wide wavelength range at reasonable bandwidth
❖High spatial resolution, and large length span is demostrated.
❖2 µV/µm spatial resolution is an order higher than analogous polymer based PSD structure and the position resolution is comparable to commercial PSDs
Chapter 4
Page 31
Ashar, Ganesh and Narayan Adv. Elec. Mat. 2017
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Experimental Setup
75
Results from the photocurrent scanning along with transmittance of two different devices.Variations in the photocurrent response (indicated by color contrast)
76Ingress of moisture and oxygen happens from the periphery
(a)
(b)
77
D1
D2
D3
D4
D5
D6
D7
1 2 3 4
2-D photocurrent scanning for 4 𝑚𝑚 × 4 𝑚𝑚 area with a beam size of ~10 µm and intensity 1mW/cm2.The regions of different photocurrent can be seen with the color contrast. Figure shows device degradation with time.
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Apoorva Singh, Suman Banerjee, Pabitra Nayak, Zhipping Wang, Jacob Wang H.J. Snaith and K.S. Narayan, Insights in tothe microscopic and degradation processes in hybrid perovskite solar cells using noise spectroscopy and photocurrent
scanning (Solar RRL 2017)
79
➢ Perovskite-based solar cells exhibit characteristic noise features.
➢ The magnitude of the fluctuations and the associated PSD response directly correlates to the state of the device.
➢ Devices with inverted structure were found to be most stable against the illumination in the present studies.
➢ Noise measurements along with a suitable model appear to be a valuable tool to evaluate the defect characteristics.
➢ These studies are useful and relevant in gauging the feasibility of hybrid perovskite-based cells.
Th. B.SinghA.G.ManojDinesh KabraDhritamn GMonojit BagSabyasachi M.Anshuman DSatyaprasadRavichandranV. VijayPrashanthVini GautamRishav HarshKishore C
Prashant KSwatiRaageshAsharAnaranya
GaneshApoorva SinghSuman BAbdul
Funding: JC Bose Fellowship Grant, Indo-UK APEX
Anil KumarSridhar RajaramSatish PatilSanjio ZadeParameswaran IyerT.G.RajuAsha ShyamaJames DurrantA. FachettiT. Marks
Henry SnaithR. H. FriendSuby GeorgeSatish Ogale