Complementary techniques to investigate degradation ... · Complementary techniques to investigate...
Transcript of Complementary techniques to investigate degradation ... · Complementary techniques to investigate...
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Complementary techniques to investigate degradation mechanisms in solar cells
Simon Züflea,b, Martin Neukoma, Beat Ruhstallera,b
10.09.2015
a: Fluxim AG, Winterthur, Switzerland b: Institute of Computational Physics, ZHAW, Winterthur, Switzerland
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Who we are
2
Sim
ula
tion S
oft
ware
Me
asu
rem
ent
Ha
rdw
are
Research on
OLED and OPV
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Stability of Solar Cells
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How to characterize and compare stability? Standardization! - IEC 61215 for c-Si - IEC 61646 for thin-film - ISOS Protocols for OPV But: focussed on steady-state, where valuable information on degradation is concealed.
Reese et al., Solar Energy Materials and
Solar Cells, (2011), 95, 1253
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Impedance
Spectroscopy
Capacitance-Voltage
Dark Injection Transients
Transient Photocurrent
Photo-CELIV
Transient Photovoltage
IV-Curves
Techniques we propose:
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t
Light
t
Current
• Cell is flashed at constant
voltage
• Qualitative investigation of
charge carrier mobility
• Qualitative investigation of
trapping dynamics
Transient Photocurrent TPC
Isc
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DSC
Perovskite OPV
CdTe
P3HT:CdSe
Hybrid
Drift & Diffusion Ionic movement
Traps Other slow effect? Space-charge effects due to doping
µc-Si
Transient Photocurrent: Technology Comparison
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Preconditioning -1V Preconditioning +1V
Repeated Transient Photocurrent on Perovskite SC
Stress-Test Module
Evidence for movement of ionic charges
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• Drift-Diffusion Simulation
• Simulate all experiments with one set of parameters
• Modeling helps to understand device physics
• Get further insight into device
Neukom et al., Org. El. 13,2910 (2012)
Modeling
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IV
dark-CELIV
TPC
photo-CELIV
Measurement
and simulation
of an organic
solar cell
Global fit with
one set of
parameters!
Advanced Characterization Example
Neukom et al., Org. El. 13,2910 (2012)
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Accelerated Ageing Study
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• Standard unencapsulated P3HT:PCBM organic solar cells with PEDOT:PSS as hole transport layer (unstable)
• In climate chamber at 45°C, 85%RH investigate influence of humidity
• Automated repetition of measurement routine
Highly systematic data!
P3HT:PCBM
PEDOT:PSS
Aluminum
ITO
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Steady-State Measurements
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-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-10
-5
0
5
10
15
20
Voltage (V)
Curr
ent
density (
mA
/cm
2)
0 min
5 min
12 min
24 min
37 min
49 min
61 min
73 min
85 min
96 min
108 min
0 50 1000
0.2
0.4
0.6
Deg time (min)
Voc (
V)
Current-Voltage
0 20 40 60 80 100 1200
1
2
3
4
5
Degradation time (min)
Jsc (
mA
/cm
2)
Short-circuit current
No conclusions about degradation mechanism possible!
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-1 -0.5 0 0.5 1 1.50
50
100
150
Voltage (V)
Capacitance (
nF
/cm
2)
0 min
5 min
12 min
24 min
37 min
49 min
61 min
73 min
85 min
96 min
108 min
Hypothesis: Insulating Al2O3 interface layer grows, leading to MIS structure.
Cell B Cell B Cell A
Al2O3 Al2O3
Glass Substrate
PEDOT:PSS
P3HT:PCBM
Al
ITO
AC Measurements
-1 -0.5 0 0.5 1 1.5 20
20
40
60
80
100
120
140
160
180
200
Vdev (V)
capacitance (
nF
/cm
2)
Sim, x = 0, fresh
Sim, x = 0.42
Sim, x = 0.57
Sim, x = 0.91
Sim, x = 1, degraded
Capacitance-Voltage
Simulation of growing MIS
Surface A: (1-x)·Sini Surface B: (x)·Sini
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0 10 20 30 40 50 60 70 80 90
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2
Time (us)
Curr
ent
density (
mA
/cm
2)
0 min
5 min
12 min
24 min
37 min
49 min
61 min
73 min
85 min
96 min
108 min
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t
Lig
ht
Transient Measurements Transient Photocurrent
0 20 40 60 80 100
0
2
4
6
8
10
12
14
16
18
time (us)
J (
mA
/cm
2)
x = 0
x = 0.39
x = 0.55
x = 0.67
x = 0.77
x = 0.87
x = 0.95
«There is life after death!»
Charge extraction is hindered:
Blocking Al2O3 layer
Simulation
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-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-10
-5
0
5
10
15
20
Voltage (V)
Curr
ent
density (
mA
/cm
2)
Exp, t = 0 min
Exp, t = 5 min
Exp, t = 37 min
Exp, t = 102 min
Sim, x = 0, fresh
Sim, x = 0.42
Sim, x = 0.68
Sim, x = 0.94
Sim, x = 1, degraded
Comparison
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Model-based analysis helps to quantitatively validate the postulated degradation mechanism!
IV: Paios Measurements + Setfos Simulations
x describes effective area vs time, in agreement
with a 2D diffusion model
Electric field at short-circuit
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Conclusions
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• Hypothesis: Al2O3 layer acts as insulating interface resulting in a local complete loss of current
Lateral instead of homogeneous degradation process!
This conclusion is possible without time-consuming, expensive and destructive methods!
Züfle et al., Adv. En. Mater., 2015, in press, 10.1002/aenm.201500835
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Summary
• IV-curves alone are not enough to understand degradation processes
• Transient and impedance techniques reveal valuable information
• Systematic measurement data allows for combinatorial analysis
• Advanced Modeling helps to validate hypothesis and gives additional insight into the device
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Acknowledgement
Simon
Züfle
Beat Ruhstaller
Stephane
Altazin
Martin
Neukom
Adrian
Gentsch
Thank you for your attention!
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Transient Photovoltage
DSC
Perovskite Organics
CdTe
P3HT:CdSe
Drift & Diffusion Traps
Recombination Ions?
Leakage Current
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Capacitance-Voltage
Injection barriers Doping
Built-in voltage
DSC
Perovskite
P3HT
uc-Si
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Perform all experiments at temperatures
from 150 to 350 K
Low Temperature Module
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CELIV TPC
Transient and ac Measurements
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0 5 10 15
-30
-25
-20
-15
-10
-5
0
Time (us)
Curr
ent
density (
mA
/cm
2)
0 50 1000
2
4
6
8x 10
22
Deg time (min)Extr
acte
d c
harg
es (
1/m
3)Photo-CELIV
Dark-CELIV
0 10 20 30 40 50 60 70 80 90
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
2
Time (us)
Curr
ent
density (
mA
/cm
2)
0 min
5 min
12 min
24 min
37 min
49 min
61 min
73 min
85 min
96 min
108 min
-1 -0.5 0 0.5 1 1.50
50
100
150
Voltage (V)
Capacitance (
nF
/cm
2)
0 min
5 min
12 min
24 min
37 min
49 min
61 min
73 min
85 min
96 min
108 min
104
105
106
0
5
10
15
20
25
30
35
40
Frequency (Hz)
Capacitance (
nF
/cm
2)
0 min
5 min
12 min
24 min
37 min
49 min
61 min
73 min
85 min
96 min
108 min
C-V C-f
Systematic data of the same device during degradation!
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Combinatorial Analysis
• Electrode workfunctions are constant
• Electrode resistance is constant
• Layer thickness is constant
• No doping is present
• Traps cannot be dominant mechanism
• Absorption loss cannot be dominant mechanism
• Decreased mobility cannot be dominant mechanism
• Space charge due to hampered extraction
There is life even in dead cells!
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