Complementary techniques to investigate degradation mechanisms in solar cells Simon Züfle a,b , Martin Neukom a , Beat Ruhstaller a,b 10.09.2015 a: Fluxim AG, Winterthur, Switzerland b: Institute of Computational Physics, ZHAW, Winterthur, Switzerland
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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
Who we are
2
Sim
ula
tion S
oft
ware
Me
asu
rem
ent
Ha
rdw
are
Research on
OLED and OPV
Stability of Solar Cells
11.09.2015 3
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
4
Impedance
Spectroscopy
Capacitance-Voltage
Dark Injection Transients
Transient Photocurrent
Photo-CELIV
Transient Photovoltage
IV-Curves
Techniques we propose:
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
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
Preconditioning -1V Preconditioning +1V
Repeated Transient Photocurrent on Perovskite SC
Stress-Test Module
Evidence for movement of ionic charges
11.09.2015 8
• 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
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)
Accelerated Ageing Study
11.09.2015 10
• 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
Steady-State Measurements
11.09.2015 11
-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!
11.09.2015 12
-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
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
11.09.2015 13
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
-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
11.09.2015 14
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
Conclusions
11.09.2015 15
• 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
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
11.09.2015 16
Acknowledgement
Simon
Züfle
Beat Ruhstaller
Stephane
Altazin
Martin
Neukom
Adrian
Gentsch
Thank you for your attention!
Transient Photovoltage
DSC
Perovskite Organics
CdTe
P3HT:CdSe
Drift & Diffusion Traps
Recombination Ions?
Leakage Current
Capacitance-Voltage
Injection barriers Doping
Built-in voltage
DSC
Perovskite
P3HT
uc-Si
23
Perform all experiments at temperatures
from 150 to 350 K
Low Temperature Module
CELIV TPC
Transient and ac Measurements
11.09.2015 25
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!