Supplemental Information: Mechanisms for Light
Induced Degradation in MAPbI3 Perovskite Thin
Films and Solar Cells
Ghada Abdelmageed1, 2§, Leila Jewell3§, Kaitlin Hellier3, Lydia Seymour3, Binbin Luo2, 4,
Frank Bridges3, Jin Zhang2, and Sue Carter3*
1
Department of Radiation Physics, National Center for Radiation Research and
Technology (NCRRT), Atomic Energy Authority (AEA), Nasr City, Cairo, 11787, Egypt.
2
Department of Chemistry and Biochemistry, University of California, Santa Cruz,
California 95064, United States.
3
Department of Physics, University of California, Santa Cruz, California 95064, United
States.
4
College of Chemistry and Chemical Engineering, Chongqing University, Chongqing
400044, China.
1
Previous light-induced degradation studies on perovskites imply that the UV content of
the light is the main reason for the perovskite’s destruction, so we tested the stability of
MAPbI3 with an encapsulant that prevented UV light.1 The encapsulatant used was
aliphatic polyurethane (TPU), which contained added UV absorbers. Figure 6 shows a
depiction of the MAPbI3 sample with the TPU encapsulation layer, the UV-Vis
absorbance spectrum of the TPU showing UV cutoff around 400 nm, and the UV-Vis
absorbance spectra of the MAPbI3 film encapsulated by TPU. The absorbance data
clearly shows that light below the UV region (λ > 400nm) is capable of destroying
MAPbI3 completely, turning it from the dark brown color to the bright yellow color of
PbI2.
Figure S1 The degradation of MAPbI3 films with TPU encapsulation. (a) Illustration of
the experimental setup of the aging process of perovskite with the application of the TPU
layer. (b) The UV-Vis absorbance spectrum of the TPU showing cutoff edge around 400
nm. (c) The UV-Vis absorbance spectra of MAPbI3 films encapsulated with TPU and
exposed to light in dry air.
2
Figure S2, The FT-IR spectra of MAPbI3 films before and after 28 days of storage in dark
dry conditions.
Figure S3 The FT-IR of MAI before and after illumination. The spectra show significant
decrease in the N-H bands in the range 3000cm-1 - 3500cm-1, which shows a
deprotonation process.
3
For the device stability experiment: The solar cell devices were prepared layer by layer
as in Figure S4. Pre-patterned ITO slides were used, then a TiO2 sol gel dense layer and
mp-TiO2 nanoparticles layer were each spin-coated, respectively. Each TiO2 layer was
sintered at 450 °C for 30 min in air. MAPbI3 layer prepared by two steps methods
reported elsewhere.2 For the Hole transport Layer (HTL), Poly (3-hexylthiophene-2,5diyl) (P3HT) with concentration of 10 mg/ml in was spin-coated on the perovskite layer
with speed of 2000 rpm for 60 s. Finally, 80 nm of gold contact was thermally evaporated
under high vacuum. The performance of the devices was tested at different conditions
such as with light in dry air and N2 filled environment with and without TPU layer (figure
S4) and in dark with dry air. The area reported of each device formed is 0.03 cm2. Current
2
density-voltage (J-V) curves were taken under one sun illumination (100 mW/cm ) at
calibrated AM1.5G condition.
Figure S4 Device structure of MAPbI3 solar cells subjected to light with and without TPU
UV blocking layer.
The device parameters are listed in table S1 and the JV characteristics are plotted in
Figure S5. It is clear that the device stored in dark dry environment has the least decrease
4
in the device parameters (about 10% loss in the original values). Since perovskite films
show no degradation in dark dry environment, it is probable that this change in the device
values is due to the gold ion migration through the hole transport layer (HTL).5 Devices
subjected to light in dry air have degraded and lost almost 99% of its initial efficiencies
after 1 day. These results were expected since we have noticed the fast degradation of
perovskite in the presence of both light and oxygen. However, although perovskite films
subjected to light in N2 filled environment did not show any signs of degradation, the
performance of the perovskite solar cell in the same condition was not stable. The device
without UV protection (no TPU) has lost 95% of its initial efficiency after 7 days of
continuous illumination; meanwhile, the device with UV blocking layer has lost about
35% of its initial efficiency. This gives a 60% difference in the efficiency loss between
the two devices, which stems from the UV light induced interfacial degradation at the
mpTiO2/MAPbI3 interface. The loss in the PCE of the device with TPU may be due to the
heat coming from the lamp, which can reach ~55ºC.
5
Table S1 Solar cell parameters of devices aged in several conditions
0 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
1 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
2 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
3 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
4 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
5 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
6 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
7 Day(s)
Jsc (mAcm-2)
Voc (V)
FF (%)
PCE (%)
N2
(W\TPU)
N2
(W\O TPU)
Dry air
(Dark)
Dry air
(W\TPU)
Dry air
(W\O TPU)
22.9
0.87
48.6
9.81
24.7
0.92
40.4
9.04
24.2
0.91
42.0
9.29
23.9
0.89
44.7
9.43
24.3
0.93
48.8
9.29
23.7
0.84
48.4
9.69
17.5
0.79
42.3
5.81
22.5
0.94
47.5
9.30
2.05
0.18
25.7
0.09
2.07
0.32
25.9
0.17
23.1
0.82
46.3
8.89
13.9
0.72
42.6
4.31
22.7
0.92
43.9
9.16
-
-
22.4
0.82
45.7
8.41
11.2
0.66
36.1
2.62
24.5
0.84
42.5
8.77
-
-
23.0
0.78
45.8
8.25
9.11
0.57
36.4
1.92
23.5
0.85
43.5
8.74
-
-
21.3
0.78
43.0
7.17
8.94
0.44
30.5
1.19
23.9
0.89
38.8
8.34
-
-
20.2
0.79
42.9
6.88
5.09
0.44
32.7
0.72
21.6
0.83
46.2
8.26
-
-
19.01
0.78
41.7
6.11
4.01
0.37
36.3
0.54
22.5
0.83
43.1
8.11
-
-
6
Figure S5 The J-V characteristics of mp-TiO2/MAPbI3 solar cells aged in different
conditions: (a) With light in N2 with TPU, (b) with light in N2 without TPU, (c) with light
in dry air with TPU, (d) sith light in dry air without TPU, (e) stored in dark dry condition.
7
XRD analysis: The light induced destruction of the MAPbI3 crystal structure was
monitored by XRD as shown in Figure S6. From the data, we confirm the perovskite
formation in the fresh films, observing peaks at 14.126°, 28.467°, 31.844° and 40.55° that
correspond to (001), (002), (301) and (242) diffraction peaks, respectively. These data
indicate the orthorhombic structure of the perovskite with lattice parameters of a = 12.62
Å, b = 26.66 Å and c = 8.90 Å. It can be noted that the fresh MAPbI3 on mp-TiO2 had a
remnant unconverted hexagonal PbI2 (~7 wt.%), shown by a peak at 2θ = 12.5° that did
not exist in the mp-TiO2 free samples (100% MAPbI3). 3 It is possible that the mp-TiO2
prevents some of the infiltrated PbI2 from reacting with the methyl ammonium iodide
solution in the dipping step of perovskite formation. This result is expected due of the
nature of the preparation method, which is based on depositing a dense layer of PbI2 and
then converting it to perovskite by introducing a solution of the organic cation. As seen
from Figure S4, after one day of aging perovskite, the material becomes partially
degraded and the PbI2 content increases to ~ 40 wt.% and ~ 20 wt.% in samples with and
without mp-TiO2, respectively, which indicates a mixture of PbI2 and MAPbI3 structures
present. After one week of exposure, the MAPbI3 is fully degraded into hexagonal PbI2.
In contrast, the samples kept in dark showed no increase in the PbI2 content and remained
at 100 wt.% of pure perovskite. An interesting note is that the MAPbI3 kept in the dark
for a week with mp-TiO2 went from orthorhombic to cubic crystal structure. The change
may be due to the influence of chlorine present in CoCl2, which is a common color
indicator in the desiccant material that we used to keep a moisture free environment. This
is in agreement with a previous study that found the phase transition temperature of
8
MAPbI3 to cubic structure (54°C) could be significantly reduced to room temperature in
the presence of chlorine.4
Figure S6 X-ray diffraction patterns of MAPbI3 after 0, 1, and 7 days in a dry air. (a)
XRD spectra of illuminated mp-TiO2/MAPbI3 (b) XRD spectra of illuminated MAPbI3
only, (c) XRD spectra of mp-TiO2/MAPbI3 kept in dark (b) XRD spectra of MAPbI3 only
kept in dark. The spectra show the transformation of MAPbI3 to PbI2 with illumination.
PbI2’s peak at 2θ = 12.5° is marked by *.
9
Figure S7 Fit of the Pb LIII edge data on the thin film of partially degraded MAPbI3 on
mp-TiO2. The fit used a sum of the functions shown in Fig 4 (for fresh MAPbI3 (no mpTiO2)
10
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