SUPPORTING INFORMATION

Highly efficient and stable planar perovskite solar cells by solution-processed tin oxide

Elham Halvani Anaraki1,2; Ahmad Kermanpur2; Ludmilla Steier3; Konrad Domanski3; Taisuke Matsui4; Wolfgang Tress3; Michael Saliba3; Antonio Abate3,5; Michael Grätzel3; Anders Hagfeldt1*; Juan-Pablo Correa-Baena1*

1Laboratory of Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1015-Lausanne, Switzerland.

2 Department of Materials Engineering, Isfahan university of Technology, Isfahan, 84156-83111, Iran.

3Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1015-Lausanne, Switzerland.

4Advanced Research Division, Panasonic Corporation,1006, (Oaza Kadoma), Kadoma City, Osaka 571-8501, Japan.

5Adolphe Merkle Institute, University of Fribourg, CH-1700 Fribourg, Switzerland.

*Corresponding authors: AH, anders.hagfeldt@epfl.ch ; JPCB, juan.correa@epfl.ch.

Keywords: Perovskite solar cell, metal oxide semiconductors, electron selective layers, stability, SnO2.

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Electronic Supplementary Material (ESI) for Energy & Environmental Science.This journal is © The Royal Society of Chemistry 2016

Note 1:

Optimization of solution processed SnO2 layers.

In order to improve the reproducibility of the deposition of the layers, two additional

procedures were tested. A third method, involved solely the chemical bath deposition in a

diluted form (CBD-d) as shown in Figure 1b. Finally, a method using spin coating and a

dilute version of the chemical bath (SC-CBD-d) was used to optimize this layer. The

properties of these films and their respective devices will be discussed throughout the

supporting information.

2

200 nm 400 nm

200 nm 400 nm

a b

c 200 nm 400 nm

200 nm 400 nm

d

e

200 nm 400 nm

f 200 nm 400 nm

Figure S1. Top view SEM images of different ESL deposition methods. a. ALD , b. spin coated SnO2 (SC), c. spin coated SnO2 and chemical bath post-treatment (SC-CBD), d. chemical bath only (CBD), e. spin coated SnO2 and dilute chemical bath post-treatment (dilute SC-CBD) deposited on FTO as ESLs, and (f) Bare FTO. All micrographs in two different magnifications.

3

20 30 40 50 60 70 80

SCCBD-d

CBD-d

SC-CBD

Inte

nsity

/ a.

u.

2-Theta / degree

FTO

SC

Figure S2. Structural features of the different ESLs. XRD patterns of bare FTO, spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-treatment (SC-CBD), dilute chemical bath only (CBD-d), spin coated SnO2 and dilute chemical bath post-treatment (SC-CBD-d), deposited on FTO as ESLs

4

695 690 685 680Binding Energy / eV

F1s scan

Cou

nts

/ a.u

.

SCCBD-d

CBD-d

SC-CBD

SC

1000 750 500 250 0

SCCBD-d

CBD-d

SC-CBD

SC

survey scan

Binding Energy / eV

Cou

nts

/ a.u

.

ALD

536 534 532 530 528

O1s scan

Cou

nts

/ a.u

.

Binding Energy / eV

SCCBD-d

CBD-d

SC-CBD

SC

ALD

500 495 490 485

Cou

nts

/ a.u

.

Binding Energy / eV

Sn3d scan

SCCBD-d

CBD-d

SC-CBD

SC

ALD

a

c

b

d

Figure S3. X-ray photoelectron spectroscopy of the different ESLs. (a) Survey of elements and their related high resolution spectra of (b) F 1s, (c) Sn 3d and (d) O1s and peaks as a function of their deposition method containing: atomic layer deposited (ALD), spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-treatment (SC-CBD), dilute chemical bath only (CBD-d), spin coated SnO2 and dilute chemical bath post-treatment (SC-CBD-d), deposited on FTO as ESLs.

5

200 nm 400 nm 200 nm 400 nm

200 nm 400 nm 200 nm 400 nm

200 nm 400 nm

a b

c d

e

Figure S4. Morphological features of perovskite films. Top view SEM images of perovskite deposited on: a. ALD , b. spin coated SnO2 (SC), c. spin coated SnO2 and chemical bath post-treatment (SC-CBD), d. dilute chemical bath only (CBD-d), e. spin coated SnO2 and dilute chemical bath post-treatment (dilute SC-CBD). Two different magnifications per sample are shown.

6

500 600 700 8000.0

0.5

1.0No

rmal

ized

Abs

orba

nce,

PL

/ a.u

.

Wavelength / nm

ALD SC SC-CBD CBD-d SCCBD-d

Figure S5. Optical properties of perovskite films. Normalized UV-vis absorption and normalized steady state photoluminescence of perovskite films deposited on: atomic layer deposited (ALD), spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-treatment (SC-CBD), dilute chemical bath only (CBD-d), spin coated SnO2 and dilute chemical bath post-treatment (SC-CBD-d), deposited on FTO as ESLs.

Photoluminescence and UV-visible spectra (Figure S5) of the mixed ion perovskite

material show a narrow peak with the maxima located at 758 nm, and a sharp absorption

onset at ca. 760 nm, respectively.

7

b

c d

a

e

Figure S6. Cross-sectional SEM images for devices using different configurations. a. ALD, b. spin coated SnO2 (SC), c. spin coated SnO2 and chemical bath post-treatment (SC-CBD), d. dilute chemical bath only (CBD-d), e. spin coated SnO2 and dilute chemical bath post-treatment (dilute SC-CBD). The scale bar is 200 nm.

8

Note 2:

Investigation of reproducibility and blocking properties of all layers:

To understand the electron blocking properties and coverage quality of the SnO2 layers

deposited with the different methods, cyclic voltammetry was performed using the

aqueous solution of Fe(CN)63-/4- as the redox couple.1 Cyclic voltammetry was performed

for at least three random samples of each condition and at least three consecutive voltage

scans for each sample to be sure of reproducibility. All deposition methods yielded

sufficient blocking compared to bare FTO as shown in Figure S7a, with SC and SC-CBD

SnO2 films showing some source of leakage. Depositions of SnO2 films with CBD and

the dilute SC-CBD showed perfectly blocking properties. This behavior is also seen in

the dark current-voltage sweeps of full devices, as shown in Figure S7b. Here, the SC and

SC-CBD show more leakage than the ALD controls and the devices treated with the

dilute chemical bath (CBD-d and SCCBD-d).

Because reproducibility is important in the lab and industry, we produced a large number

of samples per deposition group to understand the number of shunt devices due to poor

coverage of the SnO2, as summarized in Figure S7c. The lowest number of shunts was

found for devices in the ALD control and SC-CBD-d whereas relatively higher

percentage of shunts was found for SC devices and those with CBD-d. These results

stress the importance of using a combination of spin-coating and a dilute chemical bath

for improved reproducibility. We note that the least number of shunts, while maintaining

power conversion efficiencies close to 20%, were obtained with SCCBD-d, and therefore

this is the optimized procedure for reproducibility.

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0.0 0.2 0.4 0.6 0.8 1.0 1.210-6

10-5

10-4

10-3

10-2

10-1

100

101

log

(|I /

mA

|)

Voltage / V

ALD SC SC-CBD CBD-d SCCBD-d

No ESL

28

4234

46

8

ALD SC SC-CBDCBD-d

SCCBD-d0

20

40

60

80

100

shun

ts /

%

ESL type

-0.5 0.0 0.5 1.0 1.5-0.4

-0.2

0.0

0.2

0.4

bare FTO SC SC-CBD CBD-d SCCBD-d

Cur

rent

den

sity

/ m

A c

m-2

Potential / V vs Ag/AgCl (KCl sat'd)

a b

c

Figure S7. Electron blocking properties of SnO2 films deposited by different

methods. a. Cyclic voltammograms of different ESLs deposited on FTO electrode,

measured with a scan rate of 100 mV s-1 in 1 mM K4Fe(CN)6 + 1 mM K3Fe(CN)6 in

aqueous 0.5 M KCl, pH 7 as electrolyte solution, b. dark J-V characteristics and c. shunt

percentage (Devices that showed short-circuited J-V measurements, but had no visible

damage during film deposition) for devices employing bare FTO, atomic layer deposited

(ALD), spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-treatment (SC-

CBD), dilute chemical bath only (CBD-d), spin coated SnO2 and dilute chemical bath

post-treatment (SC-CBD-d), deposited on FTO as ESLs.

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a b

c d

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

25

0 10 20 30 40 50

10

15

20

Cur

rent

den

sity

/ m

A cm

-2

Voltage / V

PC

E %

time / s

19.2%

Maximum power point tracking

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

25

0 10 20 30 40 50

10

15

20

Cur

rent

den

sity

/ m

A cm

-2

Voltage / V

PCE

%

time / s

19%

Maximum power point tracking

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

25

0 10 20 30 40 50

10

15

20

Cur

rent

den

sity

/ m

A cm

-2

Voltage / V

PC

E %

time / s

20.8%

Maximum power point tracking

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

25

0 10 20 30 40 50

10

15

20

Maximum power point tracking

Cur

rent

den

sity

/ m

A cm

-2

Voltage / V

20%

PCE

%

time / s

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

25

0 10 20 30 40 50

10

15

20

Cur

rent

den

sity

/ m

A cm

-2

Voltage / V

PCE

%

time / s

19.5%

Maximum power point tracking

e

Figure S8. Current-voltage and stabilized PCE characteristics of devices. The J-V curves and maximum power point tracking (MPPT, as the inset) of the best performing planar perovskite solar cells based for a. ALD , b. spin coated SnO2 (SC), c. spin coated SnO2 and chemical bath post-treatment (SC-CBD), d. dilute chemical bath only (CBD-d), e. spin coated SnO2 and dilute chemical bath post-treatment (dilute SC-CBD).

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Table. S1 Backward scan (BW) photovoltaic parameters and maximum power point tracking of planar perovskite solar cells. Scan rate of 10 mV/s at room temperature.

ESL typeVOC

[V]

JSC

[mA cm-2]

FF Champion PCE

[%]

Light intensity

[mW cm-2]

MPP[%]

ALD 1.17 21.95 0.72 19.17 97.1 19.01

SC 1.14 21.72 0.76 19.21 97.2 19.5

SC-CBD 1.18 22.37 0.77 20.46 98.4 20.78

CBD-d 1.13 22.70 0.74 19.66 97 19.24SC-CBD-d 1.12 22.12 0.77 19.94 96.3 19.96

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Figure S9. Performance parameters of PSCs. a. Open-circuit voltage b. fill factor, c. short-circuit current and d. power conversion efficiency and e. hysteresis (defined as the difference in efficiency between the backward and forward scan) of several planar perovskite solar cells based on atomic layer deposited (ALD), spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-treatment (SC-CBD), dilute chemical bath only (CBD-d), spin coated SnO2 and dilute chemical bath post-treatment (SC-CBD-d), deposited on FTO as ESLs. All J-V data were recorded with a scan rate of 10 mV/s under simulated one sun illumination (AM 1.5G) at room temperature.

13

Figure S10. Incident photon-to-current efficiencies (IPCE) of solution processed planar perovskite solar cell based on spin coated SnO2 and chemical bath post-treatment (SC-CBD).

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0 10 20 30 40 50 600.0

0.2

0.4

0.6

0.8

1.0 full illuminationroom temperature

Nor

mal

ized

MP

P

time / h

ALD SC

SC-CBD CBD-d

a c b

0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

2510 mV s-1

ALD SC SC-CBD CBD-d

Cur

rent

den

sity

/ m

A cm

-2

Voltage / V0.0 0.2 0.4 0.6 0.8 1.0 1.2

0

5

10

15

20

25

ALD SC SC-CBD CBD-d

10 mV s-110 mV s-1

Cur

rent

den

sity

/ m

A cm

-2

Figure S11. Current-voltage and stability characteristics of planar PSCs. a.

Backward scan J-V characteristics before aging, b. long-term ageing MPPT under

constant full sun illumination, and c. J-V curves after ageing of high performance planar

devices based on ALD, spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-

treatment (SC-CBD), and dilute chemical bath only (CBD-d) ESLs.

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Table S2. Backward photovoltaic characteristics before and after aging (under constant

full sun illumination at room temperature and constant purging of nitrogen gas) of high

performance planar perovskite solar cells with SnO2-based ESLs based on atomic layer

deposition (ALD), spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-

treatment (SC-CBD), dilute chemical bath only (CBD-d), deposited on FTO as ESLs. All

measured at 10 mV s-1 scan rate under full sun illumination at room temperature.

ESL type Measurement state

VOC[V]

JSC[mA cm-2]

FF PCE[%]

Light intensity [mW cm-2]

Before aging 1.13 20.29 0.72 18.34 90.2ALD

After aging 1.14 19.43 0.72 16.35 96.8

Before aging 1.15 21.38 0.75 19.17 96.6SC

After aging 1.16 21.40 0.73 18.42 97.6

Before aging 1.18 22.03 0.76 20.44 97SC-CBD After aging 1.17 22.59 0.75 20.73 96.1

Before aging 1.12 21.67 0.76 18.42 99.8CBD-d

After aging 1.13 22.70 0.74 19.66 97

16

0 20 40 60 80 1000

5

10

15

20

25

ALD SC SC-CBD CBD-d

10 mV s-1

PC

E %

time / days

Figure S12. Dark, shelf stability of PSCs. Power conversion efficiency as a function of time for unencapsulated planar solar cells stored in dry air based on atomic layer deposition (ALD), spin coated SnO2 (SC), spin coated SnO2 and chemical bath post-treatment (SC-CBD), dilute chemical bath only (CBD-d), spin coated SnO2 deposited on FTO as ESLs.

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References

(1) Kavan, L.; Tétreault, N.; Moehl, T.; Grätzel, M. The Journal of Physical Chemistry C 2014, 118, 16408.

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