Supplementary Information for

Quantification of light-enhanced ionic transport in

lead iodide perovskite thin films and its solar cell

applications

Yi-Cheng Zhao1, Wen-Ke Zhou1, Xu Zhou1, Kai-Hui Liu1,2*, Da-Peng Yu1,2, Qing

Zhao1,2*

1State Key Laboratory for Mesoscopic Physics and Electron Microscopy Laboratory,

School of Physics, Peking University, Beijing 100871, China.

2Collaborative Innovation Center of Quantum Matter, Beijing 100084, China.

*Correspondence to: khliu@pku.edu.cn; zhaoqing@pku.edu.cn

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5 mW cm-2

dark

t = 0 mina

b

c

20 mW cm-2

t = 2 min t = 4 min

Figure S1．Optical dynamic images of perovskite film under electric poling and

varied illumination intensity, in 10 Torr vacuum at room temperature. (a) The

film shows little change under dark at 100 V bias for 4 minutes (2 V m-1 high-field

poling). (b) The film shows black threads at the cathode, and moves toward anode in

4 minutes poling, under 5 mW cm-2 illumination with the same electric field.

Prolonged electrical poling for another 4 minutes under 5 mW cm -2 light intensity

cannot induce any further change. (c) Following the total 8 minutes’ poling under 5

mW cm-2, the film presents further destructed morphology near cathode after the 4

minutes poling under 20 mW cm-2 illumination. (Ionic motion almost stops after 4

minutes poling under 5 mW cm-2, but ions can move again to further change the

optical images with many black dots formed at the cathode under stronger

illumination. Note the gap size between the two gold electrodes is 50 m.)

2

10 15 20 25 30

0.0

0.5

1.0

1.5

2.0

In

tens

ity (N

orm

.)

2 theta (degrees)

#

Initial

After poling

(110) (220) Au Au

Si

Pb

IPb/I

Au Au Au

a b

c d

Initial

After poling After poling zoom-in

700 600 500 400 300 200 100 0

0.0

0.5

1.0

1.5

2.0

2.5Poling A

u

Initial

Si 2

p

Inte

nsity

(Nor

m.)

Binding energy (eV)

I 3d

O 1

s

Pb

4d

C 1

s

I 4s P

b 4f

I 4p

I 4d

Pb

5d

636 630 624 618 144 138 132

0.0

0.5

1.0

1.5

2.0

Inte

nsity

(Nor

m.)

Binding energy (eV)

I3d

Pb4f

e f

Figure S2. (a) X-ray diffraction patterns for Au/MAPbI3/Au lateral device on silica

substrate before and after high-field poling experiment, corresponding to the device in

Figure 1. ‘*’ denotes the poling-induced new phase PbI2 in the device, and ‘#’ denotes

the signals from silica substrate. The (110) (220) intensity from perovskite film

significantly decreased after electric poling, indicating the destructed perovskite

material in the device. (b) Distribution of Si, Pb, I and the corresponding Pb/I ratio for

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the lateral Au/perovskite/Au structure without high-field poling on silica substrate,

through energy dispersive spectra. The gray arrow indicates the scan direction from

negative to the positive electrode. (c) Distribution of Si, Pb, I and the corresponding

Pb/I ratio for lateral structure after high-field poling in air under 1 V um-1 electric field

for 30 s. The scan area includes the dendrite structure. In that area, a signal of Pb and I

present sharp increase when a signal of silicon from the substrate shows a fast

decrease. (d) Zoom-in for the area includes dendrite structure. (e) X-ray photoelectron

spectra for perovskite with and without high-field poling. The global spectra for

destructed film present significant signal of Si(2p) and O(1s) from the substrate

below, indicating the formation of voids in the film with poling. (f) A closer look at Pb

4f and I 3d core levels show symmetric peaks. For I 3d, there is little shift in the

spectra. However, for Pb 4f, the orange line presents a larger full width at half

maximum (FWHM) compared to gray line without poling, which may be correlated

with the PbI2 formation in the poled sample, although both of them show a same

binding energy. It is hard to confirm whether reduction of Pb2+ occurs or not, because

both of them presents metallic Pb1.

4

5

3.5 4.0 4.5 5.0 5.5 6.0 6.5

0.0

0.2

0.4

0.6

0.8

1.0C

ount

s (N

orm

.)

Binding energy (eV)

PbAc2

0 200 400 600 800 1000

1

10

100

PL

inte

nsity

(a.u

.)

Time (ns)

=267.9 ns

a b

-1.0 -0.5 0.0 0.5 1.0-8

-4

0

4

8

Cur

rent

(mA

)

Bias voltage (V)

c

Figure S3. (a) Photoelectron energy spectroscopy (3.4-6.2 eV) for the prepared

MAPbI3 on TiO2/FTO substrate based on PbAc2/MAI precursor solution. It is

measured using a Photoelectron Spectrometer (Riken Keiki AC-2). The signal from

the conduction band is almost zero, implying that the Fermi level of our sample is

located around the valence band. (b) Time-resolved photoluminescence spectra for

MAPbI3 film on silica substrate prepared from PbAc2/MAI precursor solution. (c) The

current-voltage curves for ITO/PEDOT:PSS/Perovskite/Au structure, with an non-

rectifying behavior over the range of 2 V with a large current value, which indicates

the p type character of our sample.

6

15 20 25 30 35-1

0

1

2

3

4

5

(211)

120 K

150 K

190 K

215 K

(220)Inte

nsity

(Nor

m.)

2 theta (degree)

(202) (213)(110)

245 K

150 200 250 300 3500.00

0.03

0.06

0.09

0.12

0.15

Rel

ativ

e in

tens

ity (%

)

Temperature (K)

(211) facet (202) facet

Ttrans=190 K

a b

Figure S4 (a) X-ray diffraction patterns for MAPbI3 under different temperatures

from 120 to 245 K. (b) The relative intensity of the peak values for (211), (202) facets

as a function of temperature. The phase transition from orthorhombic to tetragonal

can be indicated by the abnormal increase for the intensities of (211), (202) facets

around 190 K.

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a b

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0

Cou

nts

Sputtering time (s)

Pb/I Pb I

0 20 40 60 80 1000.0

0.5

1.0

1.5

2.0C

ount

s

Sputtering time (s)

Pb/I Pb I

Figure S5. (a) Ionic counts versus sputtering time for Pb+, I+, and the ratio Pb/I is

presented for the film without residual PbI2 and (b) with residual PbI2. The gray area

marks the bottom of the film with sharp drop of the counts at ~50 s. Although Pb/I

ratio increases in both cases due to different adhesive property to the substrate, the

film with PbI2 shows a larger value than that without PbI2. Since Pb/I ratio in PbI2 is

0.5 that is larger than in MAPbI3, we attribute the greater increase of Pb/I ratio in b, to

the residual PbI2 at the bottom of perovskite film.

Web Enhanced Objects. Supplementary Movie 1-3. Real time optical image recording

of the lateral structure Au/MAPbI3/Au under 2V m-1 electric poling under 0 mW cm-2

(Movie 1), 5 mW cm-2 (Movie 2), 20 mW cm-2 (Movie 3).

1 Lindblad R, Bi D, Park BW, Oscarsson J, Gorgoi M, Siegbahn H, et al. Electronic Structure of TiO2/CH3NH3PbI3 Perovskite Solar Cell Interfaces. J Phys Chem Lett. 2014;5:648-53.

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