Supporting information

High performance ambient-air-stable FAPbI3 perovskite solar cells with molecule-passivated Ruddlesden-Popper/3D heterostructured film

Tianqi Niu,‡a Jing Lu,‡a Ming-Chun Tang,b Dounya Barrit,b Detlef-M. Smilgies,c Zhou Yang, a Jianbo Li,a Yuanyuan Fan,a Tao Luo,a Iain McCulloch,b Aram Amassian,*b Shengzhong (Frank) Liu*ad and Kui Zhao*a

a Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education; Shaanxi Key Laboratory for

Advanced Energy Devices; Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials

Science and Engineering, Shaanxi Normal University, Xi’an 710119, China. Email: zhaok@snnu.edu.cnb King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC) and Physical

Science and Engineering Division (PSE), Thuwal 23955-6900, Saudi Arabia.

Email: aram.amassian@kaust.edu.sa c Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 14850, USA.d Dalian National Laboratory for Clean Energy; iChEM, Dalian Institute of Chemical Physics, Chinese Academy

of Sciences, Dalian, 116023, China. Email: szliu@dicp.ac.cn

‡ T.N. and J.L. contributed equally.

Corresponding author: zhaok@snnu.edu.cn; aram.amassian@kaust.edu.sa; szliu@dicp.ac.cn

Electronic Supplementary Material (ESI) for Energy & Environmental Science.This journal is © The Royal Society of Chemistry 2018

Experimental Section

Solution preparation and device fabrication

Materials preparation: Lead iodide (PbI2, 99.9985%) was purchased from AlfaAesar.

Formamidine iodide (FAI), Butylamine iodide (BAI), Butylammonium Bromide

(BABr), Butylammonium Chloride (BACl), Lead(II) bromide (PbBr2, 99.99%) and

Lead(II) chloride (PbCl2, 99.99%) were purchased from p-OLED. N,N-

dimethylformamide (DMF, 99.8%), dimethylsulfoxide (DMSO, 99.9%) and γ-

butyrolactone (GBL, 99%) were purchased from Sigma-Aldrich. ITIC and IDTBR

were purchased from One-material. All chemicals were used as received without

further purification.

Solution preparation: The precursor solution preparation was conducted under inert

atmosphere inside a nitrogen glove box. The FAPbI3 precursor solution (1.2M) was

prepared with equimolar PbI2 and Formamidine iodide (FAI) dissolved in a mixture of

dimethylsulfoxide (DMSO), γ-butyrolactone (GBL) and N,N-dimethylformamide

(DMF) (volume ratio of 7:7:6) in a glovebox. To form a quasi-2D perovskite solution

(1.2M), BAX, FAI, PbX2 and PbI2 (X denotes halogen) were mixed with the ratio of

2:60:1:60 and dissolved in the same solvent recipe as FAPbI3. All solutions were

filtered prior to solution-casting. ITIC and IDTBR solutions were resolved in

chlorobenzene with the concentration of 0.4 mg/ml. The Spiro-OMeTAD solution

was prepared by dissolving 90 mg Spiro-OMeTAD, 22 μL lithium

bis(trifluoromethanesulfonyl) imide in acetonitrile and 36 μL 4-tert-butylpyridine in 1

mL chlorobenzene.

Device fabrication: The FTO-coated glass (2.5 cm * 2.5 cm) was cleaned by

sequential sonication in acetone, isopropanol and ethanol for 30 min each and then

dried under N2 flow and treated by O3 plasma for 15 min. The TiO2 was prepared by

chemical bath deposition with the clean substrate immersed in a TiCl4 (CP,

Sinopharm Chemical Reagent Co., Ltd) aqueous solution with the volume ratio of

TiCl4 : H2O equal to 0.0225 : 1 at 70 °C for 1 hour. The spin-coating was

accomplished under inert atmosphere inside a nitrogen glove box. The procedure was

performed at 1000 r.p.m. for 10 s followed by 4000 r.p.m. for 40 s. At ca. 25 s before

the end of the last spin-coating step, 100 μL of chlorobenzene solvent or loaded

solution was dropped onto the substrate. The substrates were then placed onto a

hotplate for 30 min at 150 °C. Subsequently, the HTM were deposited on top of the

perovskite by spin coating at 5000 r.p.m. for 30 s followed by evaporation of 100 nm

gold electrode on the top of the cell.

Characterization

Optical metrology: UV-Visible absorption spectra were acquired on a PerkinElmer

UV-Lambda 950 instrument. Steady-state Photoluminescence (PL) (excitation at 510

nm) was measured with an Edinburgh Instruments Ltd (FLS980 spectrometer).

Electronic microscopy: The surface morphology and structure of the perovskite films

were characterized by SEM (FE-SEM; SU-8020, Hitachi) and Atomic force

microscopy (AFM, Dimension ICON), respectively.

X-ray diffraction (XRD) measurements were carried out in a θ-2θ configuration with

a scanning interval of 2θ between 5 and 60 on a Rigaku Smart Lab (X-ray Source:

Cu Kα; = 1.54 Å).

Grazing incidence wide angle X-ray scattering (GIWAXS) measurements were

performed at D-line at the Cornell High Energy Synchrotron Source (CHESS). The

wavelength of the X-rays was 0.972 Å with a bandwidth ∆λ/λ of 1.5%. The scattering

signal was collected by a Pilatus 200K detector, with a pixel size of 172 µm by 172

µm placed 184.0066 mm away from the sample position. The incident angle of the X-

ray beam was 0.35 degree. Spin-coating experiments were conducted at a custom-

built spin-coating stage with splashing of solvent protected using kapton tape and

controlled from a computer outside the hutch. The exposure time was kept at 0.5 s to

obtain the detailed information of the process.

UPS measurements: Ultraviolet photoelectron spectroscopy (UPS) was measured

with a monochromatic He I light source (21.22 eV) and a VG Scienta R4000 analyzer.

Solar cell characterizations: The J-V performance of the perovskite solar cells was

measured using a Keithley 2400 source-meter under ambient condition at room

temperature, and the illumination intensity was 100 mW cm-2 (AM 1.5G Oriel solar

simulator). The scan rate was 0.3 V s-1. The delay time was 10 ms; and the scan step

was 0.02 V. The power output of the lamp was calibrated by a NREL-traceable KG5-

filtered silicon reference cell. The device area of 0.09 cm2 was defined by a metal

aperture to avoid light scattering from the metal electrode onto the device during the

measurement. The EQE was characterized on a QTest Station 2000ADI system

(Crowntech. Inc., USA), and the light source was a 300 W xenon lamp. The

monochromatic light intensity for EQE measurements was calibrated with a reference

silicon photodiode.

Mobility measurement: Electron-only devices (FTO/c-TiO2/perovskites/PCBM/Ag)

were fabricated to measure the electron mobility of the devices. The dark J-V

characteristics of the electron-only devices were measured by a Keithley 2400

sourcemeter. The mobility was extracted by fitting the J-V curves with the Mott-

Gurney equation. The trap state density was determined by the trap-filled limit

voltage using equation 2.

Electrical impedance spectroscopy (EIS) measurement: Electrical impedance

spectroscopy (EIS) measurements were conducted using an electrochemical

workstation (IM6ex, Zahner, Germany) with the frequency range from 10 Hz to 4

MHz at open-circuit voltage in the dark.

Contact angle measurements were conducted on a Dataphysics OCA-20 with a drop

of ultrapure water (0.05 mL). The photographs were taken 1 second after water

dripping.

(FAPbI3)n(BA2PbX4) (FAPbI3)n(BA2PbX4)

Dripping ITIC or IDTBR loaded solution

NCCN

S

S

S

S

C6H13 C6H13

C6H13 C6H13

O

O

CN

NC

ITIC

S

SNS N

SN

O

S

NSN

SN

O

S

IDTBR

(a)

(b)

Fig. S1. (a) Molecular structure of the selected semiconducting molecules with Lewis base functional groups. (b) Schematic diagram of loaded anti-solvent dripping strategy for fabricating RP/3D heterostructured perovskite films.

Fig. S2. (a) Cross-sectional scanning electron microscopy (SEM) image of the control FA film. (b) Atomic force microscopy (AFM) images of the control FA and IDTBR-FABABr films with root-mean-squared (RMS) roughness.

300 400 500 600 700 8000

20

40

60

80

100

Wavelength (nm)

Control FA IDTBR- FABABr 0

4

8

12

16

20

24

Integrated Jsc (m

A cm-2)

EQE

(%)

Fig. S3. External quantum efficiency (EQE) and the corresponding integrated current density for the champion control FA and IDTBR-FABABr devices.

n=10

500 nm

n=40

500 nm

(a) (b)

0.0 0.4 0.8 1.2-25

-20

-15

-10

-5

0

Bias (V)

Curre

nt d

ensit

y (m

A cm

-2)

n=10 n=40 n=60

(c) (d)

500 nm

n=60

Fig. S4. (a-c) Plan-view SEM images for (FAPbI3)n(BAPbI4) RP/3D heterostructured perovskite films with n= 10, 40 and 60. (d) J-V curves of champion perovskite devices with different n values.

-25 -20 -15 -10 -5 0

5

10

15

20

25

q z (n

m-1)

qxy (nm-1)-25 -20 -15 -10 -5 0

5

10

15

20

25

q z (n

m-1)

qxy (nm-1)

-25 -20 -15 -10 -5 0

5

10

15

20

25

q z (n

m-1)

qxy (nm-1)

FABACl

FABAI

FABABr

-25 -20 -15 -10 -5 0

5

10

15

20

25q z

(nm

-1)

qxy (nm-1)

Control FA(a) (b)

(c) (d)

Fig. S5. In situ GIWAXS measurements performed at the end of spin coating for the control FA and RP/3D heterostructured films showing differences in the shape and intensity of scattering patterns.

500 nm

RMS=15.6 nm RMS=20.7 nm

RMS=20.7 nmRMS=24.0nm RMS=21.2 nm

500 nm 500 nm 500 nm

500 nm

FABACl

FABAI FABABr FABACl

(a) (b)

(c)

500 nm

FABABr

Fig. S6. (a-b) Plan-view SEM images of FABABr and FABACl films. (c) AFM images of the RP/3D heterostructured perovskite films with root-mean-squared (RMS) roughness.

FABAI FABACl

-25 -20 -15 -10 -5 0

5

10

15

20

q z (n

m-1)

qxy (nm-1)

Control FA

-25 -20 -15 -10 -5 0

5

10

15

20

q z (n

m-1)

qxy (nm-1)-25 -20 -15 -10 -5 0

5

10

15

20

q z (n

m-1)

qxy (nm-1)

(a) (b) (c)

Fig. S7. Ex situ GIWAXS patterns of the control FA, FABAI and FABACl films.

1.5 1.6 1.7

hv (eV)

FABABr

1.54

1.5 1.6 1.70.00

0.02

0.04

0.06

0.08

0.10

hv (eV)

(F(R

)hv)

2

1.53

Control FA

1.5 1.6 1.7

hv (eV)

FABACl

1.55

1.5 1.6 1.7

1.53

FABAI

hv (eV)

Fig. S8. Tauc plots of control FA and RP/3D heterostructured films, showing determination of the estimated bandgaps from the intercepts, derived from the UV-Vis spectra.

750 800 8500

1 Control FA FABAI FABABr FABACl

Wavelength (nm)

Norm

alize

d in

tens

ity (a

.u.)

Fig. S9. Normalized steady-state photoluminescence (PL) spectra for the four films.

0.01 0.1 11E-6

1E-5

1E-4

1E-3

0.01

0.1

1

Voltage (V)

FABABr

electron=3.56 cm2V-1S-1ntrap=1.18*1016 cm-3

VTFL=0.21V

Curre

nt (A

)

0.01 0.1 1

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

electron=4.23 cm2V-1S-1ntrap=8.44*1015 cm-3

VTFL=0.15V

Voltage (V)

Curre

nt (A

) Control FA

0.01 0.1 1

1E-3

0.01

0.1

1

electron=3.76 cm2V-1S-1

Curre

nt (A

)

Voltage (V)

ntrap=6.18*1015 cm-3

VTFL=0.11V

FABAI

0.01 0.1 1

1E-4

1E-3

0.01

0.1

electron=1.88 cm2V-1S-1

ntrap=1.41*1016 cm-3Curre

nt (A

)

Voltage (V)

FABACl

VTFL=0.25V

Fig. S10. Dark I-V measurement data of the electron-only devices with the architecture FTO/TiO2/perovskite/PCBM/Ag for the four cases displaying VTFL kink point behavior.

300 400 500 600 700 8000

20

40

60

80

100

FABAI FABABr FABACl

0

4

8

12

16

20

24

Wavelength (nm)

EQE

(%)

Integrated Jsc (m

A cm-2)

0.0 0.4 0.8 1.2-25

-20

-15

-10

-5

0

Bias (V)

Curre

nt d

ensit

y (m

A cm

-2)

FABAI FABABr FABACl

(a) (b)

Fig. S11. (a) J-V curves for champion devices based on RP/3D heterostructured films. (b) EQE and the corresponding integrated current density for the three cases.

0 100 200 3000

5

10

15

20

25

Curre

nt d

ensit

y (m

A cm

-2)

PCE (%)

Time (sec)

FABACl

0

5

10

15

20

25

Jsc=20.26 mA/cm2

Vmax=0.86VPCE=17.42 %

0 100 200 3000

5

10

15

20

25

Time (sec)

PCE (%)

Curre

nt d

ensit

y (m

A cm

-2)

FABAI

Vmax=0.86V

0

5

10

15

20

25

PCE=18.73 %

Jsc=21.78 mA/cm2

0 100 200 3000

5

10

15

20

25

Time (sec)

Curre

nt d

ensit

y (m

A cm

-2)

Vmax=0.86V

FABABr

0

5

10

15

20

25

PCE (%)

PCE=18.69 %

Jsc=21.73 mA/cm2

Fig. S12. The stabilized power output of the champion devices based on the RP/3D heterostructured films measured at a fixed maximum power point (MPP) voltage as a function of time.

0.0 0.4 0.8 1.2-25

-20

-15

-10

-5

0

Curre

nt d

ensit

y (m

A cm

-2)

Bias (V)

FABACl Reverse

17.66% PCE Forward

15.95% PCE

0.0 0.4 0.8 1.2-25

-20

-15

-10

-5

0

Bias (V)

Curre

nt d

ensit

y (m

A cm

-2) FABAI

Reverse 18.82% PCE

Forward 18.03% PCE

0.0 0.4 0.8 1.2-25

-20

-15

-10

-5

0

Bias (V)

Curre

nt d

ensit

y (m

A cm

-2) FABABr

Reverse 18.76% PCE

Forward 17.95% PCE

Fig. S13. J-V curves recorded in both the reverse and forward scan directions for the RP/3D devices.

Fig. S14. (a) UPS spectrum in the high binding-energy region of post-annealed FABABr film to determine the Ecutoff level. Inset: linear extrapolation in the low-binding-energy region for the value of Ev-Ef, the Fermi energy (abbreviated as Ef) and the valence band energy (Ev). (b) Energy band diagram of FABABr film calculated from the Tauc plot (Fig. S8) and UPS results. (c) The corresponding energy diagrams in the completed device.1, 2

500 nm

ITIC-FABABr

500 nm

RMS=21.2 nm

ITIC-FABABr

(a) (b)

Fig. S15. (a) Plan-view SEM image of ITIC-FABABr films. (b) AFM image of ITIC-FABABr film with root-mean-squared (RMS) roughness.

500 600 700 800 9000

1

2

3 FABABr ITIC-FABABr IDTBR-FABABr

Wavelength (nm)

Abso

rban

ce (a

.u.)

Fig. S16. UV spectroscopy measurement for FABABr films with and without ITIC or IDTBR passivation layer on glass.

0 10 20 30 400

20

40

Z (o

hm)

Z (ohm)

FABABr ITIC-FABABr IDTBR-FABABr Fitting linear

Rs Rco

Cco Crec

Rrec

(a) (b)

Fig. S17. (a) The equivalent circuit composed of the series resistance (Rs), contact resistance (Rco) and recombination resistance (Rrec). (b) Nyquist plot of EIS in the high-frequency regime for the FABABr and passivated devices.

0.01 0.1 11E-5

1E-4

1E-3

0.01

0.1

VTFL=0.09V

electron=4.89 cm2V-1S-1ntrap=5.06*1015 cm-3

Voltage (V)

Curre

nt (A

)

ITIC-FABABr

0.01 0.1 11E-4

1E-3

0.01

0.1

Voltage (V)

Curre

nt (A

)

IDTBR-FABABr

electron=5.79 cm2V-1S-1ntrap=3.93*1015 cm-3

VTFL=0.07V

Fig. S18. Dark I-V measurement of the electron-only devices for the ITIC-FABABr and IDTBR-FABABr cases displaying VTFL kink point behavior.

0 100 200 3000

5

10

15

20

25

Time (sec)

PCE (%)

Curre

nt d

ensit

y (m

A cm

-2)

ITIC-FABABr

Vmax=0.90V

0

5

10

15

20

25

PCE=20.01 %

Jsc=22.23 mA/cm2

0.0 0.4 0.8 1.2-25

-20

-15

-10

-5

0

Bias (V)

Curre

nt d

ensit

y (m

A cm

-2)

ITIC-FABABr Reverse

20.10% PCE Forward

19.19% PCE

(a) (b) (c)

300 400 500 600 700 8000

20

40

60

80

100

Wavelength (nm)

EQE

(%)

ITIC-FABABr

0

4

8

12

16

20

24Integrated J

sc (mA cm

-2)

Fig. S19. Characteristics of devices based on ITIC-FABABr film. (a) J-V curves recorded in both the reverse and forward scan directions. (b) The stabilized power output and (c) EQE of the champion device.

0 10 20 30 40 50 600.00.20.40.60.81.0

Time (days)

Norm

alize

d PC

E

Control FA FABAI FABABr FABACl

10 20 30 40 50 60 70 80

Inte

nsity

(a.u

.)

2degrees)

FABACl

FABABr

FABAI*Control FA

FABAIControl FA FABAClFABABr

10 days

60 days

FABAI

81.9°

Control FA

70.7° 83.1°

FABACl

82.8°

FABABr

(a)

(c)

(b)

(d)

Fig. S20. Long term environmental stability characterization. (a) Pictures of the control FA and RP/3D heterostructured perovskite films before and after aging under ambient conditions with 30-40% relative humidity at room temperature. (b) XRD patterns of the four cases before and after aging under ambient conditions with 30-40% relative humidity at room temperature. (c) Contact angle of water on different perovskite films showing increased hydrophobicity of the RP/3D films compared with the control film. (d) Long-term stability measurements of both solar cells without any encapsulation under ambient conditions with 30-40% relative humidity. After 60 d, the RP/3D FABAI, FABABr and FABACl fabricated devices exhibit significantly improved stability against humidity, maintaining 56.1%, 74.2% and 69.4% of their initial PCEs, respectively, in contrast to the control device at only 20.2% of initial PCE.

88.7°

IDTBR-FABABr

92.5°

ITIC-FABABr

0 10 20 30 40 50 60

0.6

0.8

1.0

Time (days)

Norm

alize

d PC

E

FABABr ITIC-FABABr IDTBR-FABABr

(a)

(b)

Fig. S21. (a) Contract angle of water on ITIC-FABABr and IDTBR-FABABr films. (b) Long-term stability measurements for the FABABr and passivated devices. For the ITIC passivated device, 90.1% of the initial PCE value was retained after 60 days, which is better than the value of FABABr at 74.2% and IDTBR passivated one at 87.3%.

0 20 40 60 80 100 120 1400.0

0.2

0.4

0.6

0.8

1.0

Time (h)

Norm

alize

d PC

E (%

)

Control FA FABABr ITIC-FABABr IDTBR-FABABr

Fig. S22. Operational Stability. The evolution of the PCEs for the non-encapsulated control FA，FABABr，ITIC-FABABr and IDTBR-FABABr devices exposed to continuous illumination (100 mW cm-2) under open-circuit condition in air (50-60% RH and 50 ºC). The ITIC-FABABr and IDTBR-FABABr based devices still maintained 72.6% and 68.9% of the initial values after 130h continuous illumination, respectively, which significantly outperform the control one.

Table S1. Photovoltaic parameters of devices based on the control FA and IDTBR-FABABr films.

VOC

(V)

JSC

(mA cm-2)FF(%)

PCE (%)

PCEmax

(%)

Control FA 1.05±0.01 24.1±0.6 74.0±1.9 18.6±0.5 19.15

IDTBR-FABABr 1.07±0.01 24.1±0.5 76.1±1.5 19.5±0.5 20.62

Table S2. The hysteresis parameters of champion devices based on the control FA and IDTBR-FABABr films.

Scanningmode

VOC

(V)

JSC

(mA cm-2)FF(%)

PCE(%)

HysteresisIndex (%)

Reverse 1.06 24.09 74.8 19.15Control FA

Forward 1.05 22.44 72.7 17.1110.7

Reverse 1.10 24.40 76.9 20.62IDTBR-FABABr

Forward 1.09 23.89 76.7 19.913.4

Table S3. Photovoltaic parameters of champion devices based on the (FAPbI3)n(BAPbI4) films with different n values.

(FAPbI3)n(BAPbI4)V

OC

(V)

JSC

(mA cm-2)FF(%)

PCE(%)

RS

(Ω cm-2)

RSh

(Ω cm-2)

n=10 1.04 21.46 66.2 14.79 97.7 12246

n=40 1.03 22.80 71.4 16.75 73.7 25655

n=60 1.06 23.92 74.0 18.84 69.5 50082

Table S4. Photovoltaic parameters of devices based on the RP/3D heterostructured films.

VOC

(V)

JSC

(mA cm-2)FF(%)

PCE(%)

PCEmax

(%)FABAI 1.05±0.02 23.8±0.3 72.7±2.1 18.2±0.4 18.84

FABABr 1.06±0.02 23.7±0.4 73.1±1.3 18.1±0.4 18.76FABACl 1.06±0.01 22.9±0.2 70.3±1.4 17.1±0.5 17.66

Table S5. The hysteresis parameters of champion devices based on the RP/3D heterostructured films.

Scanningmode

VOC

(V)

JSC

(mA cm-2)FF(%)

PCE(%)

Hysteresisindex (%)

Reverse 1.06 23.92 74.0 18.84FABAI

Forward 1.05 23.76 72.3 18.034.3

Reverse 1.08 23.77 72.9 18.76FABABr

Forward 1.07 23.40 71.2 17.765.3

Reverse 1.08 23.02 71.0 17.66FABACl

Forward 1.01 22.64 69.5 15.959.7

Table S6. Summaries of EIS parameters for different devices.R

s

(Ω）

Rco

(Ω）

Rrec

(Ω）

Cco

(F cm-2)

Crec

(F cm-2)FABABr 13.7 39.4 349.6 2.4×10-9 9.8×10-8

ITIC-FABABr 8.4 32.5 373.9 7.8×10-9 9.6×10-8

IDTBR-FABABr 9.5 29.5 473.1 6.2×10-8 9.1×10-9

Table S7. Photovoltaic parameters of devices based on the ITIC-FABABr film.V

OC

(V)

JSC

(mA cm-2)FF(%)

PCE(%)

PCEmax

(%)ITIC-FABABr 1.07±0.01 24.0±0.5 75.0±1.3 19.2±0.4 20.10

Table S8. The hysteresis parameters of champion devices based on the ITIC-FABABr films.

Scanningmode

VOC

(V)

JSC

(mA cm-2)FF(%)

PCE(%)

HysteresisIndex (%)

Reverse 1.07 23.86 78.6 20.10ITIC-FABABr

Forward 1.06 23.48 76.7 19.194.1

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