www.sciencemag.org/cgi/content/full/science.aao5561/DC1

Supplementary Materials for

A generic interface to reduce the efficiency-stability-cost gap of

perovskite solar cells

Yi Hou,* Xiaoyan Du, Simon Scheiner, David P. McMeekin, Zhiping Wang, Ning Li,

Manuela S. Killian, Haiwei Chen, Moses Richter, Ievgen Levchuk, Nadine Schrenker,

Erdmann Spiecker, Tobias Stubhan, Norman A. Luechinger, Andreas Hirsch, Patrik

Schmuki, Hans-Peter Steinrück, Rainer H. Fink, Marcus Halik, Henry J. Snaith,

Christoph J. Brabec*

*Corresponding author. Email: yi.hou@fau.de (Y.H.); christoph.brabec@fau.de (C.J.B)

Published 9 November 2017 on Science First Release

DOI: 10.1126/science.aao5561

This PDF file includes:

Materials and Methods

Figs. S1 to S13

Tables S1 to S4

Materials and Methods

Materials and Preparation

Unless stated otherwise, all materials were purchased from Sigma Aldrich or Merck and used as

received. MAI, FAI, PbBr2, and PbI2, was purchased from Lumtec and Dyesol. To form a 1.4 M

MAPbI3 precursor solution, PbI2 and MAI were mixed with a mole ratio of 1:1 in a mixture of

DMF and DMSO (4:1 v/v). A 1.4 M FA0.83MA0.17Pb1.1Br0.50I2.80 precursor solution was similarly

prepared using a mixture of DMF and DMSO (4:1 v/v). The dry WOx and Ta-WOx nano powders

were prepared via flame spray synthesis using a precursor solution of tungsten and tantalum salts

in organic solvents. The precursor then was fed to a spray nozzle, dispersed by oxygen and ignited

by a premixed methane-oxygen flame. The off-gas was filtered through a steel mesh filter (20

micron mesh size) by a vacuum pump. The WOx and Ta-WOx nano powder obtained was collected

from the filter mesh. A stable suspension was prepared by dispersing the nano powder in ethanol

or isopropanol respectively using an undisclosed dispersant (proprietary information of Avantama

Ltd.). The P3HT, PTB7, pDPP5T-2, PffBT4T-2OD, PDBT-T1 and PDCBT were dissolved in

chlorobenzene or chloroform at concentrations of 5 mg/mL, and followed by stirring on a 60 °C

hot plate for 2 hours.

Solar cell fabrication

First, the patterned ITO substrates were ultrasonically cleaned using acetone and isopropanol for

10 minutes each. On each cleaned ITO substrate, a dense and smooth layer of C60-SAM was

deposited by dipping the ITO substrate into the C60-SAM solution for 24 hours. The SnOx layer

was prepared by spinning SnCl4.5H2O precursor in IPA (17.5mg/mL) at 3000 r.p.m. for 30s and

annealed the film at 140 °C for 45 min. 10 mg/mL PCBM solution in CB was deposited on to the

SnOx at a speed of 4000 r.p.m for 20 s. The as-prepared perovskite precursor solution was filtered

using a 0.45 µm PTFE syringe filter and coated onto substrates at a speed of 4000 r.p.m for 20 s.

The substrate (around 2.5 cm×2.5 cm) was quenched by CB solvent and annealed on a hot plate at

100 ◦C for 10 min in N2. The prepared polymer HTMs were spin-coated at 1000 r.p.m for 35 s.

Subsequently, Ta-WOx and WOx were coated onto polymer HTMs at a speed of 2000 r.p.m for 30

s. Finally, a 100-nm-thick Au counter electrode was deposited onto a hole-transporting layer

through a shadow mask by thermal evaporation.

Device characterizations

j-V characteristics of all the devices were measured using a source measurement unit from BoTest.

Illumination was provided by a Newport Sol1A solar simulator with AM 1.5G spectrum and light

intensity of 100 mWcm-2, which was determined by a calibrated crystalline Si-cell. During device

characterization, a shadow mask with an opening of 10 mm2 was used. For stability test, the

illumination was provided by a white LED (XLamp CXA2011 1300K CCT) and its intensity was

adjusted in a way that the generated photocurrent matched the one under a solar simulator. The

moisture and O2 concentrations were kept below 0.5 p.p.m. for the ageing experiments in N2

atmosphere at room temperature.

Material characterization

External quantum efficiency (EQE) spectra were recorded using an Enli Technology (Taiwan)

EQE measurement system (QE-R), and the light intensity at each wavelength was calibrated using

a standard single-crystal Si photovoltaic cell.

X-ray photoelectron spectroscopy (XPS) measurements were conducted in an ultrahigh vacuum

(UHV) chamber with a base pressure below 5×10−10 mbar using a Scienta ESCA 200 spectrometer

with a monochromatic Al Kα X-ray source (1486.6 eV) and a hemispherical electron energy

analyzer.

Ultraviolet photoelectron spectroscopy (UPS) measurements were performed in the same chamber

with a He I UV source, applying a – 5.00 V bias to the sample. The work function is calculated as

the energetic difference between the Fermi level and the vacuum level, as defined by the

secondary-electron edge. The ionization energy is estimated as the onset of the density of states at

the top of the valence band. Reported results were repeated on at least three spots per sample.

Scanning electron microscopy (SEM): A FEI Helios Nanolab 660 was used to acquire scanning

electron microscopy (SEM) images and to prepare FIB cross-sections. The final polishing with the

ion beam was performed at 30 kV and 80 pA. The SEM micrographs of the cross-sections as well

as the plan view samples were recorded at an acceleration voltage of 2 kV with a current of 100

pA.

X-ray powder diffraction (XRD): X-ray diffraction analysis was performed by classical ex situ

Bragg – Brentano geometry using a Panalytical X'pert powder diffractometer with filtered Cu-Kα

radiation and an X'Celerator solid-state stripe detector.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed on a ToF-SIMS 5

spectrometer (ION-TOF; Munster, Germany) using 25 keV Bi+ bunched down to <0.8 ns. The

primary ion dose density for spectra acquisition was 5 × 1011 ions cm-2 with an area of 100 µm ×

100 µm using negative polarity. Spectra were normalized to their total intensity and calibrated on

C−, O−, C2−, C2H

−, and C3−. Depth profiles were carried out with a crater size of 250 µm × 250 µm

and a measured spot of 50 µm × 50 µm in the center of crater. The sputter beam used was Cs 500

eV and the measurement beam was Bi+ using negative polarity. The interlaced mode was used

with 5s of sputtering and 1s flooding with low energy electrons for charge neutralization. Reported

results were repeated on at least three spots per sample.

Fig. S1. Schematic of the device and the processing temperatures of each layer.

Table S1. The comparison between the light j-V characteristic of the perovskite solar cells with

different hole extraction interfaces under AM 1.5G illumination.

Device

Configuration

Voc

[V]

Jsc

[mAcm-2]

FF

[%]

PCE

[%]

ITO/SAMs/MAPbI3/PDCBT/Au 0.95 20.3 37 7.2

ITO/SAMs/MAPbI3/PDCBT/MoOx/Au 1.00 20.8 60 12.5

ITO/SAMs/MAPbI3/PDCBT/WOx/Au 1.05 21.3 60 13.3

ITO/SAMs/MAPbI3/PDCBT/Ta-WOx/Au 1.06 21.4 75 16.8

ITO glass

Perovskite

HTLs

Au

Ta-WOx

60 °C

100 °C

60 °C

60 °C

Perovskite

HTLs

Au

Ta-WOx

100 °C

100 °C

60 °C

60 °C

ITO glass

140 °C

60 °C

a b

Table S2. The j-V characteristic of the perovskite solar cells with different HTMs under AM

1.5G illumination.

Device

Configuration

Voc

[V]

Jsc

[mAcm-

2]

FF

[%]

PCE

[%]

ITO/C60-SAM/SnOx/PC60BM/FAMA

based perovskite/P3HT/Ta-WOx/Au

1.00 21.2 69 14.5

ITO/C60-SAM/SnOx/PC60BM/FAMA

based perovskite/PTB7/Ta-WOx/Au

1.13 22.6 71 18.5

ITO/C60-SAM/SnOx/PC60BM/FAMA

based perovskite/pDPP5T-2/Ta-WOx/Au

1.15 21.5 76 18.9

ITO/C60-SAM/SnOx/PC60BM/FAMA

based perovskite/PffBT4T-2OD/Ta-WOx/Au

1.16 22.5 68 17.6

ITO/C60-SAM/SnOx/PC60BM/FAMA

based perovskite/PDBT-T1/Ta-WOx/Au

1.17 22.2 77 19.8

ITO/C60-SAM/SnOx/PC60BM/FAMA

based perovskite/PDCBT/Ta-WOx/Au

1.17 22.7 80 21.2

ITO/SAMs/MA based perovskite/doped

spiro-MeOTAD/MoOx/Au

1.05 20.9 59 13.0

ITO/SAMs/ MA based perovskite/undoped

spiro-MeOTAD/Ta-WOx/Au

0.95 20.9 65 12.9

Table S3. Summary of perovskite solar cells employing no additional dopants in HTMs.

Device

Configuration

PCE

[%]

TiO2/Perovskite/CuI1 6.0

TiO2/Perovskite/P3HT2 10.4

TiO2/Perovskite/PBDTTT-C3 9.9

TiO2/Perovskite /CuSCN4 12.4

TiO2/Perovskite /spiro-cyclopentadithiophene5 13.4

TiO2/Perovskite /FK2096 12.7

TiO2/Perovskite / TIPS-pentacene7 11.8

C60/Perovskite /CuPc8 14.5

TiO2/Perovskite /DOR3T-TBDT9 14.9

TiO2/Perovskite /S,N-heteropentacene10 11.2

TiO2/Perovskite /P3HT11 6.6

TiO2/Perovskite /DFTAB12 7.2

TiO2/Perovskite /DEPT-SC13 9.7

TiO2/Perovskite /HA-114 12.0

TiO2/Perovskite/N-phenylindole-diketopyrrolopyrrole15 10.0

SnOx/Perovskite /RCP16 17.3

TiO2/Perovskite /Chl-117 11.4

SnOx/PCBM/Perovskite /BTPA-TCNE18 16.9

TiO2/Perovskite /pBBTa-BDTs19 12.3

TiO2/Perovskite /DERDTS–TBDT20 16.2

TiO2/Perovskite /TP121 12.6

TiO2/Perovskite /SAF-OMe22 12.4

TiO2/Perovskite /TPE-4DPA23 9.1

TiO2/Perovskite /HTM Z3424 16.1

TiO2/Perovskite /Z101125 16.3

TiO2/Perovskite /ST126 15.4

TiO2/Perovskite /DPP27 10.8

TiO2/Perovskite/KR32128 19.0

Trux-OMeTAD/Perovskite/PCBM/ZnO29 18.6

PTAA/Perovskite/PS/C60/BCP30 20.4

Table S4. The maximized device performances of device based on MA and FAMA as absorber

layer.

Device

Configuration

Voc

[V]

Jsc

[mAcm-2]

FF

[%]

PCE

[%]

ITO/C60-SAM/MA based

perovskite/PDCBT/Ta-WOx/Au

1.06 21.4(20.7a) 77 17.5

ITO/C60-SAM/FAMA based

perovskite/PDCBT/Ta-WOx/Au

ITO/C60-SAM/SnOx/PC60BM/FAMA based

perovskite/PDCBT/Ta-WOx/Au

1.10

1.17

22.3(21.6a)

22.7(22.2a)

78

80

19.0

21.2

a Integrated photocurrent values from EQE characterization.

Fig. S2. UV-vis absorption spectra of glass/WOx and glass/Ta-WOx, and the corresponding real

pictures of these two inks.

Fig. S3. XPS spectra of WOx and Ta-WOx.

400 600 800 1000 1200 14000.0

0.1

0.2

WOx

Ta-WOx

Wavelength (nm)

Ab

so

rba

nce

Ta-WOx WOx

32 31 30 29 28 27 26 25

Ta(V) 4f7/2

Inte

nsity (

a.u

.)

Binding Energy (eV)

WOx

Ta-WOx

Ta(V) 4f5/2

Fig. S4. The XRD patterns of the Ta-WOx and WOx. All of the diffraction peaks can be indexed

to the pure hexagonal phase of WO3 (JCPDS card 33-1387). The XRD peak intensity of the

(001) plane is the major growth direction.

Fig. S5. ToF-SIMS of the two samples with and without Ta-WOx interfaces.

ITO glass

Perovskite

PDCBT

Au

Ta-WOx

0 2000 4000 6000 8000

101

102

103

104

105

CN-

S-

InO-

WO3

-

I2

- (PbI

3

-)

Au3

-

Inte

nsit

y (

co

un

ts)

Sputter time (s)

Au Active layer ITO

0 2000 4000 6000 8000

101

102

103

104

105

CN-

S-

InO-

WO3

-

I2

- (PbI

3

-)

Au3

-

Inte

nsit

y (

co

un

ts)

Sputter time (s)

HTL

Au Active layer ITOHTLa

b

ITO glass

Perovskite

PDCBT

Au

15 20 25 30 35 40 45 50 55 60 65 70

(001)

24.0

WO3 ICSD No. 84160

Ta2O

5 ICSD No. 108463

In

ten

sity

2 (°)

23.8

(001)

WOx

Ta-WOx

Fig. S6. AFM height profile of Ta-WOx on top of PDCBT (with RMS of 1.8 nm)

Fig. S7. a, Device architecture of the perovskite solar cell. b, Chemical structures of the hole-

transporting p-type polymers and n-type interface materials used in this study.

RMS: 1.8 nm

Ta-WOx/PDCBT

ITO glass

Perovskite

HTLs

Au

Ta-WOx

PDCBTP3HT

pDPP5T-2

C60-SAM(Phosphonic acid anchor group)

SnOx

PTB7

PC60BM

PffBT4T-2OD

PDBT-T1

a b

Fig. S8. The j-V characteristic of the perovskite solar cells with PDCBT/Ta-WOx, doped spiro-

MeOTAD, and undoped spiro-MeOTAD HTMs under the identical fabrication parameters.

0 2 4 6 8 10 12 14 16 18 206

9

12

15

18

21

24

C60-SAM/MA

C60-SAM/FAMA

C60-SAM/SnOx/PC60BM/FAMA

Po

we

r C

on

ve

rsio

n E

ffic

ien

cy (

%)

Number of Measured Devices

Fig. S9. Efficiencies distribution of 20 perovskite solar cells using different composition

absorber and varied ETMs.

0.0 0.2 0.4 0.6 0.8 1.0

-20

-10

0

10

20

PDCBT/Ta-WOx/Au

Undoped Spiro-MeOTAD/Ta-WOx/Au

Doped Spiro-MeOTAD/MoOx/Au

Voltage (V)

Cu

rre

nt d

en

sity (

mA

/cm

*cm

)

400 500 600 700 800 900 1000 1100

MA

FAMA

Wavelength (nm)

Norm

aliz

ed

abso

rbance

Fig. S10. UV-vis absorption spectra of FAMA and MA based perovskite, respectively.

400 500 600 700 8000

20

40

60

80

100

Inte

gra

ted

Cu

rre

nt

(mA

/cm

2)

Wavelength (nm)

Exte

rna

l Q

ua

ntu

m E

ffic

ien

cy (

%)

0

5

10

15

20

25

30

MA

FAMA

Fig. S11. EQE and integrated current spectrum of the devices with FAMA and MA based

perovskite as absorber layer.

Fig. S12. a, External quantum efficiency spectrum of the devices using PDCBT/Ta-WOx and

pDPP5T-2/Ta-WOx as HTMs, respectively. b, UV-vis absorption spectra of PDCBT, pDPP5T-2,

and MAPbI3, respectively.

400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

Wavelength (nm)

Absorb

ance (

a.u

.)

MAPbI3

DPP

PDCBT

400 500 600 700 8000

20

40

60

80

100

PDCBT/Ta-WOx

pDPP5T-2/Ta-WOx

Wavelength (nm)

Exte

rna

l Q

ua

ntu

m E

ffic

ien

cy (

%)

800 820 840 8600.0

0.2

0.4

0.6

0.8

1.0

Wavelength (nm)

Exte

rnal Q

uantu

m E

ffic

iency (

%)

a.

b.

Fig. S13. Unencapsulated device photostability tests under continuous one sun illumination. The

corresponding variations in FF (a), Voc (b), and Jsc (c) variation of the HTM stacks based on a

C60-SAM with a strong binding between the phosphonic acid to the oxide surface as ETM: spiro-

MeOTAD/MoOx/Au (yellow), PDCBT/MoOx/Au (green) and PDCBT/Ta-WOx/Au (black).

0 250 500 750 10000.2

0.4

0.6

0.8

1.0

1.2

No

rmaliz

ed F

F

Time (h)

0 250 500 750 10000.2

0.4

0.6

0.8

1.0

1.2

No

rmaliz

ed V

oc

Time (h)

0 250 500 750 10000.2

0.4

0.6

0.8

1.0

1.2

No

rma

lize

d J

sc

Time (h)

cba