Electronic Supplementary Information

Annealing-free perovskite films with solvent engineering for efficient

perovskite solar cells

Xiang Fang,a Yihui Wu,b Yongting Lu,a Yue Sun,a Shuai Zhang,a Jing Zhang,a Wen-Hua Zhang,b Ningyi Yuan*a and Jianning Ding*a

a School of Materials Science and Engineering, Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University; Changzhou, 213164, Jiangsu, ChinaJiangsu Key Laboratory for Photovoltaic Engineering and Science, Changzhou University, Changzhou, 213164, Jiangsu, ChinaE-mail: dingjn@cczu.edu.cn; nyyuan@cczu.edu.cn

b Micro/Nano Science and Technology Center, Jiangsu University, Zhenjiang, 212013, Chinac Sichuan Research Center of New Materials, Institute of Chemical Materials, China Academy of Engineering Physics, 596 Yinhe Road, Shuangliu, Chengdu 610200, Sichuan, China

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2016

Experimental sectionPreparation of perovskite precursor solutions

The anhydrous N,N-dimethylformamide (DMF, Sigma Aldrich) and Dimethylacetamide (DMAc, Sigma Aldrich) are mixed with dimethyl sulfoxide (DMSO, Sigma Aldrich) or N-Methyl-2-pyrrolidone (NMP, Sigma Aldrich), respectively. And four kinds of co-solvents are obtained, including DMF/DMSO (optimized vol% 2:3), DMAc/DMSO (optimized vol% 2:3), DMF/NMP (optimized vol% 4:1) and DMAc/NMP (optimized vol% 4:1). CH3NH3I and PbI2 (Sigma-Aldrich) (molar ratio 1:1) are added in the above-mentioned co-solvents for 1.2 M CH3NH3PbI3 (MAPbI3) solutions. The resulting precursor solutions are filtered with PTFE 0.2 μm filters following stirred overnight at 70 °C.

Fabrication of devices

Fluorine-doped SnO2 (FTO) transparent conducting glasses are ultrasonically washed in deionized water, acetone and isopropanol for 30 min, respectively, and then treated by oxygen plasma for 10 min. The compact TiO2 blocking layer is spin-coated on the substrate at 3000 rpm for 30 s and the film is annealed at 500 °C for 1 h. A mesoporous scaffold is formed by spin coating of TiO2 paste (Dyesol, 20 NR-D) dissolved in ethanol at a concentration of 200 mg mL-1, followed by sintering at 500 °C for 30 min. After cooling down to room temperature (RT), the perovskite precursor solutions are spin-coated over the mesoporous TiO2 layer with a process of 1000 rpm for 10 s and 5000 rpm for 40 s. After reaching high-speed rotation for about 10 s, a certain amount of toluene (500 μL for DMSO based devices and 50 μL for NMP based devices) is dripped on the substrates. The samples are with or without thermal annealing at 100 °C for 5 min. Subsequently, the hole-conductor material (HTM) (spiro-OMeTAD, (2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′- spirobifluorene)) is spin-coated on perovskite layer at 4000 rpm for 30 s. The preparation of spiro-OMeTAD solution is followed by the literature. 520 mg of lithium-bis- (trifluoromethanesulfonyl) imide (Li-TFSI, 99.95%, Sigma-Aldrich) is dissolved in 1 mL acetonitrile (99.5%, Sigma) to form a Li-TFSI stock solution. The HTM solution is prepared by dissoving 72.3 mg spiro-OMeTAD (98%, Feiming Technology Co., Ltd.) in 1 mL chlorobenzene (99%, Sigma-Aldrich)., with addition of 28.8 μL 4-tert-butylpyridine (96%, Aladdin) and 17.5 μL Li-TFSI solution. Finally, gold electrode with thickness of 80 nm is thermally evaporated on top of the device through a shadow mask with 0.2 cm2 active area.

Characterization

Field emission scanning electron microscope (FESEM, Philips XL30 FEG) is applied to analyze the morphology of perovskite films. The crystal structures are explored by X-ray diffraction (XRD) analysis with Cu Kα radiation (D/max 2500 PC, Rigaku Corporation, Japan; 2theta/theta, λ = 0.1541 nm) at 40 kV. UV-vis absorption spectra of samples are recorded on a UV5800 Spectrophotometer and the time-resolved photoluminescence (TRPL) decay is measured on a LifeSpecⅡfluorescent spectrometer (Hamamatsu, Edinburgh, UK). The ultraviolet photoelectron spectroscopy (UPS) is conducted with a SPECS Microwave UV Light Source (He I = 21.2 eV).The photovoltaic performance of the solar cells are measured using a Keithley Model 2400 multisource meter (Cleveland, OH, USA) under one sun (AM 1.5G, 100 mW cm-2) illumination with a solar simulator (500 W Xe lamp) (SAN-EI ELECTRIC XES-40S1, Japan) employed as the light source. All measurements are performed in air at room temperature.

Tabel S1 Examples of perovskite solar cells based on perovskite films fabricated at room temperature.

Implementation method

Precursor solvent

Anti-solvent Device configuation PCE ref

Humid air exposure GBL/DMSO tolueneITO/PEDOT:PSS/CH3NH3PbI3 nanorods/PC60BM/rhodamine/

Ag16.83 % 27

Air Exposure (two-step spin-coating)

DMF2-propanol

ITO/TiO2/CH3NH3PbI3/Spiro-OMeTAD/Ag

15.6 % 26

Water-vapor annealing

DMF chlorobenzeneITO/PEDOT:PSS/CH3NH3PbI3/

PCBM-PDINO/Al16.39 % 28

Mixed-solvent-vapor annealing (DMF/ chlorobenzene)

DMFITO/PEDOT:PSS/MAPbI3-

xClx/PCBM/LiF/Al16.41 % 29

Anti-solvent assisted crystallization

DMF/DMSOdichloromethane, chlorobenzene,

toluene

FTO/bl-TiO2/ TiO2/ CH3NH3PbBr3/spiro-

OMeTAD/Au7.54 % 30

Anti-solvent induced instant-crystallization

GBL/DMSO ethyl acetateFTO/NiO/

CH3NH3PbI3/PCBM/BCP/Ag15.58 % 31

Fig.S1 SEM images of MAPbI3 perovskite films prepared from co-solvents of DMF/DMSO, DMAc/DMSO, DMF/NMP and DMAc/NMP with different ratios and magnifications.

Fig. S2 AFM images of MAPbI3 perovskite films prepared from co-solvents of (a) DMF/DMSO, (b) DMAc/DMSO, (c) DMF/NMP, (d) DMAc/NMP.

Fig. S3 UV-vis absorption spectra of perovskite films prepared with different co-solvents.

Fig. S4 (a) The cut-off edge at high binding energy region and (b) valence band edge at low binding energy region of MAPbI3 UPS spectra based on different co-solvents. (c) The energy level structure of the as prepared perovskite films.

Fig. S5 EQE spectra of the perovskite solar cells based on different precursor solvents

Fig.S6 J-V characteristics of perovskite solar cells fabricated from different co-solvents, including reverse and forward scan. (a) DMF/DMSO, (b) DMAc/DMSO, (c) DMF/NMP, (d) DMAc/NMP

Fig.S7 SEM images of perovskite films made from DMAc/NMP. (a) without annealing; (b) annealing at 100℃ for 5

min.

(a) (b)

Fig. S8 Digital photographs of thin films formed from DMAc/DMSO and DMAc/NMP with different lay-out time at room temperature.

Fig. S9 Efficiency evolution of the perovskite solar cells kept in air (40% RH) at room temperature without

encapsulation for 21 days.

Fig. S10 XRD patterns of annealing-free perovskite films based on co-solvents of DMAc/DMSO and DMAc/NMP (a) with and (b) without toluene dripping.

(a)

(b)