Supplementary Information for
Abhishek K. Chauhan, Soumya Ranjan Pal, Pankaj Kumar, Sanjay K. Srivastava, Saravanan Muthiah
Advance Materials and Devices Division, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110012, India
Materials used for device preparation
Fluorine doped tin oxide (FTO) substrates, titanium isopropoxide, methylamine, hydroiodic acid, lead chloride, poly(3-hexylthiophene) (P3HT), dimethyl formamide (DMF), ethanol, chloroform, Ag shots. All materials were purchased from Sigma-Aldrich, USA
Synthesis of CH3NH3I
24 ml of methylamine (33 wt% in absolute ethanol) was reacted with 10 ml of hydroiodic acid (57 wt% in water) in 250 ml round bottom flask at 0oC for 2 h under continuous stirring. The solution was put in a rotary evaporator where solvent was evaporated at 50oC for 1 h and yellowish white powder of CH3NH3I was obtained which was re-dissolved in 80 ml of absolute ethanol and re-precipitated by addition into 300 ml of diethyl ether. The white precipitate of CH3NH3I was dried in vacuum oven overnight at 70oC and used for device preparation.
Device preparation
The solar cells have been prepared on cleaned and patterned FTO coated glass substrates. The mild acidic solution of titanium isopropoxide was spin coated on the FTO substrates and followed by thermal annealing at 500±1oC for 30 min to achieve around 70 nm of compact TiO2 planar layer. Thermal annealing was carried out in a muffle furnace from Metrex Scientific Instruments Pvt. Ltd. India, with microprocessor based temperature controller. Before the samples were placed inside the furnace the furnace was set and brought to 500±1oCby the temperature controller. Once the temperature was attained, the samples were inserted inside the furnace slowly-slowly that caused some reduction in furnace temperature. But once the samples wereplaced and furnace door was closed the temperature reached again 500±1oC within few minutes. Now the samples were kept at 500±1oC for 30 min. and then furnace was allowed to cool down and the samples were taken out slowly-slowly and allowed to cool down.The mixed halide CH3NH3PbI3-xClx perovskite precursor was prepared via intermixing of PbCl2 (0.8 M) andCH3NH3I (2.4 M) in 1:3 molar ratio (38.9 wt%) in dimethyl formamide (DMF). This solution was diluted with pure DMF to formulate its 24.1, 17.5 and 13.7 wt% solutions. The solutions have been designated as S1 (13.7 wt%), S2 (17.5 wt%), S3 (24.1 wt%) and S4 (38.9 wt%). All the precursors were spin coated on compact TiO2 coated FTO substrates and cured at 110±1oC for 90 min, which resulted the final thicknesses of the films to be 50±5 nm, 95±5 nm, 200±5 nm and 310±5 nm respectively for S1, S2, S3 and S4 precursors.For curing the samples were placed on a hot plate from Tarsons, India with microprocessor based temperature controller. Before samples were placed on the hot plate it was brought to 110±1oC and then only the samples were placed on it for curing.The thicknesses of the perovskite films were measured using stylus type thickness profiler.15 mg/ml solution of P3HT in chloroform was spin coated as HTM on the perovskite films which was finally followed by ~ 100 nm of Ag deposition by thermal evaporation through shadow masks to complete the device. For mesoscopic solar cells a thin layer of ~ 130 nm of mesoporous TiO2 was deposited by spin coating from TiO2 paste on the compact TiO2-bl layer. Themesoporous TiO2 films were annealed at 500±1oC for 60 min.The deposition procedure of rest of the films on mesoporous TiO2 was same as that used for planar heterojunction solar cells based on corresponding precursor solutions.
Characterization
Thin films of mixed halide perovskite have been characterized by X-ray diffraction (XRD), UV-vis absorption spectroscopy and scanning electron microscopy (SEM). The photovoltaic performance for solar cells was measured from their J-V characteristics measured under 100 mW/cm2 illumination of AM1.5 G solar simulator.
Fig. SI1. Photographs of the planar samples coated with different wt% precursor solutions. (a), (b), (c) and (d) are the photos of the samples coated with S1, S2, S3 and S4 respectively, taken after 5 min. of placing them on the hot plate for thermal annealing. (e), (f), (g) and (h) are the photos of the same samples taken after 90 min. on the hot plate.
Fig. SI2. SEM images of perovskite films coated on (a) bare FTO substrate and (b) compact TiO2 coated FTO substrate using S4 solution.
Fig. SI3. Contact angle of water on (a) bare FTO and (b) compact TiO2 coated FTO substrates. The TiO2 coating at FTO clearly has higher surface energy compared to bare FTO substrate.
Fig. SI4. EQE graphs of one of the planar S4 samples measured with and without white light bias.
Fig. SI5. Zoom out SEM images of the perovskite films prepared on planar TiO2-bl coated FTO substrates using S1 (a), S2 (b), S3 (c) and S4 (d) precursor solutions.
Fig. SI6. Photographs of a sample coated with mixed halide perovskite, taken after (a) 0 h and (b) 184 h of air exposure.
Fig. SI7. Schematic structure of the mesoscopic Glass/FTO/TiO2-bl/TiO2-mp/CH3NH3PbI3-xClx/P3HT/Ag PvSCs studied here.
Fig. SI8. Degradation profiles of Jsc (a), Voc (b) and FF (c) of mesoscopic PvSCs based on different perovskite precursors.The solar cells were not encapsulated.
Fig. SI9. Degradation profiles of Jsc (a), Voc (b) and FF (c) of mesoscopic PvSCs in outdoor conditions under natural sunlight. The solar cells were not encapsulated.
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