Effects of drying time on the formation of merged and soft MAPbI 3 grains and their photovoltaic responses.

The grain sizes of soft CH 3 NH 3 PbI 3 (MAPbI 3 ) thin films and the atomic contact strength at the MAPbI 3 /P3CT-Na interface are manipulated by varying the drying time of the saturated MAPbI 3 precursor solutions, which influences the device performance and lifespan of the resultant inverted perovskite photovoltaic cells. The atomic-force microscopy images, cross-sectional scanning electron microscopy images, photoluminescence spectra and absorbance spectra show that the increased short-circuit current density ( J SC ) and increased fill factor (FF) are mainly due to the formation of merged MAPbI 3 grains. Besides, the open-circuit voltage ( V OC ) of the encapsulated photovoltaic cells largely increases from 1.01 V to 1.15 V, thereby increasing the power conversion efficiency from 17.89% to 19.55% after 30 days, which can be explained as due to the increased carrier density of the MAPbI 3 crystalline thin film. It is noted that the use of the optimized drying time during the spin coating process results in the formation of merged MAPbI 3 grains while keeping the contact quality at the MAPbI 3 /P3CT-Na interface, which boosts the device performance and lifespan of the resultant perovskite photovoltaic cells.