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

The grain sizes of soft CHNHPbI (MAPbI) thin films and the atomic contact strength at the MAPbI/P3CT-Na interface are manipulated by varying the drying time of the saturated MAPbI 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 ( ) and increased fill factor (FF) are mainly due to the formation of merged MAPbI grains. Besides, the open-circuit voltage ( ) 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 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 grains while keeping the contact quality at the MAPbI/P3CT-Na interface, which boosts the device performance and lifespan of the resultant perovskite photovoltaic cells.