Abstract
Abstract The performance of perovskite solar cell devices is strongly dependent on the morphology, crystallinity, and phase purity of perovskite films. However, the complete conversion of PbI2 into perovskite and tailoring perovskite grain growth as well as its surface morphology are challenging in the conventional two-step sequential deposition method. In this study, a facile and effective approach was developed to improve perovskite conversion rate and film quality via in situ solvent assisted crystallization (ISAC) and compositional adjustment. It was found that in the presence of in situ solvent molecules, CH3NH3I (MAI) molecules readily intercalated in the PbI2 lattice to form small-grain (∼210 nm) MAPbI3 perovskite. By partially substituting MAI with a small amount of CH(NH2)2I (FAI), flat FAxMA1–xPbI3 films composed of much larger grains (∼450 nm) could be obtained due to the in situ formation and decomposition of (MA)2Pb3I8(DMSO)2 intermediates. Photovoltaic devices based on ISAC-FAxMA1–xPbI3 films exhibited an enhanced efficiency of 17.31% under AM 1.5G solar illumination at 100 mW cm−2 when compared to the devices based on ISAC-MAPbI3 films (14.30%), which can be mainly ascribed to the higher optical absorption and reduced defect density of the former. The results highlight the distinct effects of in situ solvent molecules on perovskite crystallization dynamics in various material systems and the importance of in situ solvent molecules in perovskite conversion, film morphology, and even device performance.
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