FLOW-ENABLED SELF-ASSEMBLY OF FORMAMIDINIUM LEAD IODIDE LARGE GRAINS FOR HIGH-PERFORMANCE PEROVSKITE SOLAR CELLS

摘要

Organolead halide perovskite solar cells have been recognized as promising candidates for high-efficiency solar cells with low costs, the power conversion efficiencies (PCEs) of which have been exceeding 20 %. Compared to conventional methylammonium lead iodide (MAPbO3) perovskites, formamidinium lead iodide (FAPbI3) perovskites with low bandgaps, good stability, and negligible hysteresis have recently been widely explored. The major energy loss in organolead halide perovskite solar cells is correlated with the non-radiative charge carrier recombination due to the formation of charge trap states at grain boundaries of perovskite crystals. Therefore, fabricating high-quality perovskite thin films with large crystal sizes is beneficial for decreasing grain boundaries, reducing structural defects, suppressing non-radiative recombination loss, and eventually enhancing the photovoltaic performances. For solution-processable perovskite thin films, the key to large-sized perovskite grains is controlling the nuclear generation and crystal growth during the solvent evaporation. Controlled evaporation induced self-assembly (CESA) has been widely utilized to regulate solvent evaporation process, thereby entailing highly-ordered deposition structures of various nonvolatile nanomaterials (i.e., DNA, micelles, colloidal nanoparticles, and block copolymers). As a movable CESA, flow-enabled self-assembly offers promising route to controlling the formation of large-area thin films. Herein, we report a facile strategy of fabricating large FAPbI3 crystal grains by FESA, leading to high-efficiency perovskite solar cells. The crystal growth kinetics of the FAPbI3 large grains in the FESA process were also elucidated. This strategy can stand out as an effective strategy for fabricating large-sized, high-quality, and good-stability organolead halide perovskite thin films.