Bilateral Interface Engineering toward Efficient 2D–3D Bulk Heterojunction Tin Halide Lead-Free Perovskite Solar Cells

As a promising substitute for toxic lead-based perovskite, tin (Sn)-based halide perovskite has drawn much attention for photovoltaic applications. However, unsatisfied open-circuit voltage (VOC) and fill factor (FF) values of the available Sn-based perovskite solar cells (PSCs) remain a lingering cloud. In this work, we report a bilateral interfacial engineering strategy to fabricate 2D–3D bulk heterojunction Sn-based perovskite solar cells. Specifically, large cation PEAI and bifunctional LiF are evaporated at the bilateral interfaces of a FASnI3 film. The presence of PEAI improves the VOC and FF of the PSCs via improved surface coverage and the formed 2D–3D bulk heterojunction structure, while the bifunctional LiF (i) lowers the work function of PEDOT:PSS and (ii) facilitates hole extraction at the ITO/PEDOT:PSS interface. This strategy enabled a power conversion efficiency (PCE) of 6.98% with a VOC of 0.47 V and FF of 0.74. Our findings will add critical building bricks toward efficient Sn-based PSCs.