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 (V-OC) 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 FASnI(3) film. The presence of PEAI improves the V-OC 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 V-OC of 0.47 V and FF of 0.74. Our findings will add critical building bricks toward efficient Sn-based PSCs.