A Multifunctional Molecular Bridging Layer for High Efficiency, Hysteresis‐Free, and Stable Perovskite Solar Cells

Abstract At present, the dominating electron transport material (ETL) and hole transport material (HTL) used in the state‐of‐the‐art perovskite solar cells (PSCs) are tin oxide and 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD). However, the surface hydroxyl groups of the SnO 2 layer and the Li + ions within the Spiro‐OMeTAD HTL layer generally cause surface charge recombination and Li + migration, significantly reducing the devices' performance and stability. Here, a molecule bridging layer of 3,5‐bis(fluorosulfonyl)benzoic acid (FBA) is introduced onto the SnO 2 surface, which provides appropriate surface energy, reduces interfacial traps, forms a better energy level alignment, and, most importantly, anchors (immobilizes) Li + ions in the ETL, and consequently improves the device power conversion efficiency (PCE) up to 24.26% without hysteresis. Moreover, the device with the FBA passivation layer shows excellent moisture and operational stability, maintaining over 80% of the initial PCE after 1000 h under both aging conditions. The current work provides a comprehensive understanding of the influence of the extrinsic Li + ion migration within the cell on the device's performance and stability, which helps design and fabricate high‐performance and hysteresis‐free PSCs.