Edge electron state modulation achieving tin-based perovskite solar cells with efficiency over 15%

The heavy p-doping effect and intrinsic defects of tin-based perovskites are two major challenges, which greatly limit the device performance of tin-based perovskite solar cells (PSCs). In this study, a novel n-type organic small molecule dopant, namely, NDI2HD-Br₂, is proposed to synergistically alleviate the intrinsic severe p-type self-doping and passivate the Sn-related defects of tin-based perovskites. Specifically, the carbonyl groups (C=O) with high electron density in the NDI2HD-Br₂ can donate additional electrons to the perovskite band edge, resulting in the conversion of the tin-based perovskite from a p-type to a weak n-type semiconductor (i.e., up-shifting the Fermi level by 0.15 eV). By this way, we achieve a power conversion efficiency (PCE) of 15.01% with a high open-circuit voltage of 0.95 V for the tin-based PSCs. Moreover, the NDI2HD-Br₂ incorporated devices exhibit excellent long-term stability that maintains 81% of the initial PCE after 1500 h of storage in a nitrogen environment. This study provides a new pathway to modulate electronic structures and passivate intrinsic defects of tin-based perovskites for efficient and stable solar cells.