Wearable Tin‐Based Perovskite Solar Cells Achieved by a Crystallographic Size Effect

Tin‐based perovskite solar cells (PSCs) demonstrate a potential application in wearable electronics due to its hypotoxicity. However, poor crystal quality is still the bottleneck for achieving high‐performance flexible devices. In this work, graphite phase‐C 3 N 4 (g‐C 3 N 4 ) is applied into tin‐based perovskite as a crystalline template, which delays crystallization via a size‐effect and passivates defects simultaneously. The double hydrogen bond between g‐C 3 N 4 and formamidine cation can optimize lattice matching and passivation. Moreover, the two‐dimensional network structure of g‐C 3 N 4 can fit on the crystals, resulting an enhanced hydrophobicity and oxidation resistance. Therefore, the flexible tin‐based PSCs with g‐C 3 N 4 realize a stabilized power conversion efficiency (PCE) of 8.56 % with negligible hysteresis. In addition, the PSCs can maintain 91 % of the initial PCE after 1000 h under N 2 environment and keep 92 % of their original PCE after 600 cycles at a curvature radius of 3 mm.