Phosphine Interlayer Chemical Hardness Engineering via Crystallization Regulation for Wide‐Bandgap Perovskites and All‐Perovskite Tandems

Abstract In wide‐bandgap perovskite solar cells, light‐induced phase segregation of the perovskite film and non‐radiative recombination at the self‐assembled monolayers/perovskite interface severely compromise device efficiency and stability. Herein, an interfacial engineering strategy utilizing controllable Lewis base small molecules is proposed to ameliorate the Me‐4PACz/perovskite interface, enabling effective interfacial defect suppression and high‐quality perovskite crystallization. Theoretical and experimental results demonstrate that the optimized tris(2‐pyridyl)phosphine (TPP) molecule can simultaneously fill defects in Me‐4PACz self‐assembly, passivate undercoordinated Pb 2 ⁺ at the perovskite bottom surface, and anchor PbX 6 ⁴− to provide nucleation sites for inducing bottom‐up homogeneous crystallization. Consequently, the TPP‐treated single‐junction cell (1.77 eV) achieved a remarkable power conversion efficiency (PCE) of 20.46% with a high V OC of 1.34 eV, representing one of the highest reported efficiencies for this bandgap. The corresponding two‐terminal all‐perovskite tandem solar cells achieved a PCE of 29.71% (certified as 29.13%), with a V OC of 2.16 V and fill factor of 83.81%, meanwhile maintaining exceptional operational stability by retaining 91.96% of initial PCE after 850 h of maximum power point tracking under solar illumination.