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

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 Pb²⁺ at the perovskite bottom surface, and anchor [PbX₆]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.