L‐histidine‐Modulated Self‐Assembled Monolayers for Efficient and Mechanically Stable Flexible Perovskite Solar Cells

Flexible perovskite solar cells (F‐PSCs) based on inverted architectures with self‐assembled monolayer (SAM) hole contacts have recently achieved remarkable efficiency improvements, yet interfacial defects and mechanical fragility at the buried SAM/perovskite interface continue to limit both efficiency and operational durability. Here, we demonstrate that L‐histidine serves as multifunctional molecular modulator at the buried SAM/perovskite interface. Proton transfer from the phosphonic acid head group of the carbazole‐based SAM to the amino group of L‐histidine generates strong interfacial dipole that improves energy‐level alignment and hole extraction, while π–π stacking between the imidazole ring and the carbazole unit stabilizes the molecular assembly. The amino and carboxyl groups of L‐histidine further coordinate with undercoordinated Pb ²⁺ and halide ions to passivate buried interface defects and promote uniform perovskite crystallization. For flexible applications, the compliant aliphatic backbone of L‐histidine transforms the rigid SAM/perovskite contact into a mechanically compliant interface, eliminating interfacial voids and relieving residual tensile strain. These synergistic effects yield a best power conversion efficiency of 23.47% for F‐PSCs, along with enhanced operational stability (95.56% retention after 548 h) and mechanical durability (95.06% retention after 1000 bending cycles at 5 mm radius).