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

Abstract

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 Pb²⁺ 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).