Co‐Self‐Assembled Interface Engineering Assisted for Bend‐Resistant and Efficient Flexible Perovskite Solar Cells

Abstract Flexible perovskite solar cells (F‐PSCs) have attracted considerable interest for their superior mechanical flexibility. Nonetheless, cryptic bottom‐interface defects hinder further improvements in device performance. Here, a co‐self‐assembled monolayer (Co‐SAM) engineering strategy is implemented by integrating 4‐nitrophenyl phosphate (PNPP) into [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) butyl] phosphonic acid (Me‐4PACz) to improve the NiO x /perovskite (PVK) interface. This technique enhanced the surface uniformity and hydrophilic nature of the NiO x /Me‐4PACz, while promoting favorable growth of PVK crystal orientation. Furthermore, the PNPP effectively mitigates the generation of defects at the NiO x surface and the underlying PVK, ultimately significantly improving the interfacial charge transfer efficiency. Consequently, the efficiency of F‐PSCs rose from 21.46% to 23.66%. Due to better stress distribution within the PVK and stronger adhesion at the NiO x /PVK boundary, the F‐PSCs retained 80% of their original efficiency even after undergoing 10 000 bending cycles. Notably, PNPP exhibited an outstanding capacity to capture PbI 2 , contributing to the potential for reducing Pb leakage of the device under operational conditions.