Operando stress monitoring reveals critical reversibility thresholds in UV-degraded perovskite solar cells

The degradation of perovskite solar cells (PSCs) under ultraviolet (UV) irradiation involves complex multiphysics interactions, yet the dynamic evolution of ion migration and defect generation at the interfaces remains elusive. This work employs embedded dual fiber Bragg grating sensors to monitor the operando evolution of interfacial tension within the perovskite active layer during UV exposure. Through control of the energy and intensity of UV light, a relationship was established between the evolution of interfacial stress in the perovskite and the decline in device power conversion efficiency (PCE), a degradation attributed to methylammonium cation escape. The stress evolution proceeds in two distinct stages: an initial phase of rapid stress accumulation, followed by a period of relaxation and stabilization. Dark recovery techniques show that efficiency loss is reversible during the initial stage but becomes irreversible in the succeeding phase. A critical PCE threshold was identified at the intersection of the stress evolution and PCE decay curves, serving as the primary diagnostic indicator for the device recovery window. Strategic intervention at this reversible phase increases the recoverable window by 140%, demonstrating the effectiveness of stress-guided recovery techniques for improving PSCs stability. Consequently, real-time stress monitoring enables a predictive failure framework that lays the groundwork for improving the long-term reliability of perovskite photovoltaics via mechanism-based maintenance protocols.