• • Ca-Abz undergoes reversible photoisomerization from trans (E) to cis (Z) under UV illumination, with the Z isomer exhibiting stronger binding energy (−11.01 eV) than the E isomer (−10.99 eV), actively strengthening grain-boundary passivation under light.
• • The dynamic isomerization acts as a structural buffer, dissipating intergranular stress and regulating local lattice strain during cyclic illumination, preventing grain-boundary fragmentation and perovskite decomposition into Pb2+ and inactive phases.
• • The strategy addresses degradation under cyclic illumination (12 h light/12 h dark) and rapid temperature cycling (−40 to 85 °C), conditions not captured by conventional constant-illumination accelerated aging protocols.
• • This stimuli-responsive approach marks a paradigm shift from static passivators to dynamic interfacial regulators, utilizing UV energy to stabilize grain boundaries during lattice expansion, potentially extending PSC operational lifetime under real-world diurnal cycling.