Morphology-Induced Residual Stress Release Suppresses Light-Induced Phase Segregation in Mixed-Halide Perovskite Films

Phase segregation under light illumination in mixed-halide perovskite has attracted widespread attention. Meanwhile, the morphology of perovskite films plays an important role in the crystallinity, optoelectronic properties and device performance. Yet, the influence of morphology on phase segregation has not been systematically investigated. Here, we fabricate perovskite films with different surface morphologies and monitor the evolution of phase segregation under in situ illumination using multiphysical field luminescence imaging microscopy. Compared with flat films, the phase segregation in wrinkled films is significantly suppressed, which can be attributed to the release of the internal compressive stress. Furthermore, we propose a polaron-mediated phase segregation mechanism regulated by residual stress. Based on this model, we explain that perovskite films with different morphologies exhibit distinct phase segregation rates. These microscopic findings are critical for understanding the influence of strain on the phase segregation and guiding the future development of more stable wide-bandgap perovskite optoelectronic devices.