Unveiling the impact of photoinduced halide segregation on performance degradation in wide-bandgap perovskite solar cells

Halide segregation under light exposure is a critical factor contributing to performance degradation of wide-bandgap perovskite solar cells (WBG PSCs). While this degradation has been traditionally linked to deficits in open-circuit voltage, our study identifies an initial sharp loss in short-circuit current density (J_SC) as a significant inducement in the efficiency decline, particularly within the first ∼240 seconds of light irradiation. By systematically varying the thickness of perovskite films, we observed two distinct migration modes of halide ions. Our results indicate that the rapid formation of I-rich terminal domains (∼760 nm; ∼1.63 eV) plays a pivotal role in the J_SC loss, rather than the gradually red-shifted phases typically seen in perovskite films. We found that in thicker films (∼420 nm), significant compressive strain in the crystal-stacked structure accelerates the formation of these I-rich domains. In contrast, thinner films (∼190 nm) exhibit a structure of vertically oriented crystals, despite having higher defect concentration and more pronounced photoinduced halide segregation, which enhances carrier extraction and stabilizes J_SC output. These findings highlight the importance of crystallization regulation in perovskite films as a strategy to mitigate J_SC loss and improve the photostability of WBG PSCs. Our research provides new insights into the mechanisms behind halide segregation and its impact on device performance, offering practical solutions for enhancing the long-term performance of WBG PSCs.