Deciphering halide ion migration and performance loss in wide-bandgap perovskite solar cells: connection, mechanism, and solutions

Wide-bandgap (WBG, ≥1.60 eV) mixed-halide perovskites with tunable bandgaps are pivotal for advancing tandem photovoltaics (PVs). However, WBG perovskite solar cells (PSCs) suffer from severe performance loss, often directly linked to halide ion migration (HIM). While strategies to suppress HIM have improved device properties, the underlying relation between HIM and device performance remains ambiguous and contentious. In this minireview, we summarize and evaluate the origins of voltage (V_OC) and current (J_SC) losses and critically assess their correlation with HIM-driven issues, such as phase heterogeneity and carrier funneling. Furthermore, we propose research priorities to resolve this matter in a nutshell: (i) mechanistic investigation of iodide(I)-rich terminal (∼1.60 eV) domains, including spatiotemporal resolved mapping and interfacial carrier dynamics and (ii) regulation strategies, such as additive and interface engineering, to mitigate adverse effects caused by HIM. By elucidating the mechanistic interplay between HIM and performance decay, this work aims to offer more powerful guidance for efficient and photostable WBG perovskite-related PVs.