Light‐Induced Phase Segregation in Mixed‐Halide Perovskites: Reconciling Mechanistic and Thermodynamic Models

ABSTRACT Mixed‐halide perovskites often undergo reversible phase segregation under illumination, yet the origin and the material properties governing this process remain debated. Several driving forces for halide segregation have been proposed, including polaronic strain, bandgap effects, internal electric fields, and photoinduced redox reactions. These are often treated as competing frameworks for the interpretation of seemingly similar experimental observations. Here, we argue that progress in the field is limited due to an intertwining of kinetic and thermodynamic aspects of segregation and encourage the use of a generalized thermodynamic description in which different microscopic models correspond to different ways of modifying the free‐energy balance under illumination. We therefore analyze the assumptions, predictions, and experimental signatures of the most widely discussed mechanisms. We further identify key limitations in current experimental approaches, mostly associated with an overreliance on photoluminescence as a characterization tool, and how variations in experimental conditions further obscure comparison across studies. By outlining descriptors and experimental strategies, we provide a basis for systematically testing competing mechanisms. This work thus aims to move the field from parallel model interpretations toward a more unified and quantitative understanding of halide segregation in perovskites.