Thermal stabilization of defect charge states and finite-temperature charge transition levels

Point defects introduce localized electronic states that critically affect carrier trapping, recombination, and transport in functional materials. The associated charge transition level (CTLs) can depend on temperature, requiring accurate treatment of vibrational free energy contributions. In this work, we use machine-learned interatomic potentials to efficiently compute temperature-dependent (CTLs) for vacancies in MgO, LiF, and CsSnBr 3 . Using thermodynamic integration, we quantify free energy differences between charge states and calculate the vibrational entropy contributions at finite temperatures. We find that temperature significantly affects the (CTLs) across all three materials, with substantial energy level shifts in MgO and LiF over the investigated temperature ranges. Most notably, in CsSnBr 3 a neutral charge state becomes thermodynamically stable above 40K, introducing a Fermi-level window absent at 0K. We show that the widely used static, zero-kelvin defect formalism can miss both quantitative (CTL) shifts and the qualitative emergence of new stable charge states.