Engineering dynamic defect compensation in Sn-Doped In2O3 thin films for enhanced optoelectronic performance

Sn-doped In2O3 is a typical transparent conducting oxide, yet the mechanisms governing carrier suppression and functional degradation at high doping levels remain unclear. Here, defect engineering via controlled Sn incorporation is employed to tune dynamic defect compensation, enabling direct correlation between defect chemistry and optoelectronic functionality. A non-monotonic evolution of lattice parameter and carrier density reveals two distinct regimes. At low Sn concentrations, enhanced free-electron density induces a Burstein–Moss bandgap widening. Beyond a critical doping threshold, cooperative compensation mediated by Sn4+/Sn2+ coexistence and oxygen interstitials suppresses carrier density, activating competition between bandgap renormalization and the Burstein–Moss shift. Density functional theory calculations confirm the electronic impact of this defect complex. Remarkably, the evolution of photocurrent closely mirrors the methane sensing response, demonstrating that oxygen-related defects regulate charge-transfer dynamics. These findings establish dynamic defect compensation as a tunable design principle for engineering multifunctional transparent conducting oxides.