Defect Physics and Nanoscale Passivation Strategies in BaSi₂ Thin-Film Photovoltaics

Barium disilicide (BaSi₂) was identified as a promising silicon-based photovoltaic absorber due to its near-optimal bandgap, strong optical absorption, and earth-abundant composition. However, the performance of BaSi₂ thin-film solar cells was severely restricted by structural defects and interfacial instabilities that introduced localized electronic states and facilitated non-radiative recombination. These imperfections degraded carrier lifetime, mobility, and open-circuit voltage. This review systematically examined the formation, energetics, and electronic roles of intrinsic and extrinsic defects in BaSi₂ thin films, and evaluated nanoscale passivation strategies developed to mitigate defect-induced losses. Chemical, dielectric, and interfacial approaches were critically analyzed with emphasis on their underlying mechanisms, limitations, and integration potential. The convergence of in situ characterization, first-principles modeling, and data-driven process optimization was expected to enable predictive defect control and rational interface design, thereby advancing BaSi₂-based photovoltaics toward practical implementation.