A theoretical study of the photoelectric properties of lead-free Ca ₂ In ₄ X ₈ (X = S, Se, Te) <i>via</i> density functional theory

In recent years, perovskite materials have garnered significant attention in the field of optoelectronic devices and solar cells due to their excellent optoelectronic properties; however, the inherent toxicity and environmental adaptability limitations of lead-based perovskites severely constrain their development. To address these limitations, this study focuses on designing novel lead-free materials, the Ca₂In₄X₈ (X = S, Se, Te) compound system, by introducing inorganic cations (Ca²⁺) in synergy with low-toxicity chalcogen elements (S, Se, and Te). Density functional theory studies reveal that its highly symmetric In-X octahedral network structure effectively reduces lattice defects, endowing the material with high stability, excellent bandgap tunability, and high carrier mobility potential. Based on first-principles calculations, the properties of this system are systematically elucidated. Firstly, in-depth analysis of Ca₂In₄Te₈ indicates good lattice/thermal stability, with a bandgap close to the optimal range for photoelectric conversion. It exhibits high absorption in the visible light region; combined with band structure and carrier effective mass analyses, this suggests high potential for efficient solar-to-chemical energy conversion. Secondly, compared to lead-based perovskites limited by toxicity, Ca₂In₄S₈/Se₈/Te₈ significantly enhance light absorption performance while maintaining stability. Finally, electronic properties confirm that Ca₂In₄S₈/Se₈/Te₈ are direct bandgap semiconductors, with tunable bandgaps spanning the infrared-to-visible range. The band structures are dominated by hybridization of In-5p and X-p orbitals, providing a new pathway for developing environmentally friendly and efficient photovoltaic materials.