A theoretical study of the photoelectric properties of lead-free Ca2In4X8 (X = S, Se, Te) via density functional theory

Abstract

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.