Insight into the optoelectronic and thermochemical properties of LiXY2 (X = Ga, Ti; Y = S, Se, Te): a DFT study

Structure, optoelectronic, and thermochemical characteristics of Li-based chalcopyrite materials LiXY₂ (X = Ga, Ti; Y = S, Se, Te) are studied using DFT approach. Geometry optimization and modeling of LiXY₂ are performed using several functionals like B3LYP/LANL2DZ, B3LYP/SDD, B3LYP/DEF2TZVP, CAM-B3LYP/LANL2DZ, CAM-B3LYP/SDD, CAM-B3LYP/DEF2TZVP, APFD/LANL2DZ, APFD/SDD, and APFD/DEF2TZVP within DFT framework and made a comparative analysis. It is found that functional B3LYP/DEF2TZVP provides the most suitable result. Using B3LYP/DEF2TZVP, the HOMO–LUMO gaps of LiGaS₂, LiGaSe₂ and LiGaTe₂ are determined as 3.34, 3.08, and 2.72 eV, respectively, whereas for LiTiS₂, LiTiSe₂, and LiTiTe₂, it is found as 2.71, 2.77, and 1.79 eV correspondingly, signifying their possible uses in optoelectronic devices and solar cells. It also specifies that the replacement of Ga with Ti in the host materials helps in the reduction of the energy gap, which exhibits its better absorption ability. The vertical ionization potential (VIP) as well as vertical electron affinity (VEA) of LiTiY₂ are found lesser in magnitude in comparison with LiGaY₂. LiTiTe₂ exhibits the lowest VIP, whereas LiGaTe₂ displays the maximum VEA, which indicates that LiTiTe₂ and LiGaTe₂ are suitable materials for hole and electron infusion, respectively. LiGaY₂ shows a high electronegativity as compared to LiTiY₂, which indicates that LiGaY₂ offers advantages to enhance electron and hole mobility. The refractive index for LiGaY₂ increases from LiGaS₂ to LiGaSe₂ to LiGaTe₂, while for LiTiY₂, the highest and the lowest magnitudes are observed for LiTiTe₂ and LiTiSe₂, respectively. Thermochemical properties of LiXY₂ are also computed.

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