Selenizing Possibilities of Cu2HgSnS4—i.e., Cu2HgSn(SexS1−x)4 Compound Semiconductor: Potential Candidate for Solar Photovoltaics and Photodetectors

Herein, the authors report the optoelectronic and mechanical properties of Cu2HgSn(SexS1−x)4 alloy (0 ≤ x ≤ 1) using density-functional calculations. The alloy exhibits a range of bandgap 1.33–0.81 eV with small bowing 0.395, preserving direct nature at Γ point for any value of x. Hubbard parameter of ≈0.52 Ry is considered viewing the strongly correlated Cu-3d and Hg-4d orbitals, together with modified Becke–Johnson potential with spin–orbit coupling, to ensure accurate eigenvalues. When analyzing the charge density with a Bader charge analysis, decreasing ionic character with increasing Se concentrations is observed. The noticed elastic constant also satisfies the Born–Huang criteria and exhibits the ductile nature of Cu2HgSn(SexS1−x)4 system, making it a good candidate for flexible devices. The partial density of states highlights the dominance of Cu-d states in the valence band edge, while the conduction band edge majorly emerges with Se states. In addition, the absorption coefficient is also found at ≈104 cm−1, and a rising degree of polarization is seen when approaching x = 1. This study provides the potential of Cu2HgSn(SexS1−x)4 alloy system for a photo-absorber layer in graded and tandem thin-film solar cells together with low-bandgap Cu2HgSnSe4 as a suitable material for an infrared detector and thermoelectric applications.