Synthesis, Crystal Structure, UV-Vis Adsorption Properties, Photoelectric Behavior, and DFT Computational Study of All-Inorganic and Lead-Free Copper Halide Salt K₂Cu₂Cl₆

In this study, all-inorganic copper halide salt K₂Cu₂Cl₆ single-crystal and thin films were prepared. The single-crystal diffraction data belonged to the monoclinic K₂Cu₂Cl₆ (space group = P ₂(1)/C, unit cell parameters of a = 4.0340 Å, b = 13.7987 Å, c = 8.7445 Å, α = 90.000, β = 97.123, and γ = 90.000). As far as we know, this is the first study of the copper halide salt K₂Cu₂Cl₆ for optoelectronic applications. The band gap of K₂Cu₂Cl₆ is calculated to be approximately 1.85 eV. A low-cost photodetector based on the K₂Cu₂Cl₆ thin film was efficient under different monochromatic light from 330 to 390 nm with different chopping frequencies (1.33-30 Hz). Density functional theory (DFT) computational results indicate that the valence bands (VBs) and conduction bands (CBs) are shifted up in energy using the orbital-dependent correction to the DFT energy. Partial density of states reveals that the VBs and narrow CBs are derived from the hybrid orbitals of Cu²⁺ 3d and Cl^- p, respectively.