Synthesis, Crystal Structure, UV–Vis Adsorption Properties, Photoelectric Behavior, and DFT Computational Study of All-Inorganic and Lead-Free Copper Halide Salt K(2)Cu(2)Cl(6)

[Image: see text] In this study, all-inorganic copper halide salt K(2)Cu(2)Cl(6) single-crystal and thin films were prepared. The single-crystal diffraction data belonged to the monoclinic K(2)Cu(2)Cl(6) (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 K(2)Cu(2)Cl(6) for optoelectronic applications. The band gap of K(2)Cu(2)Cl(6) is calculated to be approximately 1.85 eV. A low-cost photodetector based on the K(2)Cu(2)Cl(6) 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 Cu(2+) 3d and Cl(–) p, respectively.