Formation of p-type Cu₃BiS₃ absorber thin films by annealing chemically deposited Bi₂S₃–CuS thin films

Formation of the ternary compound Cu₃BiS₃ during annealing of chemically deposited CuS (∼0.3 μm) films on Bi₂S₃ film (∼0.1 μm on glass substrate) is reported. The interfacial atomic diffusion leading to the formation of the compound during the annealing is indicated in x-ray photoelectron depth profile spectra of the films. The formation of Cu₃BiS₃ (Wittichenite, JCPDS 9-488) is confirmed by the x-ray diffraction (XRD) patterns. The films are optically absorbing in the entire visible region (absorption coefficient 4 × 10⁴ cm⁻¹ at 2.48 eV or 0.50 μm) and are p-type with electrical conductivity of 10²−10³ Ω⁻¹ cm⁻¹. Potential applications of these films as optical coatings in the control of solar energy transmittance through glazings and as a p-type absorber film in solar cell structures are indicated.