The effect of selenium on the structural, morphology, optical, electrical properties of Cu2Te thin films for thermoelectric and photovoltaic applications

Abstract Synergistic optimization of optical and electrical properties of Cu2Te thin films was presented via doping with various content of selenium. Cu2Te1-xSex (x = 0.1, 0.2) thin films were successfully deposited by electron beam evaporation on silicon and glass substrate without any formation of non-stochiometric phases. X-ray diffractograms displayed that the deposited films have formed in a hexagonal single phase with a very slight shift owing to the incorporation of selenium, which is further affirmed by selected area electron diffraction pattern (SAED). The energy dispersive X-ray profile verified that selenium was successfully incorporated inside the Cu2Te matrix at the expense of Te. The cross-section view images illustrated that the thicknesses of studies films are about 200 nm. For x = 0.2, the films become smoother and grains are more identifiable of smaller size than Cu2Te0·9Se0.1, as visualized by FESEM and 3D AFM images. Over the wavelength range 200–2500 nm, the transmittance, reflectance, absorption edges, optical conductivity and electrical conductivity were reported. The values of band gap of both films are 1.45 and 1.65 eV. The refractive index of deposited films was analyzed by Single-oscillator model (WDD), oscillator energy (Eo), dispersion energy (Ed), and static refractive index (ns) were reported and discussed. Further, the ratio of free carrier concentration, the relaxation time (τ), third-order nonlinear susceptibility (χ(3)), nonlinear refractive index (n2), optical mobility (μopt) and optical resistivity (ρopt) greatly depend on the Se content. The electrical conductivity, thermoelectric power and power factors showed remarkable increase with increasing of selenium content. Solar cell device of the configuration glass/ITO/CdS/CdTe/Cu2Te1-xSex (x = 0.1, 0.2 mol)/Au was fabricated and demonstrated higher efficiency with increasing Se dopants.