Properties of CuInGaSe thin films prepared by chemical spray pyrolysis

Polycrystalline films of semiconducting Cu(In_1-xGa_x)Se₂ (CIGS) quaternary alloy, one of the promising materials for photovoltaic applications, have been prepared by means of chemical spray pyrolysis (CSP). Copper, Indium and Gallium metal chlorides and Selenourea are used as constituent elements to prepare spray solution. Single phase CIGS films with chalcopyrite structure have been successfully grown on glass substrate at 350°C. The films have been characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Raman Spectroscopy and optical absorption in terms of deposition time from 5 minutes to 25 minutes. Hall studies were carried out to determine resistivity, mobility and carrier concentration in the film. All the deposited films were polycrystalline and showed single phase chalcopyrite structure with a preferred (112) orientation. Average grain size of 12.8 nm calculated from XRD spectra indicated that the films had a nanocrystalline structure. Chemical constituents present in the deposited CIGS films were identified using energy dispersive X-ray (EDX) analysis. The distinct peak in Raman spectra near 170 cm^-1 indicated the presence of CIGS. All the films exhibit direct band gap structure and their band gap values are found to be 1.40 to 1.64 eV. Optical absorption coefficients of the films are found to be over 10⁷cm^-1. Resistivity of the films varied from 0.4 Ohm-cm to 4×10^-2 Ohm-cm with increase in thickness of the films.