The electrical and structural characteristics of CIGS thin films prepared by sol-gel method

Low cost sol-gel method to prepare CIGS thin films is studied in this paper. The influence of Cu/III and Ga/III composition ratio on the characteristics of CIGS film has been investigated. It is found that the Cu/III composition ratio of 1.3 in the sol-gel solution can obtain a good stoichiometric CIGS film. The reduction temperature of lower than 300 °C is better to effectively remove residual oxygen. The selenization temperature is about 500-520 °C to obtain a good quality of CIGS films. The XRD spectra indicate that the CIGS thin films exhibit a chalcopyrite structure. The main chalcopyrite structure peak of (112) will shift to higher angle when the gallium content is higher in the CIGS absorber layer. Raman microscope can easily identify the Cu₂Se phase in CIGS films. In addition, Raman peak will shift with the addition of gallium in CIGS films. The CIGS absorber layer has the band gap between 1.01 eV to 1.65 eV with the various gallium contents. The carrier concentration, mobility and resistivity of the CIGS films are about 10¹⁵-10¹⁶ cm^-3, 17-22 cm²/v·s and 10² Ω-cm, respectively. It is within an acceptable range for making a high efficiency CIGS solar cell.