Effect of substrate temperature on the structural and electrical properties of CIGS films based on the one-stage co-evaporation process

Abstract

Cu(In, Ga)Se2 thin films were deposited on Mo/soda-lime glass substrates by the one-stage co-evaporation process at the substrate temperatures (Tsub) from 350 °C to 550 °C. The structural and electrical properties of CIGS films have been studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) and Hall effect measurement. The experimental results indicate that a temperature of 450 °C is critical for CIGS films grown by the one-stage process. The (In, Ga)2Se3 phase with high resistivity is found below this temperature. The higher Tsub will lead to the formation of single-phase CIGS films with larger grain size and better electrical properties. A higher carrier concentration and lower resistivity of CIGS films are ascribed to sodium incorporation diffused from the glass substrate and the disappearance of the (In, Ga)2Se3 phase in CIGS films. Additionally, the performance of the CIGS solar cells improves significantly with the increase of Tsub. It can be attributed to the reduction of the grain-boundary recombination and the sufficient reaction between the additional (In, Ga)2Se3 phase and the CuxSey binary phase at Tsub above 500 °C.