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

Cu(In, Ga)Se-2 thin films were deposited on Mo/soda-lime glass substrates by the one-stage co-evaporation process at the substrate temperatures (T-sub) from 350 degrees C to 550 degrees 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 degrees C is critical for CIGS films grown by the one-stage process. The (In, Ga)(2)Se-3 phase with high resistivity is found below this temperature. The higher T-sub 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)(2)Se-3 phase in CIGS films. Additionally, the performance of the CIGS solar cells improves significantly with the increase of T-sub. It can be attributed to the reduction of the grain-boundary recombination and the sufficient reaction between the additional (In, Ga)(2)Se-3 phase and the CuxSey binary phase at T-sub above 500 degrees C.