Preparation of Cu(In,Ga)Se₂ thin films at low substrate temperatures

Cu(In,Ga)Se₂(CIGS) thin films were prepared at substrate temperatures of 350 to 500 °C. The (In,Ga)₂Se₂ precursor layers were deposited on Mo coated soda-lime glass and then exposed to Cu and Se fluxes to form CIGS films. The surface composition was probed by a real-time composition monitoring method. The CIGS films were characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, secondary ion mass spectroscopy, and atomic force microscopy. The transient formation of a Cu–Se phase with a high thermal emissivity was observed during the deposition of Cu and Se at a substrate temperature of 350 °C. Faster diffusion of In than Ga from the (In,Ga)₂Se₃ precursor to the newly formed CIGS layer was observed. A growth model for CIGS films during the deposition of Cu and Se onto (In,Ga)₂Se₃ precursor is proposed. A solar cell using a CIGS film prepared at about 350 °C showed an efficiency of 12.4%.