Effect of substrate temperature on sputtered molybdenum film as a back contact for Cu(In,Ga)Se2 solar cells

Molybdenum (Mo) coated soda lime glass (SLG) is a commonly used substrate for Cu(In,Ga)Se2 (CIGS) solar cells as it also acts as the sodium (Na) source, which improves the efficiency of these devices. In this study, Mo thin films were deposited on SLG substrates using direct-current (DC) magnetron sputtering to observe the influence of substrate temperature on Na diffusion and films smoothness. The working gas (Ar) was maintained at 10 mTorr while substrate temperature was varied from room temperature (RT) to 200° C. In this study, Mo films were characterized using X-Ray Diffraction (XRD). Real time in-situ and ex-situ measurements by spectroscopic ellipsometry were also performed, allowing for the analysis of the growth processes as a function of temperature. Secondary ion mass spectroscopy (SIMS) analysis was carried out to obtain the Na depth profile in the Mo films. In addition, a grain boundary diffusion model was developed to reveal the Na diffusion mechanism in Mo films at various substrate temperatures.