Effects of Sb-doping on the grain growth of Cu(In, Ga)Se₂ thin films fabricated by means of single-target sputtering

To investigate the effects of Sb doping on the kinetics of grain growth in Cu(In,Ga)Se₂ (CIGS) thin films during annealing, CIGS thin films were sputtered onto Mo coated substrates from a single CIGS alloy target, followed by chemical bath deposition of Sb₂S₃ thin layers on top of CIGS layers and subsequent annealing at different temperatures for 30 min in Se vapors. X-ray diffraction results showed that CIGS thin films were obtained directly using the single-target sputtering method. After annealing, the In/Ga ratio in Sb-doped CIGS thin films remained stable compared to undoped film, possibly because Sb can promote the incorporation of Ga into CIGS. The grain growth in CIGS thin films was enhanced after Sb doping, exhibiting significantly larger grains after annealing at 400 C or 450 C compared to films without Sb. In particular, the effect was strikingly significant in grain growth across the film thickness, resulting in columnar grain structure in Sb-doped films. This grain growth improvement may be led by the diffusion of Sb from the front surface to the CIGS-Mo back interface, which promoted the mass transport process in CIGS thin films.