TiO ₂ Novel Application in CIGS Solar Cell: Se Diffusion Barrier and Interface Modification

A TiO 2 diffusion barrier was introduced at the Mo/CIGS interface to control MoSe 2 formation. The TiO 2 layer exhibits excellent Se‐blocking performance, effectively suppressing Se diffusion at a thickness of merely 40 nm while remaining immune to selenization. However, the significant energy band mismatch between TiO 2 and CIGS adversely affects carrier collection efficiency and degrades device performance. To address this limitation, an additional sacrificial Mo layer was deposited upon TiO 2 to form a TiO 2 /MoSe 2 intermediate bilayer, which promotes proper band alignment at the back interface. Furthermore, the solid solubility of Cu in TiO 2 reduces Cu content in the absorber, generating additional V Cu defects that enhance carrier concentration and built‐in electric field strength, thereby suppressing front interface recombination. Consequently, the implementation of a thickness‐optimized TiO 2 /MoSe 2 intermediate bilayer significantly mitigates carrier recombination and improves device performance.