The effects of In2Se3 wetting layers on Cu(In, Ga)Se2 thin films and devices

Thin films of Cu(In, Ga)Se₂ (CIGS) are grown on substrates coated with thin (10-60 nm) In₂Se₃ wetting layers. The In₂Se₃ changes the surface energy of the substrate, impacting nucleation and grain growth of the CIGS. Films at various stages of growth are evaluated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The March-Dollase approach is applied to quantify the degree of preferred orientation at each stage. Devices are fabricated using full thickness films deposited both with and without wetting layers. The morphology changes markedly in the presence of the wetting layer, even while the degree of preferred orientation and device properties remain relatively unchanged. These results offer one possible explanation for the variation in morphology that is seen in the literature, even while performance characteristics remain relatively constant among various laboratories and deposition methods.