Na-induced effects on the electronic structure and composition of Cu(In,Ga)Se2 thin-film surfaces

Abstract

X‐ray and UV photoelectron spectroscopy measurements of Cu(InGa)Se₂ thin films grown on Mo coated soda‐lime glass show segregation from the substrate and formation of two different Na species. One of these species is also identified after deliberate deposition of metallic Na. Moreover, the adsorption (or segregation) of this species reduces the native oxide SeO₂, while the other, reacted Na species coexists with SeO₂. Small amounts of Na (≤0.05 Å) induce a band bending and reduce the surface dipole. These findings reveal a positive influence of segregated Na on the morphology and electrical characteristics of Na‐enriched films, improving the overall performance of the solar cells.