Control of Point Defects in the Cu(In,Ga)Se-2 Film Synthesized at Low Temperature from a Cu/In2Se3 Stacked Precursor

Abstract

Low-temperature fabrication of Cu(In,Ga)Se-2 (CIGS) film is essential for flexible CIGS solar cells. A large-grained CIGS film was synthesized with a Se-deficient Cu/In,Ga)(2)Se-3 stacked precursor by reacting at 500 degrees C in a vacuum and was then subsequently annealing in Se environment. The CIGS solar cell with the as-prepared CIGS film had a poor cell performance due to a very low Ga composition at the CIGS surface. The surface Ga composition was controlled to 0.2 by supplying In, Ga, and Se in a temperature range of 350 to 500 degrees C. From an analysis of the photoluminescence spectra, we found that the point defects, Se vacancy and In-in-Cu antisite, in the CIGS film were greatly reduced by annealing below 450 degrees C. The short-circuit current was pronouncedly increased in the CIGS cells. The open-circuit voltage depended on both the Ga composition and Cu composition at the CIGS surface. In particular, a low Cu composition at the CIGS surface was essential for the higher performance solar cells. Our results indicated that CIGSs film synthesized at high temperature must be annealed at 350 degrees C or below to reduce undesirable point defects