Diffusion Coefficients of Selenium and Gallium during the Cu(In1-xGax)Se2 Thin Films Preparation Process

Abstract

Cu (In1-xGax)Se2 (CIGS) polycrystalline thin films with Ga-gradient structures were prepared by selenization of sputtered Cu-In-Ga precursors. The Ga contents of the as-selenized CIGS thin films were measured by EDS. With greater Ga content, the peaks in the diffraction pattern become broadened. Auger electron spectroscopy was used to measure the composition distribution of the Cu, In, Ga, and Se elements in the CIGS and CuInSe2 films. At 300°C, the diffusion coefficients DSe was approximately (6.7±1.0) x 10-16 m2s-1, and DGa was about (4.5±1.0) x 10-18 m2s-1. DSe are two orders of magnitude greater than DGa, which is also the reason why the selected CIGS film was almost completely selenized, but still able to keep certain Ga-grading profile. The temperature used in this work is within the low temperature range of the two-step selenization approach, which is more suitable for low-cost substrates like flexible substrates.