Growth and characterization of high quality CIGS films using novel precursors stacked and surface sulfurization process

Abstract

This study produces high quality Cu(In,Ga)Se2 (CIGS) solar cells using a two-step process. Stacked In (200 nm)/CuGa (150 ~ 300 nm)/In (500 nm) layers are deposited onto Mo bilayer soda-lime glass by sputtering, using CuGa and In targets, followed by vapor stacking of the elemental Se layers. To produce the CIGS film, the CuGa film is coated in thicknesses of 150, 200, 250 and 300 nm. An appropriate atomic ratio [Cu/(In + Ga), CGI and Ga/(In + Ga), GGI] for the precursors and the CIGS absorption layers composition is easily obtained. Compared to those for the as-deposited precursors, after selenization, the CGI and GGI ratios for CIGS films are almost constant. All CIGS thin films exhibit a peak in the Raman curves at around 173–174 cm−1, which is identified as the CIGS phase. Following sulfurization, the main peaks for CIGS thin films at (112), (220)/(204) and (312)/(116) indicated that the crystalline quaility were improved. The main peaks for the CIGSS films are slightly greater for (112), (220)/(204) and (312)/(116). The band gap energy is increased from 1.19 eV (for the as-grown) to 1.34 eV (for the absorber layer that is sulfurized at 500 °C for 10 min). The performance of the CIGS absorber films is improved by using a proper holding time for sulfurization.