Mechanism analysis of CuInS2 and Cu(In,Ga)S2 growth via KCN- and H2S-free process and solar-cell application

In this article, CuInS2 (CIS) and Cu(In,Ga)S-2 (CIGS) absorbers are prepared via sulfurization by a sulfur powder source for co-evaporated Cu-In(-Ga) metal precursors without toxic KCN and H2S. The CIS and CIGS growth mechanism during sulfurization and their application to solar cells are discussed. X-ray diffraction and Raman spectroscopy analyses indicate that CuS and (In,Ga)(2)S-3 exist at the frontside and the backside, respectively, in the CIGS films at the temperature between 250 degrees C and 350 degrees C. Then, these intermediate phases react at 400 degrees C or higher forming CIGS. Finally, CIS and CIGS solar cells with efficiencies of 3.7% and 7.2% are achieved, utilizing an optimum temperature of 600 degrees C.