Synthesis of CIGS absorber layers from bilayer metal precursors

In-situ X-ray diffraction was used to study the pathways and kinetics as well as the Ga distribution during selenization of CIGS absorbers. Specifically a bilayer metal precursor structure consisting of a Cu-In bottom layer and a Cu-Ga top layer was examined. Precursor films were deposited on Mo-coated thin glass substrates using a molecular beam epitaxial reactor. During selenization of the precursor films, the only selenide observed was CuSe and CIGS. The compounds CuIn and Cu₁₁In₉ and the solid solution CuIn_xGa_1-x, were evident. Notably, CGS did not form during temperature ramp selenization. Isothermal experiments were carried out and data were reduced using Avrami solid-state growth model to yield activation energy values for the formation of CIGS of 76 (±14) and 107 (±15) kJ/mol without and with a Se cap, respectively. The samples were further analyzed by TEM-EDS to measure the Ga distribution as well as by SEM (microstructure) and ICP (final composition).