Chemical incorporation of copper into indium selenide thin-films for processing of CuInSe2 solar cells

A chemical method of incorporating copper into indium selenide thin-films has been investigated, with the goal of creating a precursor structure for conversion into CuInSe2 layers suitable for solar cell processing. The precursor and converted layers have been investigated with scanning electron microscopy, x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy. From these measurements, the incorporation of copper into the indium selenide layers is concluded to proceed by an ion-exchange reaction. This reaction results in the formation of a precursor layer with a graded compositional depth-profile containing the crystalline phases In2Se3 and Cu2-xSe. Selenization of the precursor layer homogenises the composition and forms chalcopyrite CuInSe2. These CuInSe2 layers exhibit a dense microstructure with rough surface morphology, which is ascribed to a non-optimal selenization process. Solar cells with the structure ZnO:Al/i-ZnO/CdS/CuInSe2/Mo/Glass have been processed from the selenized layers and have exhibited efficiencies of up to 4% under simulated AM1.5 illumination