Chemical Incorporation of Copper into Indium Selenide Thin-films for Processing of CuInSe_2 Solar Cells

摘要

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 CuInSe_2 (CIS) layers suitable for solar cell processing. The precursor and converted layers have been investigated with scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). 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 In_2Se_3 and Cu_(2-x)Se. Selenisation of the precursor layer homogenises the composition and forms chalcopyrite CIS. These CIS layers exhibit a dense micro-structure with rough surface morphology, which is ascribed to a non-optimal selenisation process. Solar cells with the structure ZnO: Al/i-ZnO/CdS/CIS/Mo/glass have been processed from the selenised layers and have exhibited efficiencies of up to 4 percent under simulated AM1.5 illumination.