Properties of Cu-doped CdS/CdTe sintered solar cells and $CuInSe_2$ thin films fabricated by sputter-selenization process

Abstract

This thesis consists of two main parts containing Part I., "Effects of Fabrication Conditions on the Properties of $CuInSe_2$ Thin Films", and Part II, "Photovoltaic Properties of Sintered CdS/CdTe Solar cells Doped with Cu". In the Part I, $CuInSe_2$ films were fabricated by two-stage process and the electrical and structural properties of $CuInSe_2$ films were investigated. The Cu-In metal layers were deposited by r.f. sputtering and the selenization of the layers was carried out in hallogen lamp heated tube-furnace, using Se vapor as a source of Se istead of $H_2Se$ gas. In order to increase the grain size of $CuInSe_2$ thin film, two-step heat treatment during selenizing Cu-In metal layer was developed. Two step heat treatment consists of the first step, $450\,^\circ\!C$ for 1 hr, and the second step, $500\sim570\,^\circ\!C$ each for 10 min. The first step was used for the formation of $CuInSe_2$ thin film and the second step for the grain growth of the film. To investigate the effect of selenizing atmosphere on the properties of $CuInSe_2$ thin films, the selenizing atmosphere was varied by introducing $H_2$ gas into (nitrogen+Se vapor). $CuInSe_2$ thin films have been prepared by selenizing three different metal films consisting of Cu/In/substrate and Cu/In/Cu/In/Cu/substrate alloy films deposited by r.f. sputtering. The deposition sequence of Cu-In alloy film affects the surface morphology and the degree of Cu-In alloy mixing of the metal film. Through the two-step heat treatment, the grain size of $CuInSe_2$ thin films increases significantly, the $CuInSe_2$ thin films fabricated by only one-step selenization at $450\,^\circ\!C$ for 1hr have the grain size of far below $1 \mu m$, but those by two-step selenization have much larger grain size than $1 \mu m$. As the second step temperature increases, the grain size of the $CuInSe_2$ thin film increases. During selenization through two-step heat treatment, there is no change in crystallographic orientation...