Highly Efficient CdTe Thin-Film Solar Cells Fabricated by Pre-Oxidized CdSeTe Sources

Abstract

Selenium alloying into a CdTe thin-film solar cell absorber has been one of the most significant advances in CdTe solar cell fabrication over the last decade. Oxygen plays a critical role in the CdSeTe deposition process, mainly to increase Se concentration in as-deposited CdSeTe films. However, it is hard to fabricate CdSeTe films with controllable Se concentration in a deposition chamber, which is usually filled with a certain atmosphere of O₂. In this work, we propose an alternative technique for Se alloying in CdSeTe films, that is, to pre-oxidize CdSeTe powder sources and then fabricate CdSeTe films in a O₂-free deposition chamber. The oxides formed on the oxidized CdSeTe source surface effectively suppress Te sublimation and hence increase Se concentration in the CdSeTe films. Furthermore, the presence of nonequilibrium, metastable hexagonal CdSeTe phase enhances Se incorporation into the CdTe films. The experimental results presented in this study demonstrate that using pre-oxidized CdSeTe powder source is a promising technique to control Se element in the form of graded distribution in highly efficient CdSeTe/CdTe thin-film solar cells. The highest cell efficiency achieved in this study is 16.4%.