Separation of Tellurium from Various Tellurides Relevant for Photovoltaics and from Pre-product Thin Film Solar Cells for Recycling by Chemical Vapor Transport

Abstract

Thin-film solar cells based on CdTe are a viable technology for renewable energy generation due to their low production cost and relatively easy manufacturing. However, the scarcity and toxicity of Te necessitates the recovery of this element from end-of-life solar cells. In addition to CdTe, these solar cells contain several other tellurides, including Cu₂Te, ZnTe and SnTe. In this study, chemical vapor transport (CVT), using sulfur as a transport agent (TA), was utilised as an energy-efficient and waste-minimal method to separate Te from all the aforementioned tellurides in both open and closed systems. While transport rates of Te were demonstrated to be low in a closed system for CdTe and ZnTe, CVT in an open system can accelerate the procedure strongly, reaching recovery rates of 56 % h^-1 and 47 % h^-1 for CdTe and ZnTe resprectively. The Te recovery rate for SnTe was 32 % h^-1, which was eighty times higher for the open system than in a closed system at moderate T = 425 °C. For Cu₂Te, the open system even enabled Te transport that was not possible in the closed system. The feasibility of the CVT for recycling was further demonstrated by the use of pre-product thin film solar cells. In-situ experiments utilizing a transport balance comparing CVT of Te starting from elemental Te and from CdTe or ZnTe revealed that the redox reaction does not seriously slow down the process.