Formation mechanisms of voids and pin-holes in CuSbS2 thin film synthesized by sulfurizing a co-sputtered Cu–Sb precursor

Abstract

Chalcostibite CuSbS₂ is a promising alternative absorber material for thin film solar cells but the poor photovoltaic device performance limits its wide application. In this work, one of the main loss mechanisms of structural defects such as voids and pin-holes has been investigated systematically via a quasi in situ method. Through studying the formation mechanisms of voids and pin-holes in CuSbS₂ synthesized by sulfurizing a co-sputtered Cu–Sb metallic precursor, it is found that Cu vacancies can be formed and accumulated in preliminary voids as a result of the outward diffusion of Cu atoms during the heating process via the Kirkendall effect. Subsequently, the cracks between newly formed layers and small spaces caused by volume expansion further contributed to the final visible voids. In addition, two possible mechanisms, uneven grain growth of CuSbS₂ and volume shrinkage estimated by the Pilling–Bedworth model, are proposed to explain the formation of pin-holes, paving the way to achieve high efficiency CuSbS₂ solar cells.