On the growth process of Cu2ZnSn(S,Se)(4) absorber layer formed by selenizing Cu-ZnS-SnS precursors and its photovoltaic performance

摘要

Sputtering and subsequent sulfurization (or selenization) is one of the methods that have been extensively employed to fabricate Cu2ZnSn(S,Se)(4) (CZTSSe) thin films. However, there are limited reports on the effect of precursor stacking order of the sputtered source materials on the properties of the synthesized CZTSSe films. In this work, the morphology and crystallization process of the CZTSSe films which were prepared by selenizing Cu-ZnS-SnS precursor layers with different stacking sequences and the adhesion property between the as-synthesized CZTSSe layer and Mo substrate have been thoroughly investigated. It has been found that the growth of CZTSSe material and the morphology of the film strongly depend on the location of Cu layer in the precursor film. The formation of CZTSSe starts from the diffusion of Cu-Se to Sn(S,Se) layer to form Cu-Sn-(S,Se) compound, followed by the reaction with Zn(S,Se). The investigation of the morphology of the CZTSSe films has shown that large grains are formed in the film with the precursor stacking order of Mo/SnS/ZnS/Cu, which is attributed to a bottom-to-top growth mechanism. In contrast, the film made from a precursor with a stacking sequence of Mo/ZnS/SnS/Cu is mainly consisted of small grains due to a top-to-bottom growth mechanism. The best CZTSSe solar cell with energy conversion efficiency of 3.35% has been achieved with the selenized Mo/ZnS/SnS/Cu film, which is attributed to a good contact between the absorber layer and the Mo substrate. (C) 2014 Elsevier B.V. All rights reserved.