Voids in kesterites and the influence of lamellae preparation by focused ion beam for transmission electron microscopy analyses

Abstract

Kesterite solar cells based in Cu2ZnSnS4 and Cu2ZnSnSe4 are potential future candidates to be used in thin film solar cells. The technology still has to be developed to a great extent and for this to happen, high levels of confidence in the characterization methods are required so that improvements can be made on solid interpretations. In this study we show that the interpretations of one of the most used characterization techniques in kesterites, scanning transmission electron microscopy (STEM), might be affected by its specimen preparation when using focused ion beam (FIB). Using complementary measurements based on scanning electron microscopy and Raman scattering spectroscopy, compelling evidences show that secondary phases of ZnSe mixed in the bulk of Cu2ZnSnSe4 are the likely cause of the appearance of voids in the STEM lamellae. Sputtering simulations support this interpretation by showing that Zn in a ZnSe matrix is preferentially sputtered compared with any metal atom in a Cu2ZnSnSe4 matrix.