Analysis of lattice site occupancy in kesterite structure of Cu2ZnSnS4 films using synchrotron radiation x-ray diffraction

Abstract

The relationship between the composition and the kesterite crystal structure of Cu2ZnSnS4 (CZTS) thin films was investigated. CZTS thin films with three different compositions were produced by sulfurizing the precursors in 5 vol. % H2S balanced with N2. We measured the x-ray diffraction patterns of the CZTS powders scraped away from the CZTS thin films using the synchrotron radiation. The site occupancy of the CZTS thin films that had respectively different compositions were determined by the Rietveld analysis using x-ray powder diffraction patterns. Zn substitutes for Cu at the 2a site with decreasing the value of composition ratio Cu/(Zn+Sn). Meanwhile, Cu substitutes for Sn at the 2b site with increasing the value of Cu/(Zn+Sn). The CZTS thin film with Cu/(Zn+Sn) = 0.8 especially shows a marked tendency that Cu substitutes for Zn at the 2d site and/or Zn substitutes for Cu at the 2c site compared to the CZTS thin films with Cu/(Zn+Sn) = 1.0 and 1.2. We suppose that it is very important to realize the high performance of the photovoltaic generation that CZTS thin films have kesterite crystal structure substituted for Zn at the 2d by Cu and/or substituted for Cu at the 2c site by Zn.