Growth and characterization of dual ion beam sputtered Cu2ZnSn(S, Se)4 thin films for cost-effective photovoltaic application

Abstract A systematic growth optimization of Cu 2 ZnSn(S, Se) 4 (CZTSSe) thin films by dual ion beam sputtering system from a single CZTSSe target is presented. It is observed that the ratio of Cu/(Zn + Sn) varies from 0.86 to 1.5 and that of (S + Se)/metal varies between 0.62 and 0.97 when substrate temperature (T sub ) is increased from 100 to 500 °C. The crystal structure of all CZTSSe films are identified to be preferentially (1 1 2)-oriented, polycrystalline in nature, and without the existence of secondary phases such as Cu 2 (S, Se) or Zn(S, Se). The full-width at half-maximum of (1 1 2) diffraction peak is the minimum with a value of 0.12° and the maximum crystallite size 75.11 nm for CZTSSe grown at 300 °C. Morphological investigation reveals the achievement of the largest grain size at T sub  = 300 °C. The band gap of CZTSSe thin films at room temperature, as determined by spectroscopic ellipsometry, varies from 1.23 to 1.70 eV, depending on T sub . The optical absorption coefficient of all CZTSSe thin films is >10 4  cm −1 .