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 Cu2ZnSn(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 (Tsub) is increased from 100 to 500°C. The crystal structure of all CZTSSe films are identified to be preferentially (112)-oriented, polycrystalline in nature, and without the existence of secondary phases such as Cu2(S,Se) or Zn(S,Se). The full-width at half-maximum of (112) diffraction peak is the minimum with a value of 0.12° and the maximum crystallite size 75.11nm for CZTSSe grown at 300°C. Morphological investigation reveals the achievement of the largest grain size at Tsub=300°C. The band gap of CZTSSe thin films at room temperature, as determined by spectroscopic ellipsometry, varies from 1.23 to 1.70eV, depending on Tsub. The optical absorption coefficient of all CZTSSe thin films is >104cm−1.