Obtaining phase-pure CZTS thin films by annealing vacuum evaporated CuS/SnS/ZnS stack

Publication date: 1 July 2016
Source:Journal of Crystal Growth, Volume 445
Author(s): T.G. Sánchez, X. Mathew, N.R. Mathews
Cu2ZnSnS4 (CZTS) thin films were obtained by the sequential thermal evaporation of metal binary sulfides in the order CuS/SnS/ZnS, followed by annealing in Ar/S atmosphere. The as-grown films were annealed at different temperatures ranging between 350 and 600°C, for 10min. Based on the preliminary results, the temperatures 550°C and 600°C were selected for further optimization and a second batch of films were annealed for different time durations (10min, 30min and 60min) at these temperatures in order to identify the conditions to obtain phase-pure CZTS films. The structural properties and chemical compositions at each temperature were investigated in order to optimize the phase purity and film stoichiometry. We have identified adequate and reproducible conditions to obtain the elemental ratio Cu/(Zn+Sn) and Zn/Sn close to 0.78 and 1.19 respectively, which is in the range of material composition required for promising solar cells. In addition the optimized material showed excellent optical and electrical properties to be used as a photovoltaic absorber layer. The optical band gap was found to be about 1.52eV, and the carrier concentration, hall mobility, and resistivity were in the range of 8.372×10¹⁵cm⁻³, 3.103cm²/Vs and 340.3Ω-cm respectively. Three traps with activation energies 4.39, 8.1, and 34meV were detected.



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