Selenization of Cu₂ZnSnS₄ thin films obtained by pneumatic spray pyrolysis

Cu₂ZnSnS₄ thin films have been deposited by pneumatic spray pyrolysis technique under Argon atmosphere followed by a selenization step to induce film crystallization. This study deals with two different annealing parameters: the variation of annealing temperature in the range of 450 °C–580 °C and the variation of elemental Se weight available for annealing. With these two parameters it is possible to obtain films with a systematic reduction of the optical band gap energy as the composition of the films shifts from S-pure towards Se-rich as confirmed by Raman and X-ray diffraction. Pulsed glow discharge spectrometry was used to disclose the in-depth compositional profiles of the films; finding that the films results to be Se-rich but not S-free. Solar cells were processed with efficiencies up to 2.1%, with J_sc = 21.9 ma/cm², V_oc = 287.7 and F.F. = 33.4%.