Selenization of Cu2ZnSnS4 thin films obtained by pneumatic spray pyrolysis

•CZTS thin films deposited by pneumatic spray pyrolysis.•Selenization conditions modify the composition, band gap and crystallinity of the films.•High crystallinity CZTSSe solid solution is formed after selenization.•CZTSSe-based solar cells with efficiencies up to 2.1% are reported.

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 Jsc = 21.9 ma/cm2, Voc = 287.7 and F.F. = 33.4%.