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%.