Effect of post-annealing atmosphere on the grain-size and surface morphological properties of pulsed laser deposited CZTS thin films

The Cu2ZnSnS4 (CZTS) thin films have been pulsed laser deposited onto Mo coated glass substrate. The CZTS thin films are of potential importance as an absorber material in solar cells as long as one can optimize the annealing process to enhance their light capturing properties. The aim of the present study is to find the effect of annealing atmospheres such as Ar, N2, N2+H2S gas and S powder on the structural, surface morphological, compositional, optical and electrical properties of CZTS thin films. The structural studies revealed that the as-deposited film was amorphous, but after annealing in different atmospheres at 550 °C, a relatively more intense and sharper diffraction peaks (112), (200), (220), and (312) of kesterites crystal structure with uniform and densely packed surface morphology were observed. It is observed that, the average grain size of the crystallized films depends on the annealing atmosphere. The annealing atmosphere was found to improve the chemical composition of the samples and increase the grain size. The diffusion of sulfur in the film during the annealing process enhanced the crystallinity of the film. Finally, the effect of post-annealing atmosphere on electrical properties of CZTS is also studied.