Influence of H2S on the growth of sputter deposited Cu2ZnSnS4 thin film

Abstract

Cu2ZnSnS4 (CZTS) is considered as a suitable absorber layer for thin film solar cells. In the present study, the effect of flow rates of H2S on the fabrication of CZTS thin films are studied in detail. RF magnetron sputtering in the presence of Ar and H2S gas was adopted to deposit sulphides of Cu, Sn and Zn, followed by annealing at higher temperature in H2S ambience in the same chamber to complete the crystallization process. Raman spectra showed peaks corresponding to kesterite CZTS and new impurity peaks observed while the H2S flow rate increases. XRD result helped to identify various secondary phases present along with CZTS phase. It was revealed by FESEM images that the samples prepared at different H2S flow rates exhibiting different nano shapes. Compositional study indicated that the Zn/Sn ratio decreases with H2S flow rate. Surface roughness was calculated by AFM technique and big sulphur aggregates were present on the surface of the sample prepared at high H2S flow rate. Optical bandgap value of the CZTS films was varied from 1.28 to 1.74 eV and electrical parameters were calculated for samples prepared at lower H2S flow rate. This study presents the importance of choosing appropriate H2S flow rates for the fabrication of CZTS thin films.