Optimized fabrication of sputter deposited Cu₂ZnSnS₄ (CZTS) thin films

An effective synthesis strategy is employed to fabricate Cu₂ZnSnS₄ (CZTS) thin films using radio frequency (rf) magnetron sputtering technique on soda lime glass substrates. The as-grown films are annealed at different temperatures ranging between 350 and 550°C, and their chemical compositions and structural properties are investigated. The as-grown films have poor Cu/(Zn+Sn) ratios ranging between 0.39 and 0.44 and S/(Cu+Zn+Sn) ratios ranging between 0.97 and 1.21. The Cu/(Zn+Sn) ratio is improved by growing a thin additional Cu-capping layer on the as-grown film followed by annealing. An improved Cu/(Zn+Sn) ratio of ~0.71 is obtained and the S/(Cu+Zn+Sn) ratio is slightly reduced to ~0.85. The formation of a kesterite type CZTS is confirmed using X-ray diffraction and Raman spectroscopy measurements. Absorption measurements and band-gap energy determination of the CZTS films are carried out in order to confirm applicability to solar cells.