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.

► Precursor CZTS films are non-stoichiometric with binary sulfide phases.
► Cu-capping (140 nm) on precursor CZTS provides near stoichiometric films.
► Raman spectroscopy reveals the formation of CZTS phase after Cu-capping.
► Cu-capped CZTS samples show an improved Cu/(Zn + Sn) ratio of ∼0.71.