Effect of Annealing on Physical Properties of Cu2ZnSnS4 (CZTS) Thin Films for Solar Cell Applications

Cu2ZnSnS4 (CZTS) thin films were prepared by directly sputtering Cu (In,Ga)Se2 quaternary target consisting of (Cu: 25%, Zn: 12.5%, Sn; 12.5% and S: 50%). The composition and structure of CZTS layers have been investigated after annealing at 200 0C, 350 0C and 500 0C under vacuum. The results show that recrystallization of the CZTS thin film occurs and increasing the grain size with a preferred orientation in the (112) direction was obtained. The Raman spectra showed the existence of crystalline CZTS phase after annealing. Optical transmission spectra were recorded within the range 300-900 nm. The energy band gap (Eg) of the CZTS thin films was calculated before and after annealing from the transmittance spectra using Beer-Lambert’s law. Results show that Eg is dependent on the annealing temperature. The optical band gap of CZTS also varied from 1.57 eV to 1.31 eV with increase in the annealing temperature from 200 0C min to 500 0C.