Investigations on the growth of Cu2ZnSnS4 thin films for solar cell absorber layer

Cu2ZnSnS4 (CZTS), a quaternary semiconductor of kesterite family, is a potential candidate for absorber layer in thin film heterojunction solar cells. Cu2ZnSnS4 films have been deposited by spray pyrolysis technique onto chemically cleaned soda-lime glass substrates held at an optimized substrate temperature (Ts) of 633 K. The effect of deposition time on the growth of CZTS films deposited at the optimized substrate temperature is investigated. Powder XRD studies revealed that, the films deposited in the first 2-4 min are mostly amorphous in nature. On further increase in deposition time, the crystallinity is increased. CZTS thin films with (112) preferred orientation of kesterite could be obtained when the deposition time is 8 min. The lattice parameters are found to be a = 0.543 nm and c = 1.085 nm. The optical band gap and absorption coefficient (α) of these films were found to be 1.5 eV and >104 cm−1 respectively. The films are found to be p-type in nature. An attempt is made for fabrication of CZTS solar cell entirely by chemical approach. Spray pyrolyzed CZTS as absorber layer, chemical bath deposited CdS as buffer layer, spray pyrolyzed ZnO:Al as TCO layer, exhibited an open circuit voltage of 140 mV and short circuit current density of 0.8 mA/cm2.