Electrosprayed Cu2ZnSnS4 films from its nanoparticles for dye-sensitized solar cells

In this study, nanoparticles of Cu2ZnSnS4 (CZTS) were synthesized by thermal injection method, and then electrospray (ES) method was used to prepare CZTS films, which were applied as counter electrode (CE) in dye-sensitized solar cell (DSSC) devices. The reaction for CZTS powder was complete after 3 h and the crystallinity increases with reaction time. However, CZTS powder with too large grain/particle sizes was difficult to be dispersed in solvent for ES processing. Our CZTS films contains pores, and the film morphology, semiconductor property and electrochemical catalytic activities were influenced by annealing temperature, which influences crystalline states of the film. Higher temperature-annealing is good for crystalline-state development, but for DSSC application, there is trade-off between the crystalline and pore dispersion; and the CZTS film undergoing 450 °C annealing was found to exhibit the best catalytic ability and hence the best DSSC device performance. It was found that compared to CZTS, Pt possesses better catalytic ability, which was found due to the higher charge transfer efficiency between Pt and the redox; but on the other hand, charge transport of our CZTS films and the redox diffusion with CZTS CE are better compared to those of Pt. Under AM 1.5G illumination (100 mW cm−2), DSSC device based on 1 μm CZTS film sintered at 450 °C exhibited a JSC of 22.23 mA cm−2, a VOC of 0.79 V, and a PCE of 8.18%, which is comparable to Pt control-device. In addition, it was supposed that in our CZTS device, both the dye N719 and CZTS contribute to photovoltaic effect.