Sulfurization temperature effects on crystallization and performance of superstrate CZTS solar cells

Kesterite based on Cu2ZnSnS4 composition are considered as promising absorber material for the next generation of photovoltaics due to raw materials abundance and low toxicity. Developing a superstrate architecture using kesterite as an absorber could be the key to a better performance, which allows new ways of engineering the formation of a kesterite thin film. In this work, we study the effects of the sulfurization temperature on the crystallization of kesterite film when is fabricated in a superstrate architecture, and how this affects the performance of a solar cell. We noted that the temperature affects the final composition of the absorber due to cadmium diffusion at 500 ºC from the CdS layer, while the temperature above 530 ºC is essential for a complete Zn incorporation into the crystal structure. The crystallinity is highly affected, and a temperature of 550 ºC is found to be favorable for the crystal growth, and the fabricated device gave improved performance. Impedance spectroscopy measurements suggest the performance enhancement is due to the reduction of defects and an increase of the depletion width in the p-n junction.