Fabrication of CZTS thin films and solar cells via single-step Co-evaporation method

Despite remarkable enhancements that have been achieved during the past years, the photovoltaic performance of CZTS is far below the theoretical expectation. It appears that the profound breakthrough has to be made internally in the aspect of absorber itself, indicating the significance of fabrication strategies. Therefore, this study adopts the single-step co-evaporation method, which has been proved essentially successful for CIGS, to simultaneously achieve on-site deposition and considerably handy control of the film growth process. On this basis, we demonstrate that ZnS segregation can be alleviated through subtle growth profile modification. According to the evolution of series resistance and the conversion efficiency, the carrier transport blocking behavior which arises from ZnS is distinctly reduced. Furthermore, we achieve substantial control of the Sn-contained volatile phases so that the chemical equilibrium is beneficially shifted and the decomposition of CZTS is suppressed, bringing in significantly improved photovoltaic performance compared to the references. A power conversion efficiency of 4.3% is achieved with a considerable open-circuit voltage of 608 mV. The results in this study validate the potential along with the convenience of the single-step co-evaporation method.