Pure Sulfide Kesterite Solar Cell via Solution Processing

The performance of pure sulfide kesterite Cu₂ZnSnS₄ (CZTS) solar cell is limited by severe open circuit voltage deficit due to the carrier recombination in absorber bulk and at interfaces caused by high concentration of defects and unfavorable energy band alignment at heterojunction interface. Here, we report fabrication of CZTS solar on FTO substrates from dimethyl sulfoxide based molecular solution and mitigating the above issue by alkali ion doping and metal ion alloying. We have first adjusted the stoichiometric ratio in the precursor solution and introduced Na to suppress the formation of the deleterious secondary phases in the CZTS absorber films, achieving an efficiency of 8.36%. Second, Cd alloying was performed to improve film crystallinity, decrease the defect density, and lower energy levels of VBM and CBM, which reduces carrier recombination and convert Cliff-type to favorable Spike-type energy band alignment, greatly improving device performance. Further Ag alloying was introduced to eliminate near-horizontal grain boundaries and passivate defects in the bulk-phase and heterojunction interface, resulting in an optimal device photovoltaic conversion efficiency of 10.3% with Cd-Ag co-alloying, the highest-efficiency pure sulfide CZTS solar cell on FTO electrodes. Additionally, the grain growth mechanisms of CZTS have been systematically investigated to understand the origin of the large Voc deficit issue, providing new insights for further mitigating the defect property of this materials.

References:
1. H. Liu, Y. Li, A. Xu, X. Li, C. Xiang, S. Zhou, S. Wang*, W. Yan* and H. Xin*, Solar RRL. 2024, 2400588.
2. A. Xu, X. Li, H. Liu, C. Xiang, C. Ma, Y. Li, X. Pan, W. Yan, S. Wang*, W. Huang* and H. Xin*, Small. 2024, accepted.