Suppressing Element Inhomogeneity Enables 14.9% Efficiency CZTSSe Solar Cells

• Published in: Advanced materials (Weinheim) 2024-06, Vol.36 (25), p.e2400138-n/a
• Main Authors: Li, Yimeng, Cui, Changcheng, Wei, Hao, Shao, Zhipeng, Wu, Zucheng, Zhang, Shu, Wang, Xiao, Pang, Shuping, Cui, Guanglei
• Format: Article
• Language: English
• Subjects: Copper; Crystal defects; Cu‐directional diffusion; CZTSSe solar cell; Diffusion barriers; Diffusion layers; Efficiency; Inhomogeneity; Photovoltaic cells; Selenium; Solar cells; Tin; VOC loss
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202400138

Kesterites, Cu2ZnSn(SxSe1−x)4 (CZTSSe), solar cells suffer from severe open‐circuit voltage (VOC) loss due to the numerous secondary phases and defects. The prevailing notion attributes this issue to Sn‐loss during the selenization. However, this work unveils that, instead of Sn‐loss, elemental inhomogeneity caused by Cu‐directional diffusion toward Mo(S,Se)2 layer is the critical factor in the formation of secondary phases and defects. This diffusion decreases the Cu/(Zn+Sn) ratio to 53% at the bottom fine‐grain layer, increasing the Sn‐/Zn‐related bulk defects. By suppressing the Cu‐directional diffusion with a blocking layer, the crystal quality is effectively improved and the defect density is reduced, leading to a remarkable photovoltaic coversion efficiency (PCE) of 14.9% with a VOC of 576 mV and a certified efficiency of 14.6%. The findings provide insights into element inhomogeneity, holding significant potential to advance the development of CZTSSe solar cells. Elemental inhomogeneity caused by Cu‐directional diffusion toward Mo(S,Se)2 layer is demonstrated to be the critical factor in the formation of secondary phases and defects. By suppressing the Cu‐directional diffusion with a blocking layer, a remarkable efficiency of 14.9% is achieved, with an open‐circuit voltage (VOC) of 576 mV and a certified efficiency of 14.6%.