Suppressing the formation of an interfacial MoSe2 layer in Cu2ZnSnSSe4 thin film solar cells: 8.0% power conversion efficiency with an ultrathin carbon-based diffusion barrier
Yi-Rung Lin1,2,4,5*, Wei-Chao Chen3,4,5, Meng-Chia Hsieh4,5,6, Tsu-Chin Chou4,5, Shao-Sian Li7, Cheng-Ying Chen4,5, Ling-Kang Liu1,8, Chun-Wei Chen7, Li-Chyong Chen5, Kuei-Hsien Chen4,5
1Department of Chemistry, National Taiwan University, Taipei, Taiwan
2Nano Science and Technology Program,Taiwan International Graduate Program, Academia Sinica and National Taiwan University, Taiwan
3Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan
4Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
5Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
6Institute of Organic and Polymeric Materials, National Taipei University of Technology, Taipei, Taiwan
7Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan
8Institute of Chemistry, Academia Sinica, Taipei, Taiwan
* presenting author:Yi-Rung Lin,
The importance of the back contact modification has attracted considerable attention for improving power conversion efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this study, we utilized an ultrathin diffusion barrier to suppress the formation of MoSe2 layer. The ultrathin layer, which was made by carbon-based materials, functions as an effective Se diffusion barrier during a high-temperature selenization process. The material properties of the diffusion barrier and the device performance were both comprehensively investigated. By introducing the diffusion barrier, the MoSe2 layer could effectively suppress the formation of MoSe2 layer during high-temperature selenization process from 300 nm to 150 nm, which is about 50% decrease in thickness. Thus, the series resistance of CZTSSe solar cells was reduced to a low level (≈2.3 Ω cm2 ). Besides, the carrier dynamics and defect-level properties of CZTSSe solar cells were also shown largely enhancement because of the reduced MoSe2 layer, which would cause carrier recombination. As a consequence, the device performance of CZTSSe solar cells is improved significantly. A champion CZTSSe solar cell with efficiency of 8.0% is fabricated.

Keywords: diffusion barrier, carbon-based, CZTS solar cells, carrier dynamics, defect level energy