Synergetic Effects of Zn Alloying and Defect Engineering on Improving the CdS Buffer Layer of Cu2ZnSnS4 Solar Cells

Liangli Chu; Jinping Zhang; Huiwen Xiang; Sixin Wu; Yu Jia; Chengyan Liu

doi:10.1021/acs.inorgchem.2c01575

Synergetic Effects of Zn Alloying and Defect Engineering on Improving the CdS Buffer Layer of Cu₂ZnSnS₄ Solar Cells

Inorg Chem. 2022 Aug 8;61(31):12293-12300. doi: 10.1021/acs.inorgchem.2c01575. Epub 2022 Jul 27.

Authors

Liangli Chu¹, Jinping Zhang², Huiwen Xiang¹, Sixin Wu¹, Yu Jia¹, Chengyan Liu¹

Affiliations

¹ Henan Key Laboratory of Photovoltaic Materials, Key Laboratory for Special Functional Materials of Ministry of Education, and The Joint Center for Theoretical Physics, Henan University, Kaifeng 475004, People's Republic of China.
² Faculty of Engineering, Huanghe Science and Technology College, Zhengzhou 450006, People's Republic of China.

PMID: 35894558
DOI: 10.1021/acs.inorgchem.2c01575

Abstract

The inferior electrical properties at the interface of the Cu₂ZnSnS₄/CdS (CZTS/CdS) heterojunction resulting in the severe loss of open-circuit voltage (V_oc) highly restrict the photovoltaic efficiency of CZTS solar cell devices. Here, first-principles calculations show that the Zn-alloyed CdS buffer layer reverses the unfavorable cliff-like conduction band offset (CBO) of CZTS/CdS to the desirable spike-like CBO of CZTS/Zn_0.25Cd_0.75S, which suppresses carrier nonradiative recombination and blocks electron backflow. In addition, the weakened n-type conductivity of Zn_0.25Cd_0.75S can be enhanced by In, Ga, and Cl doping without the introduction of detrimental deep-level defects and severe band-tail states, which improves the V_oc of CZTS solar cells by promoting strong band bending and large quasi-Fermi-level splitting at the absorber side of the CZTS/Zn_0.25Cd_0.75S heterojunction. This study finds that the synergetic effects of Zn alloying and defect engineering on the CdS buffer layer are promising for overcoming the long-standing issue of the V_oc deficit in CZTS solar cells, and understanding the optimized interfacial electrical properties provides theoretical guidance for improving the efficiency of semiconductor devices.