Get access

Classification of Lattice Defects in the Kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 Earth-Abundant Solar Cell Absorbers

Authors

  • Shiyou Chen,

    Corresponding author
    1. Key Laboratory of Polar Materials and Devices (MOE), East China Normal University, Shanghai 200241, China
    2. Key Laboratory for Computational Physical Sciences (MOE), Surface Physics Laboratory, Fudan University, Shanghai 200433, China
    • Key Laboratory of Polar Materials and Devices (MOE), East China Normal University, Shanghai 200241, China
    Search for more papers by this author
  • Aron Walsh,

    1. Center for Sustainable Chemical Technologies, Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK
    Search for more papers by this author
  • Xin-Gao Gong,

    1. Key Laboratory for Computational Physical Sciences (MOE), Surface Physics Laboratory, Fudan University, Shanghai 200433, China
    Search for more papers by this author
  • Su-Huai Wei

    Corresponding author
    1. National Renewable Energy Laboratory, Golden, CO 80401, USA
    • National Renewable Energy Laboratory, Golden, CO 80401, USA.
    Search for more papers by this author

Abstract

The kesterite-structured semiconductors Cu2ZnSnS4 and Cu2ZnSnSe4 are drawing considerable attention recently as the active layers in earth-abundant low-cost thin-film solar cells. The additional number of elements in these quaternary compounds, relative to binary and ternary semiconductors, results in increased flexibility in the material properties. Conversely, a large variety of intrinsic lattice defects can also be formed, which have important influence on their optical and electrical properties, and hence their photovoltaic performance. Experimental identification of these defects is currently limited due to poor sample quality. Here recent theoretical research on defect formation and ionization in kesterite materials is reviewed based on new systematic calculations, and compared with the better studied chalcopyrite materials CuGaSe2 and CuInSe2. Four features are revealed and highlighted: (i) the strong phase-competition between the kesterites and the coexisting secondary compounds; (ii) the intrinsic p-type conductivity determined by the high population of acceptor CuZn antisites and Cu vacancies, and their dependence on the Cu/(Zn+Sn) and Zn/Sn ratio; (iii) the role of charge-compensated defect clusters such as [2CuZn+SnZn], [VCu+ZnCu] and [ZnSn+2ZnCu] and their contribution to non-stoichiometry; (iv) the electron-trapping effect of the abundant [2CuZn+SnZn] clusters, especially in Cu2ZnSnS4. The calculated properties explain the experimental observation that Cu poor and Zn rich conditions (Cu/(Zn+Sn) ≈ 0.8 and Zn/Sn ≈ 1.2) result in the highest solar cell efficiency, as well as suggesting an efficiency limitation in Cu2ZnSn(S,Se)4 cells when the S composition is high.

Get access to the full text of this article

Ancillary