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Abstract:
We have performed density functional theory calculations using the HSE06
hybrid functional to investigate the energetics, atomic, and electronic
structure of intrinsic defects as well as Na and K impurities in the
kesterite structure of the Cu2ZnSnSe4 (CZTSe) solar cell material. We
found that both Na and K atoms prefer to be incorporated into this
material as substitutional defects in the Cu sublattice. At this site
highly stable (Na-Na), (K-K), and (Na-K) dumbbells can form. While Na
interstitial defects are stable in CZTSe, the formation of K
interstitial defects is unlikely. In general, the calculated formation
energies for Na-related defects are always lower compared to their
K-related counterparts. On the basis of thermodynamic charge transition
level calculations, we can conclude that the external defects are
harmless except Na-sn and K-sn. These defects induce gap states that
might be detrimental for the device performance.
