An investigation of Na-related defects in Cu2ZnSnSe4

Abstract

Using hybrid density functional theory, here, we have investigated the electronic, defect and migration properties of Na-related defects in the earth-abundant solar cell absorber material Cu₂ZnSnSe₄ (CZTSe). We find that among all the Na-related defects, Na_Zn acts the same way as V_Cu and Cu_Zn; it is an acceptor and contributes to the p-type conductivity. Na_Sn is a deep level defect, but it is energetically unfavorable and can be suppressed by the growth conditions. Besides, through migration energy analysis, we prove that Na can easily move in CZTSe through interstitial Na and Cu vacancy mediated mechanisms.