Passivation principle of deep-level defects: a study of SnZn defects in kesterites for high-efficient solar cells

Abstract

Deep-levels and band-tail states caused by defects are severely detrimental to the optoelectronic properties of solar cells, however their passivation is challenging. Herein, a general passivation principle for point defects is proposed, which requires that the strong orbital coupling and the octet electron counting rule should be satisfied at defect site. Based on this principle, the longstanding issue of how to passivate the Sn_Zn defects in kesterite could be solved. We find that group VA elements P (As) substituting anions in kesterites can entirely passivate the deep-level of Sn_Zn defect by forming the 2P_S + Sn_Zn (2As_Se + Sn_Zn) defect complex and greatly alleviate the band-tail states of its defect complexes. The reason is that the P_S-3p (As_Se-4p) orbital not only has strong orbital coupling with the deep-level of the Sn_Zn defect, but also can properly accommodate its two residual electrons. Besides, the desired p-type characteristic of kesterites can be maintained in a considerable synthesizing region dominated by the effective P doping. This study provides a feasible way to eliminate the negative effects of Sn_Zn defects in kesterites, and the proposed passivation principle shows that realizing the strong orbital coupling between defect levels can efficiently improve the electrical properties of semiconductors.