Cu-Zn Cation Disorder in Kesterite Cu2ZnSn(S x Se1-x )4 Solar Cells

Cu-Zn cation disorder plays a vital and controversial role in kesterite CuZnSn(S1-xSex)(4) solar cells. We demonstrate using density functional theory and nonadiabatic molecular dynamics simulations that the Cu-Zn disorder across different planes (i.e., Cu-Sn and Cu-Zn planes) is significantly more detrimental to device performance than the case when disorder is confined only to the Cu-Zn planes. The main reason is that different plane disorder induces a significant elongation of Sn-S/Se bond lengths, leading to a downshift of the conduction band minimum, decreasing the band gap, and reducing the optical absorption. Moreover, Cu-Zn disorder across different planes accelerates nonradiative electron-hole recombination and decreases charge carrier lifetime due to the reduction of the band gap and enhanced electron-vibrational interaction. Our results provide a theoretical explanation for the influence of Cu-Zn disorder on material performance and offer valuable insight into the design of more efficient solar cells.