Lanthanum-induced synergetic carrier doping of heterojunction to achieve high-efficiency kesterite solar cells

In kesterite Cu2ZnSn(S, Se)4 (CZTSSe) solar cells, the insufficient CdS/CZTSSe heterojunction built-in electric field due to the low carrier concentration is an important factor limiting the photoelectric conversion performance. Herein, we introduce an extrinsic La3+ incorporation to realize a synergetic carrier doping of this heterojunction. By forming shallow LaCd and LaSn substitution defects, electron and hole concentration in CdS and kesterite has been obviously increased, which effectively improves the electric property and interface charge transfer of the heterojunction. The resulting reduction in the minority carrier loss has finally realized a high cell efficiency of 13.9% at room temperature. Moreover, the carrier doping allows the heterojunction to work in a much wider temperature region and the cell obtains an impressively high efficiency of 22% at 130 K.