Recently, Professor Wu's research group published a new research of “Ag, Ge Dual gradient Substitution for low-energy Loss and High Efficiency Kesterite Solar Cells” in the Journal of Materials Chemistry A (J. Mater. Chem. A 2020, DOI: 10.1039/D0TA06318E).

A major obstacle hindering further development of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is the inherent recombination losses that occur both via bulk defects and charge extraction interfaces. So, in this paper, a generic Ag, Ge dual-gradient absorber architecture is proposed, involving a downshift of absorber VBM at the front contact and an upshift of absorber CBM at the back contact, to improve device performance. The experiment results show that the substitution of Cu by Ag allows for larger band bending at the p–n junction, and the substitution of Sn by Ge imposes an additional drift field within the quasi-neutral region. Additionally, the Ag and Ge ions diffusing into the bulk absorber passivate the deleterious CuZn and CuSn deep-level defects. In turn, accelerated charge extraction, transport and minimized recombination loss offered surprising gains in Voc and Jsc, and the dual-gradient device achieved a maximum efficiency of 12.26% with an improved Voc,deficit of 553 mV. This research result obtains the highest efficiency in the amine-mercaptan solution system at present. And it has important significance for the subsequent improvement of the interface performance and the optimization of the absorption layer structure in CZTSSe thin film solar cells.

The first author of this paper is Dr. Fu Junjie of Key Laboratory of Special Functional Materials, and the corresponding authors are Professor Wu Sixin and Associate Professor Kou Dongxing. This work is supported by the National Natural Science Foundation of China, the Science and Technology Department of Henan Province, the Education Department of Henan Province and Henan University.