Heterojunction reconstruction via In doping towards high-efficiency CZTSSe solar cells

The Cu2ZnSn(S,Se)4 solar cells (CZTSSe) are emerging as a hot area of low-cost thin film photovoltaic technology owing to its non-toxicity and excellent photoelectric properties. However, the large open-circuit voltage deficit (Voc,deficit) caused by the inherently defective CdS/ CZTSSe heterojunction interface is still a huge challenge for improving power conversion efficiency. Herein, we reconstruct the heterojunction interface by inserting a CZTSSe:In into the CdS/CZTSSe heterojunction through an In2Se3 post-deposition treatment. The local occupation of In3+ at Zn2+ and Sn4+ sites decreases the disordered Zn- and Sn-related deep defects and generates benign InZn donors within CZITSSe transition layer simultaneously, which effectively enhances the surface p-to-n conversion. The combination of chemical and field-effect passivation regulates the charge extraction and passivates the charge recombination. As a result, the In element-buried absorber enables the Voc boost from 488 to 527 mV with an impressive active-area efficiency of 13.59 %. These results demonstrate the great potential of the In element-buried absorber in alleviating the Voc,deficit and enhancing the performance of CZTSSe solar cells.