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

The Cu 2 ZnSn(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 ( V oc,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 In 2 Se 3 post-deposition treatment. The local occupation of In 3+ at Zn 2+ and Sn 4+ sites decreases the disordered Zn- and Sn-related deep defects and generates benign In Zn 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 V oc 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 V oc,deficit and enhancing the performance of CZTSSe solar cells.