Promoting solution-processed CdTe nanocrystal solar cells via rationally controlled copper doping†

The back contact of p-type semiconductors and metal electrodes have always been a difficulty in fabricating photovoltaics with high performance. The incompatibility of high HOMO with a metal work function may lead to Schottky contact at a back semiconductor–metal interface and lead to device inversion. Thus, the performance of the photovoltaic is restricted, especially for solution-processed CdTe NC solar cells. In our research, we proposed using Cu salts as a Cu source to dope CdTe NCs and improve the back contact interface. Enhanced performance in solution-processed NC solar cells is achieved by introducing an engineered Cu salt layer (CuCl₂ and CuBr₂). Exceptional performance is attained with the optimized CdTe NC doped with CuCl₂, exhibiting a high short-circuit current of 20.20 mA cm⁻², an open-circuit voltage of 0.58 V, and a fill factor of 53.74%, resulting in a power conversion efficiency of 6.3%. These results represent a significant improvement over the control group. Through detailed first principles studies and experimental verification, we demonstrate that the copper halide-doped CdTe NC thin film is promising to promote the carrier concentration of the CdTe NC and suppress carrier recombination by improving band alignment at the back contact interface.