Influence of NaErF4@NaYF4 nanoparticles doping on performances of Cu2ZnSn(S,Se)4 solar cell

We report the improvement of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells via doping NaErF4@NaYF4 (NEYF) nanoparticles. The NEYF nanoparticles were doped into the CZTSSe layer as an absorber in a solar cell with the conventional structure of SLG/Mo/absorber/CdS/i-ZnO/ITO/Al. It is found that NEYF doping could increase open circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF) of the CZTSSe solar cell, which enables the best power conversion efficiency (PCE) increase from 4.03% of CZTSSe solar cell up to 7.10%. For the solar cell with a NEYF-doped CZTSSe (CZTSSe:NEYF) absorber, the improved VOC and JSC are mainly due to the decrease in reverse saturation current density (J0) and the improvement in photocurrent density (JL) brought by NEYF doping, while the enhancement in fill factor should be ascribed to the decreased series resistance (Rs). The mechanisms of change in the J0, JL, Rs and band gap (Eg) from NEYF doping are discussed in detail by comparative study of composition, structure and electrical properties of the CZTSSe:NEYF and CZTSSe films as well as interfacial structures of CZTSSe:NEYF and CZTSSe solar cells in the present work.