Gradient Bandgap Modification for Highly Efficient Carrier Transport in Antimony Sulfide-Selenide Tandem Solar Cells

Antimony chalcogenide thin-film solar cells have been developed rapidly in recent years. In particular, antimony sulfide-selenide (SbSSe) solar cells have attracted significant attention based on their advantages of simple preparation, excellent photoelectric performance, and tunable bandgaps. In this study, by applying energy-band engineering technologies, we achieved carrier transport balance and light absorption balance for SbSSe single- and triple-junction solar cells, respectively. Test results demonstrate that the photoelectric conversion efficiency (PCE) of SbSSe solar cells with a front-gradient Se content structure is improved from 13.14% to 16.16% compared to a baseline SbSSe solar cell. This improvement is attributed to the additional electric field induced by the gradient bandgap, which assists in carrier transport. Eventually, the balance of carrier transport is realized by adjusting the drift velocities of holes and electrons simultaneously, thereby surpassing carrier recombination and improving the short-circuit current density (Jsc) and fill factor (FF) of solar cells. Then, an SbSSe solar cell with an advanced gradient bandgap structure was applied as the middle-cell in an antimony chalcogenide triple-junction solar cell (ATSC). Based on the high Jsc and FF advantages of SbSSe sub-cells with front-gradient Se content structure, the uniform absorption of sunlight in each sub-cell and current matching of tandem solar cells could be easily realized. Consequently, the PCE of the ATSCs exhibits an enhancement from 17.34% to 19.51%. Our results demonstrate that the application of energy-band engineering technology can effectively improve device performance, providing theoretical guidance for the refined design and nanomanufacturing development of antimony chalcogenide solar cells.