Enabling Efficient Tandem Organic Photovoltaics with High Fill Factor via Reduced Charge Recombination

Compared with inorganic photovoltaics, organic photovoltaics (OPVs) still have a low fill factor (FF) that restricts their power conversion efficiency (PCE). The FF is determined by the resistances that are influenced by carriers recombination. In this work, the tandem structure is demonstrated to be a feasible solution to improve the FF of OPVs. The recombination losses of subcells in the tandem structure are reduced and consequently improves the FF. When the two subcells are stacked in a tandem structure, the highest value of the FF reaches 76.6%, much higher than that of 66.1% achieved by its single junction device. Finally, a PCE of 14.1% with a FF of 73.6% is achieved in a tandem OPV after optimizing the thickness of each active layer. This work not only demonstrates the inherent mechanism for a higher FF in tandem OPVs but also presents a feasible solution for high-performance photovoltaic devices.