13.2% Efficiency of Organic Solar Cells by Controlling Interfacial Resistance Resulting from Well-Distributed Vertical Phase Separation

Two strategies were investigated to improve the efficiency of organic solar cells (OSCs) with the aim of controlling the interfacial resistance in the devices: the use of a ternary active layer and the introduction of conjugated polymers. The ternary active layer was formed by introducing PC71BM between a high-performance non-fullerene photoactive material P­(Cl–Cl) (BDD = 0.2) and the IT-4F-based binary active layer, thereby reducing the interfacial resistance between the donor and acceptor via vertical phase separation. Furthermore, the introduction of the conjugated polymer PFN-Br created a well-dispersed separation attributable to enhancement of the interfacial contact with the active layer and simultaneous reduction of the interfacial resistance. Consequently, the synergetic effect of the ternary active layer and PFN-Br enhanced the short-circuit current density (J SC) and fill factor (FF) to realize a power conversion efficiency (PCE) of 13.2%.