Trade-Off between Exciton Dissociation and Carrier Recombination and Dielectric Properties in Y6-Sensitized Nonfullerene Ternary Organic Solar Cells

Organic photovoltaics (OPVs) have emerged as a promising renewable energy generation technology in past decades. However, the deep understanding of the details in exciton dissociation and carrier recombination in ternary organic solar cells (OSCs) is still lacking. Herein, a novel ternary OSC based on a PTB7-Th:Y6:ITIC blend with a power conversion efficiency (PCE) enhancement of 29% is reported. A trade-off is surprisingly found to exist between the exciton dissociation and carrier recombination process. The addition of nonfullerene acceptor Y6 in the ternary blend is found to create an efficient exciton dissociation process but accelerates the free carrier recombination process. Dielectric properties are also studied for ternary OSCs. The addition of Y6 into the binary blend is found to tune down the dielectric constant of the active layer and as a result accelerates the carrier recombination. The best performance is obtained for PTB7-Th:Y6(5 wt%):ITIC(95 wt%)-based ternary devices. In addition to its balanced charge carrier mobility and efficient charge extraction process, PTB7-Th:Y6(5 wt%):ITIC(95 wt%)-based ternary devices reach a balance in the trade-off between the exciton dissociation and carrier recombination process and thus achieve the highest short-circuit current density (J(sc)) value.