Description Non-fullerene acceptors (NFAs) are currently a major focus of research in the development of bulk-heterojunction organic solar cells (OSCs). In contrast to the widely used fullerene acceptors (FAs), the optical properties and electronic energy levels of NFAs can be designed and readily tuned. NFA-based OSCs can also achieve greater thermal stability and photochemical stability, as well as longer device lifetimes, than their FA-based counterparts.Recent developments have led to a rapid increase in power conversion efficiencies for NFA OSCs, with values now exceeding 15% in a single junction cell, and >17% for a tandem cell, demonstrating the viability of using NFAs to replace FAs in next-generation high-performance OSCs.IDT-2BR is a medium-high bandgap nonfullerene acceptors (NFAs). It was reported that IDT-2BR could produce a high power conversion efficiency (PCE) of over 10% when used with low-bandgap p-type polymer PTB7-Th (Product No. 794333). A prominent feature of this blend is the very small energy loss (< 0.6 eV) in the cell, which allows for a very high open circuit voltages in the device (> 1 V).Ternary blend organic solar cells (OSCs) with photoresponses beyond 1000 nm can be fabricated using PTB7-Th as donor and ultralow-bandgap F8IC and medium-high bandgap IDT-2BR as NFAs. A PCE of 12.1% has been achieved by such a ternary device with 20% IDT-2BR content in acceptors. In this work, IDT-2BR was found to contribute simultanously to the improvement of the open-circuit voltage (VOC), short-circuit (JSC) and fill factor (FF) of the PTB7-Th/F8IC blend, due to smaller energy offset for charge separation, suppressed charge recombination, and imporved light absorption. Improved packing due to the coexsitence of F8IC and IDT-2BR leads to higher mobilities and more balanced charge transport, which contribute to the improved FF as well.Additionaly, blends with IDT-2BR have been found to be thermally stable at 150 Celsius.A ternary blend using both IDT-2BR and fullerene based acceptor: PC71BM (Product No. 684465) has also reached a PCE over 12%.
