Angular-Shaped Dithienonaphthalene-Based Nonfullerene Acceptor for High-Performance Polymer Solar Cells with Large Open-Circuit Voltages and Minimal Energy Losses

The utilization of low bandgap copolymers has been considered as one of the most efficient ways to increase power conversion efficiencies (PCEs) of fullerene-based polymer solar cells (PSCs). However, an increase in the short-circuit current (JSC) value is usually counteracted by a decrease in the open-circuit voltage (VOC), which limits a further PCE enhancement of fullerene-based PSCs. As a result, nonfullerene acceptors with wide-range tunable energy levels are used as alternatives to the traditional fullerene acceptors to overcome the negative trade-off between the JSC and VOC. Here, a novel nonfullerene acceptor is developed by using an angular-shaped dithienonaphthalene flanked by electron-withdrawing 3-ethylrhodanine units via benzothiadiazole bridges. The obtained nonfullerene acceptor exhibits a high-lying lowest unoccupied molecular orbital level of −3.75 eV with enhanced absorption. In combination with a benchmark low bandgap copolymer (PTB7-Th), a high PCE of 9.51% with a large VOC of 1.08 V was achieved for the nonfullerene PSCs, demonstrating an extremely low energy loss of 0.50 eV, which is the lowest among all high-performance (PCE > 8%) polymer-based systems with similar optical bandgaps. The results demonstrate the bright future of our nonfullerene acceptor as an alternative to the fullerene derivatives for PSCs with large JSC and VOC values and improved device stability.