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 (J(SC)) value is usually counteracted by a decrease in the open-circuit voltage (V-OC), 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 tradeoff between the J(SC) and V-OC. 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 V-OC 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 J(SC) and V-OC values and improved device stability.