Exploring thieno[3,4-c]pyrrole-4,6-dione combined thiophene as π-bridge to construct non-fullerene acceptors with high VOC beyond 1.0 V

Abstract

Thieno[3,4-c]pyrrole-4,6-dione (TPD) unit has been widely used to construct a great deal of D-π-A p-type copolymers due to its strong electron-deficient property. However, there are limited reports on the TPD-based n-type materials, particularly small molecule non-fullerene acceptors (NFAs), mainly due to the time-consuming synthetic routes. Herein, two new TPD-based NFAs named as TPD-Th1 and TPD-Th3 were successfully obtained, adopting indacenodithiophene (IDT) as the central core and rhodanine (R) or 2-(1,1-dicyanomethylene)rhodanine (RCN) as the terminal electron-withdrawing unit. Both TPD-Th1 and TPD-Th3 exhibit highly planar structure due to the intramolecular noncovalently conformational locking between the O atom on the TPD unit and H atoms of two neighboring thiophene ring. The optimized PTB7-Th:TPD-Th3 photovoltaic devices show a much higher power conversion efficiency (PCE) of 5.53% in comparison with PTB7-Th:TPD-Th1 (PCE = 0.62%). The latter lower PCE could be attributed to the unmatched LUMO energy levels. Our results open a unique way to utilize TPD to construct small molecule NFAs to achieve a relatively high VOC and PCE.