Enhanced performance of ternary organic solar cells with a wide bandgap acceptor as third component
Two n-type organic semiconductor (n-OS) acceptors, C8-SF and Y-MODF, were designed and synthesized for the application in organic solar cells (OSCs). C8-SF shows a lower lowest unoccupied molecular orbital (LUMO) energy level and lower bandgap with absorption edge at 822 nm. Y-MODF possesses a relatively larger bandgap, higher LUMO and lower HOMO (the highest occupied molecular orbital) energy levels than C8-SF. With polymer PM6 as donor, the OSC with C8-SF as acceptor delivers a power conversion efficiency (PCE) of 11.59% with a lower open circuit voltage (Voc) of 0.787 V, while the device with Y-MODF as acceptor exhibits a lower PCE of 8.63% but a higher Voc of 0.984 V benefitted from the higher LUMO of the Y-MODF acceptor. Then, a series of ternary OSCs were fabricated with PM6:C8-SF as the host system and Y-MODF as a third component. The optimal ternary OSCs with 25% Y-MODF incorporated in acceptor reach a higher PCE of 13.39%, with improved Voc of 0.845 V, Jsc of 20.88 mA cm−2 and FF of 75.87%. It was found that adding Y-MODF into the PM6:C8-SF binary system suppressed monomolecular recombination and improved the utilization of 450-600 nm range photons. Molecular packing is further optimized with more balanced hole and electron transport, thus results in the enhanced Jsc and FF for the ternary OSCs. These results indicate that addition of wide bandgap acceptor with higher LUMO energy level into a binary donor/acceptor system may have potential for the Voc and PCE improvement of the ternary OSCs.