Enhancing Photovoltaic Performance of Asymmetric Fused-Ring Electron Acceptor by Expanding Pyrrole to Pyrrolo[3,2-b]pyrrole

We propose a strategy to improve performance of unidirectionally extended fused-ring electron acceptors by using pyrrolo[3,2-b]pyrrole to replace pyrrole ring, and design two asymmetric nonfullerene acceptors 1PIC and 2PIC. Replacing pyrrole in 1PIC with pyrrolo[3,2-b]pyrrole remarkably red-shifts absorption peak by 109 nm, elevates the HOMO and LUMO energy levels, and improves electron mobility. The photovoltaic devices based on blend of PM6 donor and 2PIC acceptor exhibit power conversion efficiency as high as 12.6%, which is much higher than that of PM6:1PIC (3.53%), due to more efficient exciton generation and dissociation, faster and more balanced carrier transport and less charge recombination.