Phenylene-bridged perylenediimide-porphyrin acceptors for non-fullerene organic solar cells

New perylenediimide-porphyrin acceptors, 4PDI-ZnP and 2PDI-ZnP, have been facilely synthesized by acid-catalyzed condensation of perylenediimide-substituted benzaldehyde with pyrrole and dipyrromethane, respectively, and subsequent Zn(ii)-complexation. 4PDI-ZnP with four perylene diimide (PDI) moieties appended onto the zinc(ii)-porphyrin core shows higher electron mobility than 2PDI-ZnP with only two PDI units. The π-conjugation between PDI and porphyrin is significantly weakened by the phenylene linkage twisting them due to steric hindrance, which renders the absorption features from porphyrin and PDI undisturbed in the range of 385-600 nm. For spectral absorption properties perfectly complementary to the common polymer donor PTB7-Th, the two acceptors have been evaluated together with PTB7-Th in non-fullerene bulk heterojunction organic solar cells (BHJ OSCs). High power conversion efficiency of 9.64% was achieved using the blend of 4PDI-ZnP:PTB7-Th for optimal visible sunlight harvesting, favorable morphological properties and efficient charge dissociation upon photon absorption. This represents a new benchmark photovoltaic performance for PDI acceptors and PTB7-Th donor systems. It should be noted that the porphyrin core not only acts as a scaffold for PDI moieties, but also contributes the light-harvesting in near-ultraviolet and violet regions, which is unambiguously demonstrated in single-component BHJ OSCs based on the two acceptors.