A water/alcohol-soluble conjugated porphyrin small molecule as a cathode interfacial layer for efficient organic photovoltaics

A water/alcohol soluble conjugated porphyrin small molecule, FNEZnP-OE, in which two amino-functionalized fluorenes (9,9-bis(30-(N,N-dimethylamino) propyl)-2,7-fluorenes) are linked to a porphyrin core substituted with two polar 3,4-bis-[2-(2-methoxy-ethoxy)-ethoxy]-phenyls by ethynylene linkages, is designed and synthesized as a cathode interfacial material (CIM) for bulk heterojunction organic solar cells. The PTB7/PC71BM-and PTB7-Th/PC71BM-based devices with FNEZnP-OE as the electron transport layers (ETLs) exhibit power conversion efficiencies (PCEs) of 8.52% and 9.16%, respectively, which are increased by 47% and 41% compared to the devices with no ETL (5.78% and 6.50%, respectively). Most significantly, these PCEs are increased by 13.6% and 8%, respectively, over those with the widely used polymer ETL PFN (poly[(9,9-bis(30-(N, N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9-ioctylfluorene)]). The outstanding performance of FNEZnP-OE CIM is contributed by not only the polar groups of 9,9-bis(30-(N, N-dimethylamino) propyl)-2,7-fluorenes and 3,4-bis-[2-(2-methoxyethoxy)-ethoxy]-phenyls but also the porphyrin-relating pi-conjugated backbone of FNEZnP-OE induced by the ethynylene linkages, demonstrating that functionalized porphyrins are very promising interfacial materials.