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Porphyrin–diindenothieno[2,3-b]thiophene alternating copolymer—a blue-light harvester in ternary-blend polymer solar cells



Porphyrin, despite chosen by Nature as light harvesting units, hasn't revealed its full potentials as a structural unit in porphyrin-incorporated polymers (PPors). A novel PPor was synthesized to investigate the origins of the low performances of PPor-based polymer solar cells (PSCs). The polymer features broad absorption in the blue-light region, because the diindenothieno[2,3-b]thiophene (DITT) unit extended the conjugation in the polymer backbone. PPor-DITT/PC71BM based PSCs have a high Voc (0.79 V). Their low Jsc and fill factor (FF) were attributed to the un-optimized morphology, as indicated by the photoluminescence quenching and atomic force microscopy (AFM) experiments. Using PPor-DITT as a blue-light harvesting dopant in an amorphous host leverage the strong 400–550 nm absorption of PPor-DITT and circumvent the difficulties in reaching optimized morphology in the PPor/PCBM thin films. An addition of 2 wt % of PPor-DITT in ternary-blend PSCs resulted in a 10 % increase of external quantum efficiency (EQE) in the blue-light region. However, in a crystalline host, the dopant decreased the crystallinity of the host and led to large drops in FF and power conversion efficiencies (PCEs). The study provides an alternative route and expands the application of PPors in PSCs as a blue-light harvester in ternary-blend PSCs using amorphous polymers as host. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012