Extension of Light-Harvesting Area of Bulk-Heterojunction Solar Cells by Cosensitization with Ring-Expanded Metallophthalocyanines Fused with Fluorene Skeletons

Near-IR absorbing zinc fluorenocyanine complexes 1-3 were designed and synthesized as a cosensitizer for bulk-heterojunction solar cells. Fusing fluorene rings with the porphyrazine rings resulted in narrower band gap and stabilization of both the HOMO and LUMO energy levels compared with a zinc phthalocyanine complex. The synthesized fluorenocyanines 1-3 were incorporated into bulk-heterojunction solar cells based on regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61. The addition of 3 decorated with eight alkyl chains resulted in improved device performance with a 16% enhancement of the short circuit current compared with that of the reference cell without 3.