Organic Photovoltaics Based on Poly(3,4-phenylenedioxy-2,5-thienylenevinylene)s (第57回論文特集号 有機系および有機 : 無機太陽電池の現状と課題) Organic Photovoltaics Based on Poly(3,4-phenylenedioxy-2,5-thienylenevinylene)s

Poly(3,4-phenylenedioxy-2,5-thienylenevinylene)s with a fluorine substituent at the phenylene moiety (PPhDOTFV) and without the substituent (PPhDOTV) were synthesized by Stille coupling polymerization. They exhibited good solubility in common organic solvents owing to a branched alkyl chain at the phenylene moiety and a narrow optical bandgap of 1.66 eV due to an increased conjugated length caused by the vinylene bridge. Both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PPhDOTFV were 0.2 eV deeper than those of PPhDOTV. Organic photovoltaic cells (OPVs) using PPhDOTV:PC₇₀BM exhibited a short-circuit current density (<i>J</i>_sc) of 3.30 mA cm⁻², an open-circuit voltage (<i>V</i>_oc) of 0.52 V, and a power conversion efficiency of 0.91%, as compared to 1.62 mA cm⁻², 0.68 V, and 0.45%, respectively, for OPVs using PPhDOTFV:PC₇₀BM. The <i>J</i>_sc value of PPhDOTV-based OPVs was higher than that of PPhDOTFV-based OPVs because of a large LUMO energy offset between PPhDOTV and PC₇₀BM. On the other hand, the <i>V</i>_oc value of PPhDOTV-based OPVs was lower than that of PPhDOTFV-based OPVs because of a small energy difference between the HOMO level of PPhDOTV and the LUMO level of PC₇₀BM.