Synthesis of a soluble n-type cyano substituted polythiophene derivative: A potential electron acceptor in polymeric solar cells

A novel, easy processable n-type polythiophene derivative poly(3-cyano-4-hexylthiophene) (P3CN4HT) was synthesized and characterized with different spectroscopic techniques such as H-1 NMR, size exclusion chromatography, Fourier transformed infrared spectroscopy (FT-IR), UV-vis, photoluminescence, and cyclic voltammetry. P3CN4HT is very soluble in common organic solvents (tetrahydrofyran, chloroform) and has high electron affinity. Systematic photoluminescence measurements were used to characterize several electron donating polymers such as poly(2-methoxy-5-[3',7'-dimethyloctyloxy]-p-phenylene vinylene) (MDMO-PPV), regioregular poly(3-octylthiophene) (P3OT), and poly(4,4'-dihexylcyclopentadithiophene) (PCPDT). When P3CN4HT was employed in blends as the electron acceptor, we observed complete photoluminescence quenching for both MDMO-PPV:P3CN4HT and P3OT:P3CN4HT mixtures. Preliminary photovoltaic measurements demonstrated power conversion efficiency as high as 0.014% for the MDMO-PPV:P3CN4HT blend without any solvent screening, thickness optimation, or post-fabrication annealing of the devices.