We describe nickel tetrabenzoporphyrin ͑NiTBP͒ as a solution-processible organic semiconductor. Whereas porphyrins in an unmodified state are typically planar and insoluble, a precursor synthetic route ͑NiCP͒ was used to deposit thin films via solution. Amorphous, insulating thin films of NiCP were deposited, and thermally converted to polycrystalline, semiconducting NiTBP. Films were studied using optical absorption and microscopy, atomic force microscopy, and x-ray diffraction. Highly concentrated NiCP was shown to form large, needle-shaped crystals drop-cast from solution. NiTBP thin-film field-effect transistors fabricated from spun-cast films demonstrated charge-carrier field-effect mobilities on the order of 0.1 and 0.2 cm 2 / V s and accumulation threshold voltages of −19 and −13, in the linear and saturation regimes, respectively.
Tetrabenzoporphyrin films on indium-tin-oxide electrodes were prepared by continuous spin-coating of indium-tin-oxide electrodes with a soluble precursor, tetrabicyclo[2.2.2]octadiene-fused porphyrin, and subsequent thermal conversion of the precursor to tetrabenzoporphyrin by annealing the modified electrodes. When the tetrabenzoporhyrin-modified indium-tin-oxide working electrode was irradiated in a three-electrode system, using Pt as a counter electrode and Ag / Ag + as a reference electrode in the presence of hexyl viologen as an electron acceptor, a cathodic photocurrent was observed. A double layer structure consisting of tetrabenzoporphyrin and [6,6]-phenyl- C 61 butyric acid methyl ester (PCBM) films and a triple layer structure consisting of tetrabenzoporphyrin; a mixture of tetrabenzoporphyrin and PCBM; and PCBM films were also prepared on indium-tin-oxide electrodes by repeated spin-coating. The incident photon to photocurrent efficiency values of up to 6.8% were obtained for the triple layer structure, in which the mixed layer contained tetrabenzoporphyrin and PCBM molecules in a 7:3 ratio. Action spectra of the triple layer structure showed that visible light from 380 to 700 nm sensitized the system for photocurrent generation.
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