Synthesis and properties of phenothiazylene vinylene-based polymers: New organic semiconductors for field-effect transistors and solar cells

Abstract

A series of new phenothiazylene vinylene-based semiconducting polymers, poly[3,7-(4′-dodecyloxyphenyl)phenothiazylene vinylene] (P1), poly[3,7-(4′-dodecyloxyphenyl)phenothiazylene vinylene-alt-1,4-phenylene vinylene] (P2), and poly[3,7-(4′-dodecyloxyphenyl)phenothiazylene vinylene-alt-2,5-thienylene vinylene] (P3), have been synthesized via a Horner-Emmons reaction. FTIR and 1H NMR spectroscopies confirmed that the configurations of the vinylene groups in the polymers were all-trans (E). The weight-averaged molecular weights (Mw) of P1, P2, and P3 were found to be 27,000, 22,000, and 29,000, with polydispersity indices of 1.91, 2.05, and 2.25, respectively. The thermograms for P1, P2, and P3 each contained only a broad glass transition, at 129, 167, and 155 °C, respectively, without the observation of melting features. UV–visible absorption spectra of the polymers showed two strong absorption bands in the ranges 315–370 nm and 450–500 nm, which arose from absorptions of the phenothiazine segments and the conjugated main chains. Solution-processed field-effect transistors fabricated from these polymers showed p-type organic thin-film transistor characteristics. The field-effect mobilities of P1, P2, and P3 were measured to be 1.0 × 10−4, 3.6 × 10−5, and 1.0 × 10−3 cm2 V−1 s−1, respectively, and the on/off ratios were in the order of 102 for P1 and P2, and 103 for P3. Atomic force microscopy and X-ray diffraction analysis of thin films of the polymers show that they have amorphous structures. A photovoltaic device in which a P3/PC71BM (1/5) blend film was used as the active layer exhibited an open-circuit voltage (VOC) of 0.42 V, a short circuit current (JSC) of 5.17 mA cm−2, a fill factor of 0.35, and a power conversion efficiency of 0.76% under AM 1.5 G (100 mW cm−2) illumination. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 635–646, 2010