Side-chain effects on phenothiazine-based donor-acceptor copolymer properties in organic photovoltaic devices

A series of new phenothiazine-based donor-acceptor copolymers, P1 and P2, were synthesized via a Suzuki coupling reaction. The weight-averaged molecular weights (M(w)) of P1 and P2 were found to be 16,700 and 16,100, with polydispersity indices of 1.74 and 1.39, respectively. The UV-visible absorption spectra of the polymer thin films contained three strong absorption bands in the ranges 318-320 nm, 430-436 nm, and 527-568 nm. The absorption peaks at 320 and 430 nm originated mainly from the phenothiazine-based monomer units, and the longer wavelength absorption band at 527-568 nm was attributed to the increased effective conjugation length of the polymer backbones. Solution-processed field-effect transistors fabricated with these polymers exhibited p-type organic thin film transistor characteristics. The field-effect mobilities of P1 and P2 were measured to be 1.0 x 10(-4) and 7.5 x 10(-5) cm(2) V(-1) s(-1), respectively, with on/off ratios in the order of 10(4) for all polymers. A photovoltaic device in which a P(2)/PC(71)BM (1/3) blend film was used as the active layer exhibited an open-circuit voltage (V(OC)) of 0.70 V, a short-circuit current (J(SC)) of 6.79 mA cm(2), a fill factor of 0.39, and a power conversion efficiency of 1.86% under AM 1.5 G (100 mW cm(-2)) illumination. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 649-658, 2012