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 (Mw) 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 × 10−4 and 7.5 × 10−5 cm2 V−1 s−1, respectively, with on/off ratios in the order of 104 for all polymers. A photovoltaic device in which a P2/PC71BM (1/3) blend film was used as the active layer exhibited an open‐circuit voltage (VOC) of 0.70 V, a short‐circuit current (JSC) 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. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 The new copolymers with phenothiazylene vinylene donors and DTBT acceptors were synthesized and the effects of side chains on the photophysical, electrochemical, and OPV properties were studied.