The Side-chain Effects on Photovoltaic Properties of Copolymers Based on Phenothiazine and Thiophene

In this study, the alternating conductive polymers based on phenothiazine and bithiophene unit, poly[(N-10-dodecyl-phenothiazin-3,7-ylene)-alt-(2,2'-bithiophen-5-yl)] (P1) and poly[(N-10-dodecyl-phenothiazin-3,7-ylene)-alt-(4,4'-didodecyl-2,2'-bithiophen-5-yl)] (P2), were synthesized by Suzuki coupling reaction in the presence of palladium catalyst. The structures of synthesized compounds were confirmed by H-1 NMR. The optical, electrochemical properties of synthesized polymers were investigated by UV-Vis, cyclic voltammetry (CV). The optical band gap of 2.22 eV and 2.50 eV was obtained from absorption onset of UV-Vis spectrum. Then, the two devices using blends of the polymer, as a donor, and PC71BM, as an acceptor, were fabricated by spin-coating. The device with a P1:PC71BM (1:4, w/w) as an active layer exhibited the best performance with an open circuit voltage (V-OC) of 0.68 V, short circuit current (J(SC)) of 3.5 mA/cm(2), fill factor (FF) of 31.8 % and power conversion efficiency (PCE) of 0.74 %.