Synthesis and Photovoltaic Properties of Bithiazole-Based Donor−Acceptor Copolymers

Three new donor−acceptor (D−A) alternative copolymers containing bithiazole acceptor unit and the donor unit of carbazole (P1), dithienopyrrole (P2), or dithienosilole (P3) were synthesized for the application as donor materials in polymer solar cells (PSCs). The copolymers were characterized by TGA, UV−vis absorption, electrochemical cyclic voltammetry and photovoltaic measurements. The results indicate that the donor units in the copolymers influence the bandgaps, electronic energy levels and photovoltaic properties of the copolymers significantly. Among the three copolymers, P3 with the donor unit of dithienosilole shows an absorption spectrum similar to that of P3HT, suitable HOMO energy level at −5.18 eV, a higher hole mobility of 3.07 × 10−4cm2/V s and promising photovoltaic properties. The power conversion efficiency of the PSC based on P3:PC70BM=1:1(w/w) reached 2.86% with short circuit current of 7.85 mA/cm2, open circuit voltage of 0.68 V, and fill factor of 0.535, under the illumination of AM1.5, 100 mW/cm2.