New alternating copolymers of fluorene and triphenylamine bearing terthiophene and acceptor groups in the side chains: Synthesis and photovoltaic properties

A series of conjugated copolymers (P1 and P2-CN–P4-CN) were prepared, in which two kinds of side chains were designed: one was the repeating units similar to that of P3HT, with the aim to increase the compatible with PC61BM and the hole mobility; another one was the acceptor groups connected with the electron-rich backbone through the conjugated 3,4-ethylenedioxythiophene bridge, in order to broaden the absorption and lower the LUMO level. By controlling the ratios of these two kinds of side chains, the absorption band of the resultant conjugated polymers could be fine-tuned, while their energy levels nearly remained unchanged. As the result, the performance of the corresponding devices increased first, then decreased, indicating that there would be a balance between the different function of these two side chains.