Synthesis and photovoltaic properties of two-dimensional conjugated polythiophene derivatives presenting conjugated triphenylamine/thiophene moieties

In this study we synthesized three two-dimensional (2-D) polythiophene derivatives (PTs), namely PTBPTPA, PTStTPA, and PTCNStTPA, featuring three different conjugated units-biphenyl (BP), stilbene (St), and cyanostilbene (CNSt), respectively-in the polymer backbones and presenting conjugated triphenylamine/thiophene (TPATh) moieties on the side chains. In addition, we also synthesized three conjugated BP-, St-, and CNSt-based main-chain-type conjugated polymers (PTBP, PTSt, and PTCNSt, respectively). Incorporating the St and CNSt moieties into the polymer backbones and appending TPATh units induced high degrees of intramolecular charge transfer within the conjugated frameworks of the polymers, thereby resulting in lower band gap energies and red-shifting of the maximal UV-Vis absorption wavelengths. Moreover, the energy levels of the highest occupied molecular orbitals of the BP-, St-, and CNSt-based main-chain-type and 2-D PTs were lower than that of P3HT, implying that they would be applicable for the preparation of polymer solar cells (PSC) with greater open-circuit voltages. The photovoltaic performances of PSCs fabricated from blends of the 2-D PTs and the fullerene derivative PC61BM were superior to those of PSCs based on the main-chain-type polymer/PC61BM blends.