Donor–Acceptor-Type Low Bandgap Polymer Carrying Phenylazomethine Moiety as a Metal-Collecting Pendant Unit: Open-Circuit Voltage Modulation of Solution-Processed Organic Photovoltaic Devices Induced by Metal Complexation

A novel low-bandgap conjugated polymer with the phenylazomethine moiety as a pendant metal-collecting unit (PImCDTBT) was synthesized via Suzuki cross-coupling copolymerization. Its basic physicochemical properties were revealed, and the optical bandgap and highest occupied molecular orbital (HOMO) energy levels were estimated to be 1.73 eV and −5.36 eV, respectively. PImCDTBT successfully assembles metal ions on its phenylazomethine site, as evidenced by a spectral change similar to that of its monomeric model compounds. In a bulk heterojunction photovoltaic device, the open-circuit voltage was clearly enhanced from 0.46 to 0.52 V by complexation of PImCDTBT, with only 1 wt % of SnCl₂. This was due to a change in either the electronic state of the polymer or its environment by complexing with the cationic Sn²⁺ ion.