Oligomers Comprising 2‑Phenyl‑2H‑benzotriazole Building Blocks for Solution-Processable Organic Photovoltaic Devices

In the past, benzotriazole acceptor units have been incorporated successfully into donor–acceptor polymers for highly efficient photovoltaic devices. Here, we explore 2-phenyl-2H-benzotriazole oligomers as model systems for donor–acceptor polymers. We designed and synthesized acceptor–donor–acceptor oligomers incorporating 2-phenyl-2H-benzotriazole acceptor and naphthodithiophene donor units. Supported by quantum chemical calculations we investigated the optoelectronic properties, such as electronic levels and intramolecular charge transfer, by means of optical and fluorescence spectroscopy. We built bulk-heterojunction solar cells comprising these oligomers and [6,6]-phenyl C61-butyric acid methyl ester. In doing so, the film-forming conditions were optimized as the absorber layer morphology is strongly affected by the deposition conditions, in particular drying time and drying temperature.