18.73% efficiency organic solar cells with a medium bandgap acceptor as a third component

To improve the photovoltaic performance of organic solar cells (OSCs), it is important to optimize all relevant parameters. However, it is challenging work to select suitable semiconductors for constructing a desirable active blend film with realizable device performance. In this study, we used an effective methodology to enhance the photovoltaic performance of OSCs by adding a third component (IT-M) with a medium bandgap. The addition of IT-M improved the blend film morphology, which helped to enhance light absorption and exciton dissociation as well as suppress charge recombination. The compatibility between IT-M and BTP-eC9 was found to be satisfactory, resulting in optimized phase separation and cascaded energy level alignment between the two acceptors. This in turn facilitated balanced charge transport. Additionally, a small amount of IT-M was found to be sufficient to achieve desirable blend film phase separation and molecular stacking, which is advantageous in forming interconnected and continuous network structures. As a result, the optimized OSCs achieved an impressive power conversion efficiency of 18.73% and all-around improved photovoltaic performance parameters. This study demonstrates an effective approach to improve the device performance of OSCs by introducing a suitable second acceptor.