Molecular Ordering and Performance of Ternary Nonfullerene Organic Solar Cells via Bar-Coating in Air with an Efficiency over 13%

An in situ spectroscopy ellipsometry technique is utilized to probe the molecular ordering sequences of PBDB-T2F/IT-4F/COi8DFIC ternary photovoltaic blends fabricated by bar-coating in air. The time-resolved dynamics show that the primary electron acceptor IT-4F aggregates ahead of the secondary acceptor COi8DFIC in the bar-coated photoactive layer, although the latter has much stronger crystallization ability. Wetting coefficient analysis supports that COi8DFIC locates at the interface between the host components PBDB-T-2F and IT-4F. We demonstrate that the suitable degree of phase separation with the presence of 20 wt % COi8DFIC facilitates exciton dissociation and charge transfer, leading to a remarkable power conversion efficiency of 13.2% as well as excellent stability of ternary organic solar cells (OSCs), which is among the highest reported efficiency for OSCs that were fabricated by scalable solution-casting in ambient conditions.