Variable-Temperature X-Ray Scattering Unveils the Solution Aggregation Structures and Processing Resiliency of High-Efficiency Organic Photovoltaics with Iodinated Electron Acceptors.

Polymer photovoltaics are promising for low-cost, flexible, and lightweight power supplies. Their performance is heavily influenced by the morphology of the polymer: acceptor blend, where the aggregation structures of both components play a crucial role in charge generation, transport, and overall device performance. This study probes and resolves the solution aggregation behavior and processing resilience of high-efficiency polymer photovoltaics incorporating an iodinated electron acceptor, BO-4I, using variable-temperature small-angle X-ray scattering and neutron scattering. By comparing BO-4I with its fluorinated counterpart, it is found that BO-4I exhibits excellent solution processing stability, whether in chlorobenzene or toluene. In addition, temperature-induced change in the donor:acceptor blend aggregation structure leads to significant alterations in film morphology, ultimately affecting device performance. Particularly, the stable solution aggregation structure of the BO-4I system confers processing resilience to device performance and achieves higher long-term device stability. Combining film structural analysis and device performance characterization, a structural inheritance is identified from solution to film, and determined that a organic photovoltaics polymer aggregate length of 27 ± 3 nm in solution is a key feature for achieving optimal efficiency in polymer photovoltaics. These findings provide valuable insights and guidance for designing future polymer photovoltaic systems.