Variable‐Temperature X‐Ray Scattering Unveils the Solution Aggregation Structures and Processing Resiliency of High‐Efficiency Organic Photovoltaics with Iodinated Electron Acceptors
Mengyuan Gao, Kai Zhang, Wenchao Zhao, Shaoqing Zhang, Yiwen Li, Na Li, Chunming Yang, Yu Chen, Jianhui Hou, Long Ye
Abstract
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.