Li Qian, Wang Rui, Yu Tao, Wang Xiaoyong, Zhang Zhi-Guo, Zhang Yuan, Xiao Min, Zhang Chunfeng
National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing 210093, China.
College of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China.
J Phys Chem Lett. 2023 Aug 24;14(33):7498-7506. doi: 10.1021/acs.jpclett.3c01861. Epub 2023 Aug 15.
For over two decades, most high-performance organic photovoltaics (OPVs) have been made with donor:acceptor bulk heterojunctions with domain sizes limited by exciton diffusion, where charge separation mostly takes place through the dissociation of the interfacial charge-transfer (xCT) excitons. Recently, nonfullerene acceptor (NFA)-based OPVs have shown excellent compatibility to device structures with large domains in active layers. However, it remains elusive how the excitations that are distant from the interfaces are converted into free charges. Here, we report the identification of a new charge separation channel in model copolymer/NFA blends mediated by intra-moiety delocalized excitations in both planar heterojunctions and donor-enriched bulk heterojunctions. The delocalized excitations induced by interchromophore electronic interactions in copolymer donors mediate the long-range charge separation and dissociate into free charges without forming the bound xCT states first, releasing the constraints associated with the short exciton diffusion length in organic materials. The long-range charge separation mechanism uncovered in this work, in cooperation with the short-range xCT-mediated pathway, holds the potential to further optimize OPVs with diverse device structures.
二十多年来，大多数高性能有机光伏电池（OPV）都是由供体：受体体相异质结制成的，其畴尺寸受激子扩散限制，电荷分离主要通过界面电荷转移（xCT）激子的解离发生。最近，基于非富勒烯受体（NFA）的OPV对有源层中具有大畴的器件结构表现出优异的兼容性。然而，远离界面的激发如何转化为自由电荷仍然不清楚。在这里，我们报告了在模型共聚物/NFA共混物中鉴定出一种新的电荷分离通道，该通道由平面异质结和供体富集体相异质结中部分内离域激发介导。共聚物供体中发色团间电子相互作用诱导的离域激发介导远程电荷分离，并解离为自由电荷，而不首先形成束缚的xCT态，从而释放了与有机材料中短激子扩散长度相关的限制。这项工作中发现的远程电荷分离机制，与短程xCT介导的途径相结合，有潜力进一步优化具有不同器件结构的OPV。
