Zhang Xinping, Yang Qiaohui, Fu Yulan, Zhang Yiwei
Institute of Information Photonics Technology, Beijing University of Technology, Beijing 100124, People's Republic of China.
ACS Macro Lett. 2021 Oct 19;10(10):1236-1242. doi: 10.1021/acsmacrolett.1c00501. Epub 2021 Sep 30.
Charge-transfer states have been observed extensively in heterojunctions of organic semiconductors, which are also referred to as exciplexes in polymer blends. Such mechanisms have been well understood in the conventional material systems. However, electromer states may be produced only in some polymeric molecules with folded chains. We report here the interaction between exciplex and electromer states, which facilitates the formation of a new electrically excited state that we define as a secondary exciplex. This is an indirect process understood as an electromer-mediated heterojunction. We discovered such an optoelectronic mechanism in the blend film of poly(9,9'-dioctylfluorene--bis-,'-(4-butylphenyl)-bis-,'-pheny-l,4-phenylene-diamine) (PFB) and poly[(9,9-dioctylfluorenyl-2,7-diyl)--(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT). Four emission bands can be resolved from the electroluminescence spectrum, including those based on the excitons, the electromers, and the primary and secondary exciplexes. The whole electroluminescence spectrum thus extends from the green (500 nm) to the near-infrared (900 nm) with a full bandwidth of 400 nm. These new discoveries with the conventional light-emitting polymers are important not only for polymeric optoelectronics, but also for the development of broadband light-emitting devices.
电荷转移态在有机半导体异质结中已被广泛观察到，在聚合物共混物中也被称为激基复合物。这种机制在传统材料体系中已得到很好的理解。然而，电异构体态可能只在一些具有折叠链的聚合物分子中产生。我们在此报告激基复合物态与电异构体态之间的相互作用，这种相互作用促进了一种新的电激发态的形成，我们将其定义为次级激基复合物。这是一个被理解为电异构体介导的异质结的间接过程。我们在聚（9,9'-二辛基芴 - 双 - ，' - （4 - 丁基苯基） - 双 - ，' - 苯基 - 1,4 - 亚苯基二胺）（PFB）和聚[（9,9 - 二辛基芴基 - 2,7 - 二基） - （苯并[2,1,3]噻二唑 - 4,8 - 二基）]（F8BT）的共混薄膜中发现了这种光电机制。从电致发光光谱中可以分辨出四个发射带，包括基于激子、电异构体以及初级和次级激基复合物的发射带。因此，整个电致发光光谱从绿色（500 nm）延伸到近红外（900 nm），全带宽为400 nm。这些与传统发光聚合物相关的新发现不仅对聚合物光电子学很重要，而且对宽带发光器件的开发也很重要。
