Science has always been full of surprises, and organic light-emitting diodes (OLEDs) are no exception. What exasperates scientists today may entice society tomorrow. The world has witnessed a revolution in display technology in the past two decades. In this period, the displays with bulky and heavy cathode ray tubes were transformed into ultra-slim OLED display panels. Commercialization of any new technology requires a delicate balance between device efficiency and manufacturing cost. OLEDs are still costlier than the popular liquid crystal-based displays (LCDs) because of their higher production cost. However, OLEDs are gradually replacing LCDs. The current OLED-based devices mainly utilize phosphorescent emitters that exhibit some cost and environmental concerns. Therefore, developing OLEDs with only organic components has remained the primary goal in OLED research. The discovery of thermally activated delayed fluorescence (TADF) OLEDs presents a major impetus in this area. Organic TADF molecules can be feasibly realized by manipulating the intramolecular or intermolecular charge transfer between electron-donor and electron-acceptor. The current article discusses the exciplexes formed by intermolecular charge transfer and their versatile applications in OLEDs. In the past OLED research, scientists were often bothered by the red-shifted electroluminescence band along with the desired excitonic emission, which was later identified as the exciplex emission. Exciplexes are virtual emitters that exist only in the electronically excited states. They are formed when electron-rich and -deficient compounds with appropriate frontier molecular orbitals come close enough for orbital participation, one of them being in the excited state. Given the lack of sophisticated characterization technology, exciplex emission was not fully understood back then and was considered a defect in device design. However, some were also inquisitive about the possibilities. The importance of exciplexes in OLEDs was finally recognized in the early 2010s when scientists were elated about the enormous opportunities they could offer. These emitters can be easily generated in a blend of donor and acceptor molecules without the need for complicated syntheses. They also exhibit excellent TADF emission. The researchers were exuberant about the discovery, and a slew of publications have followed the original article published by Adachi and coworkers in 2012. Exciplexes can be applied as emitters and hosts in OLEDs. The efficiency of the relevant devices gradually approaches the phosphorescent OLEDs. In the present article, we have systematically reviewed this success story, reminding the OLED community of the transformation of annoyance into ecstasy, to assist this community in developing high-performing devices based on the data accumulated herewith.

科学向来充满惊喜，有机发光二极管（OLED）也不例外。今天激怒科学家的东西可能会吸引明天的社会。在过去的二十年里，世界见证了显示技术的革命。在此期间，具有笨重的阴极射线管的显示器被转变为超薄的 OLED 显示面板。任何新技术的商业化都需要在设备效率和制造成本之间取得微妙的平衡。由于生产成本较高，OLED 仍然比流行的基于液晶的显示器 (LCD) 更昂贵。然而，OLED正在逐渐取代LCD。当前基于 OLED 的设备主要使用磷光发射器，这些发射器表现出一些成本和环境问题。所以，开发仅含有机成分的 OLED 一直是 OLED 研究的主要目标。热激活延迟荧光 (TADF) OLED 的发现是该领域的主要推动力。有机TADF分子可以通过操纵电子供体和电子受体之间的分子内或分子间电荷转移来实现。目前的文章讨论了由分子间电荷转移形成的激态复合物及其在 OLED 中的多种应用。在过去的 OLED 研究中，科学家们经常被红移的电致发光带以及所需的激子发射所困扰，后者后来被确定为激子发射。激发复合体是仅存在于电子激发态的虚拟发射体。它们是在具有适当前沿分子轨道的富电子和缺电子化合物足够接近轨道参与时形成的，其中一种处于激发态。由于缺乏复杂的表征技术，当时还没有完全理解激基复合物发射，并被认为是器件设计中的缺陷。然而，有些人也对这些可能性感到好奇。2010 年代初，当科学家们对它们可以提供的巨大机会感到欣喜若狂时，OLED 中激基复合物的重要性终于得到了认可。这些发射器可以很容易地在供体和受体分子的混合物中生成，而无需复杂的合成。它们还表现出出色的 TADF 排放。研究人员对这一发现充满热情，在 Adachi 及其同事在 2012 年发表的原始文章之后，大量出版物也相继发表。激化复合物可用作 OLED 中的发射器和主体。相关器件的效率逐渐接近磷光OLED。在本文中，我们系统地回顾了这个成功案例，提醒 OLED 社区将烦恼转化为狂喜，以帮助该社区根据所积累的数据开发高性能设备。