OLEDs without Iridium. 100% efficient triplet harvesting by Thermally Activated Delayed Fluorescence.

能源议程要求更高效的显示和照明技术来满足英国政府的目标。Monkman， Dias和Bryce教授提出了一种仅使用有机荧光发射器的高效有机led （oled）的新范例，而不是目前非常流行的基于Ir的有机金属磷光发射器。磷光发射器有很大的局限性。蓝光磷光复合物的稳定性差，寿命短，而且它们还不能产生显示和固态照明应用所需的深蓝色发光。此外，它们大多含有Ir作为核心重金属，这是地球上第四大最稀缺的元素，因此将大量生产的照明技术建立在如此稀缺的资源上是非常危险的。我们的新器件将有有机内部电荷转移（ICT）分子作为其发射器。ICT分子的激发态具有很强的电荷转移特性，其电子交换能极小，导致单线态和三重态能量几乎相等。这意味着三重态CT态可以有效地（热）逆转系统间交叉回到单重态歧管，从而提供了一种“收获”OLED器件中由电荷重组形成的三重态的方法，即它们可以与最好的磷光发射器一样有效。因此，ICT发射体可以结合磷光发射体最理想的特性，即100%三重态收获，并具有荧光发射体长期稳定性的额外好处。这是显示器和照明制造商都需要的，但在蓝色光谱区域还没有。替换磷光蓝光发射器尤为重要，因为它们在设备制造中使用的真空沉积过程中会发生化学降解；它们的工作寿命短，不会发出深蓝色的光，而这对于高质量的显示器和照明来说都是必不可少的。到目前为止，我们的初步研究表明，TADF分子可以以高达100%的效率收获三胞胎，并且在固体状态下，在宿主中分离TADF分子为非常有效的TADF发射提供了理想的条件。因此，这些材料非常适合OLED应用。此外，我们在日本的合作者已经证明了简单的单色TADF oled具有高达85%的内部量子效率。TADF发射器看起来很好地为Ir荧光粉提供了一个独特的挑战。在这个项目中，我们将对ICT分子进行详细的光物理研究，这些分子在固态下显示出非常有效的TADF。我们将开发模型来充分理解这种三重态收获方法和结构-性质关系，以优化设计和合成覆盖整个可见光谱的新型高效TADF发射器家族。oled将由这些新材料制成并充分表征。最后，将评估结合两个或多个TADF发射器的器件架构，以确定在简单器件结构中从TADF发射器产生白色发射的最佳途径。

The energy agenda demands more efficient display and lighting technologies to meet the UK government's targets. Professors Monkman, Dias and Bryce propose a new paradigm for highly efficient organic LEDs (OLEDs) using only organic fluorescent emitters, rather than Ir based organometallic phosphorescent emitters that are currently very fashionable. Phosphorescent emitters have major limitations. Blue-emitting phosphorescent complexes especially suffer from poor stability and short lifetimes, and they have not yet produced the deep-blue emission required for both display and solid-state lighting applications. Further, they mostly contain Ir as the core heavy metal, this is the fourth most scarce element on the planet, and so basing high volume mass produced lighting technology on such a scarce resource is highly risky. Our new devices will have as their emitters organic internal charge transfer (ICT) molecules. The excited states of ICT molecules have strong charge transfer character which can have vanishingly small electron exchange energies resulting in nearly equivalent singlet and triplet energies. This means that it is efficient for triplet CT states to (thermally) reverse intersystem crossing back to the singlet manifold, thereby giving a method of 'harvesting' up to 100% of triplet states formed by charge recombination in an OLED device, i.e. they can be as efficient as the best phosphorescent emitter. Thus ICT emitters can combine the most desirable properties of phosphorescent emitters, namely 100% triplet harvesting, with the added benefit of the long term stability of a fluorescent emitter. This is what both display and lighting manufactures demand but as yet do not have in the blue spectral region. It is particularly important to replace phosphorescent blue emitters, as they chemically degrade during the vacuum deposition process used in device fabrication; they have short working lifetimes and do not emit deep-blue light which is essential for both high quality displays and lighting. Our Initial studies have so far demonstrated that TADF molecules can harvest triplets with up to 100% efficiency, and also in the solid state, isolation of TADF molecules in a host affords ideal conditions for very efficient TADF emission. Thus these materials are perfectly suited for OLED applications. Furthermore, our collaborators in Japan have demonstrated simple monochrome TADF OLEDs having up to 85% internal quantum efficiency. TADF emitters are looking well set to provide a unique challenge to Ir phosphors.During this project we shall undertake detail photophysical investigations of ICT molecules that show very efficient TADF in the solid state. We will develop models to understand fully this triplet harvesting method and structure-property relationships to optimise the design and synthesis of new families of efficient TADF emitters covering the whole visible spectrum. OLEDs will be fabricated from these new materials and fully characterized. Finally, device architectures that combine two or more TADF emitters will be evaluated to determine the best routes to producing white emission from TADF emitters in simple device structures.