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，以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体而不是目前非常流行的Ir基有机金属磷光发射体的高效有机LED（OLED）的新范例。磷光体发射体有很大的局限性。发蓝光的磷光配合物尤其受到稳定性差和寿命短的困扰，并且它们尚未产生显示器和固态照明应用所需的深蓝色发射。此外，它们大多含有Ir作为核心重金属，这是地球上第四大稀缺元素，因此将大批量生产的照明技术基于这种稀缺资源是高度风险的。我们的新器件将以有机内部电荷转移（ICT）分子作为发射体。ICT分子的激发态具有很强的电荷转移特性，其电子交换能非常小，导致单重态和三重态能量几乎相等。这意味着三重态CT有效地（热）反转系统间穿越回到单线态歧管，从而给出了一种在OLED器件中“收获”高达100%的通过电荷复合形成的三重态的方法，即它们可以与最好的磷光发射体一样有效。因此，ICT发射体可以将磷光发射体的最期望的性质（即100%三重态收获）与荧光发射体的长期稳定性的附加益处结合联合收割机。这是显示器和照明制造商的需求，但在蓝色光谱区域还没有。更换蓝色磷光发光体尤为重要，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，并且不会发出高质量显示器和照明所必需的深蓝色光。到目前为止，我们的初步研究已经证明，TADF分子可以以高达100%的效率收获三联体，并且在固态下，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展示了简单的单色TADF OLED，其内部量子效率高达85%。TADF发射器看起来很好地设置为提供一个独特的挑战，铱磷光体。在这个项目中，我们将进行详细的ICT分子的物理研究，显示非常有效的TADF在固态。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，以优化覆盖整个可见光谱的高效TADF发射器的新家族的设计和合成。OLED将由这些新材料制造并充分表征。最后，将评估联合收割机组合两个或更多个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路线。

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.