TADF Emitters for OLEDs

照明占世界电力需求的近20%。广泛采用节能照明将对能源消耗和环境产生深远的积极影响。此外，在发展中国家，改善照明将增加经济产出。有机半导体是用于照明应用的有吸引力的材料，因为可以调节它们的性质（例如发光的颜色）并通过简单的方法从溶液中存款它们。这意味着它们具有廉价制造大面积光源的潜力，并且这种光源具有柔性或适形的可能性。光发射过程涉及注入相反的电荷，这些电荷联合收割机形成被称为单重态和三重态的激发态。在大多数材料中，三联体不发光，但为了高效率，需要收集三联体以有助于发光。现有技术的照明装置（有机发光二极管，OLED）采用铱和其它金属络合物磷光体的使用。这些金属的稀有性及其相关成本排除了它们在廉价照明设备中的使用。在这个项目中，我们建议探索热激活延迟荧光（TADF）发射器，这些发射器提供了一个诱人的解决方案，因为这些材料是基于小分子有机化合物，即由非常丰富的材料制成。TADF发射体依赖于分子设计，其中单重态和三重态能级足够接近，使得三重态到发光单重态的转换是有效的，从而导致高效的发光器件。TADF发光材料的廉价起始材料和相对低的合成成本以及与昂贵的金属配合物相当的光电性能使得这种下一代发光材料非常有前途。（3）低成本EL器件的制作。对于（1）和（2），我们将设计和评估应对这些挑战的材料，并通过详细的物理和光电测量将材料的特性与其结构联系起来。迄今为止，大多数关于TADF材料的工作都集中在蒸发材料上。相反，我们将开发可以从溶液中加工的材料，以解决简单制造的挑战（3），从而实现这些低成本但高效的发射器的全部好处。

Lighting accounts for almost 20% of world electricity demand. Widescale adoption of energy efficient lighting would have a profound positive effect on energy consumption and the environment. In addition, in the developing world improved lighting would increase economic output. Organic semiconductors are attractive materials for lighting applications because of the scope to tune their properties (such as colour of light emission) and deposit them by simple processes from solution. This means they have the potential for large area light source to be made inexpensively, and the possibility of such light sources being flexible or conformable. The light emission process involves injecting opposite charges which combine to form excited states called singlets and triplets. In most materials triplets do not emit light, but for high efficiency the triplets need to be harvested to contribute to light emission. The present state-of-the-art lighting devices (organic light-emitting diodes, OLEDs) employ the use of iridium and other metal complex phosphors. The rarity of these metals and their associated cost precludes their use in inexpensive lighting devices. In this project we propose to explore thermally activated delayed fluorescence (TADF) emitters which offer a tantalizing solution as these materials are based on small molecule organic compounds i.e. are made from very abundant materials. TADF emitters rely on a molecular design where the singlet and triplet energy levels are close enough together that conversion of triplets to light-emitting singlets is efficient, thereby leading to highly efficient light-emitting devices. The inexpensive starting materials and relatively low-cost synthesis coupled with comparable optoelectronic properties to the exepnsive metal complexes makes this next-generation of emitters very promising.In our proposal we address grand challenges in the development of TADF emitters: (1) the development of a bright and stable deep blue emitter; (2) the improvement of high efficiency red emitters based on organic compounds; (3) the fabrication of low cost EL devices. For (1) and (2) we will design and evaluate materials that address these challenges, guided by detailed photophysical and optoelectronic measurements to relate the properties of the materials to their structure. Most work on TADF materials to date has focused on evaporated materials. Instead we will develop materials that can be processed from solution to address challenge (3) of simple fabrication to enable the full benefit of these low cost but efficient emitters to be realised.