Triplet concepts for organic photovoltaics: new materials, devices and mechanisms

这项合作研究旨在探索三重态发挥关键作用的高效有机光伏材料和器件。在目前的现有技术的有机光致发光三重态和电荷转移三重态很少被认为是提高器件效率。大多数本体异质结太阳能电池依赖于单重激发态的光生，其在供体/受体界面处形成单重电荷转移态并且可以分离成自由电荷。限制因素例如是小的激子扩散长度或在施主-受主界面处的进一步复合过程。为了解决这些因素，本项目的目的是在利用三重态机制及其在高效光化学中的应用方面获得基本的理解。合成新型三重态活性组分和高效共轭有机光伏材料。后者可以提供宽且强的光吸收、合适的最高占据分子轨道（HOMO）/最低未占据分子轨道（LUMO）能级和高电荷迁移率。此外，这些材料将被用来详细研究利用三重态的不同概念的量子物理学。这些包括具有重金属络合掺杂剂的供体/受体共混物以及携带掺入的重金属络合物以直接进入三重态的供体材料。例如，如果电荷转移三重态可以被有效地访问并且各个供体材料的三重态能级足够高，则应当减慢或避免复合，并且因此电荷产生增强。南京理工大学的陶教授将开发、理论计算和合成新材料，拜罗伊特大学的Huettner教授将研究结构、纳米形态和光电性能，为两个研究小组提供材料合成和器件物理的互补优势。通过这项合作研究，我们希望为三胞胎在有机光化学中的作用这一长期存在的问题提供新的解决方案。此外，它有望在有机太阳能电池领域发现新的现象，提出新的问题，并为新的光伏材料的进一步设计规则提供指导。

This collaborative research is aimed to explore high efficiency organic photovoltaic materials and devices where triplet states play a crucial role. In current state-of-the-art organic photovoltaics triplet states and charge transfer triplet states have only rarely been considered to improve device efficiencies. Most bulk heterojunction solar cells rely on the photogeneration of singlet excited states, which form singlet charge transfer states at the donor/acceptor interface and may separate into free charges. Limiting factors are for example the small exciton diffusion length or further recombination processes at the donor-acceptor interface. In order to address those factors, this project aims to gain a fundamental understanding in the utilization of triplet mechanisms and their application in high efficiency photovoltaics. Novel triplet active components and high efficiency conjugated organic photovoltaic materials will be synthesized. The latter may provide a broad and strong optical absorption, suitable highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy levels and high charge mobility. Furthermore, these materials will be used to investigate the photophysics of different concepts that utilize triplet states in detail. These include donor/acceptor blends with heavy metal complexed dopants as well as donor materials that carry incorporated heavy metal complexes to directly access triplet states. For example, recombination should be slowed down or avoided and hence charge generation enhanced, if the charge transfer triplet states can be efficiently accessed and triplet levels of respective donor materials are sufficiently high. New materials will be developed, theoretical calculated and synthesized by Prof. Tao, Nanjing Tech and the structural, nanomorphological and opto-electronic properties will be investigated by Prof. Huettner, Universtät Bayreuth, providing complementary advantages of materials synthesis and device physics between the two research groups. With this collaborative research we hope to shine new light into long asked questions of the role of triplets in organic photovoltaics. Furthermore, it is expected to discover new phenomena as well as raise new questions in the field of organic solar cells and provide guidelines for the further design rules of new photovoltaic materials.