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

这项合作研究旨在探索高效有机光伏材料和器件，其中三重态起着至关重要的作用。在目前最先进的有机光伏中，三重态和电荷转移三重态很少被认为可以提高器件效率。大多数体异质结太阳能电池依赖于单线态激发态的光产生，单线态激发态在供体/受体界面形成单线态电荷转移态，并可能分离成自由电荷。例如，限制因素是小激子扩散长度或进一步的重组过程在供体-受体界面。为了解决这些因素，本项目旨在对三重态机制的利用及其在高效光伏发电中的应用有一个基本的了解。将合成新型三联体活性组分和高效共轭有机光伏材料。后者可以提供广泛而强的光吸收，合适的最高已占据分子轨道(HOMO)/最低未占据分子轨道（LUMO）能级和高电荷迁移率。此外，这些材料将用于详细研究利用三重态的不同概念的光物理学。这些包括与重金属络合掺杂剂的供体/受体共混物，以及携带掺入重金属络合物以直接进入三重态的供体材料。例如，如果可以有效地进入电荷转移三重态，并且各自供体材料的三重态能级足够高，则应减缓或避免重组，从而增强电荷产生。南京工业大学陶教授将负责新材料的开发、理论计算和合成，Huettner教授（Universtät Bayreuth）将研究新材料的结构、纳米形态和光电性能，为两个研究小组在材料合成和器件物理方面提供互补优势。通过这项合作研究，我们希望为三联体在有机光伏中的作用这一长期被问到的问题带来新的曙光。并有望在有机太阳能电池领域发现新现象，提出新问题，为进一步制定新型光伏材料的设计规则提供指导。

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.