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

• Applicant: Professorin Dr. Anna Köhler, since 4/2019
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392306670

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.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Cooperation Partner: Professorin Dr. Youtian Tao
• Ehemaliger Antragsteller: Professor Dr. Sven Hüttner, until 3/2019