Materials World Network: Understanding the Design and Characterization of Air-Stable N-Type Charge Transfer Dopants for Organic Electronics

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TECHNICAL SUMMARYCharge transfer doping is crucial in enabling highly efficient organic light emitting diodes and organic solar cells, and is needed for controlling the electrical characteristics of organic field effect transistors. Whereas the development of p-type dopants is well advanced, there is still a lack of effective air-stable solution processabile n-type dopants, due to limited knowledge on the detailed doping mechanisms. To address this gap, this Materials World Network project, supported by the Solid State and Materials Chemistry program and the Office of Special Programs, Division of Materials Research, aims at a) understanding the design rules for air-stable n-dopants based on a promising class of dopants with (1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl (DMBI) as the model system and b) understanding the detailed doping mechanisms of n-type doping. The three groups involved in the project have a unique combination of complementary expertise. The Bao group will synthesize DMBI dopants with systematically varied energy levels and substituents for better miscibility with the matrix to aid the understanding of doping mechanisms. The chemical process of doping will be investigated with UV-vis-NIR and electron paramagnetic resonance. The morphology of doped layers will be studied by atomic force microscopy, various X-ray techniques and nanoSIMS. The Leo group in Germany will study the physical mechanisms of doping by impedance spectroscopy, ultraviolet photoelectron spectroscopy, the Seebeck measurement, and modeling of the charge transport characteristic by a master equation model. The air-stability will be tested and the dopants will be used in state-of-the art organic devices such as light emitting diodes, solar cells, or transistors. Finally, the Cuniberti group in Germany will study the doping effect on a single molecular level by high resolution scanning tunneling microscopy and will model the doping process by ab initio calculations based on density functional theory. NON-TECHNICAL SUMMARY: Charge transfer doping is crucial in enabling highly efficient displays, solid-state lighting, organic solar cells, and is needed for controlling the electrical characteristics of organic field effect transistors. Whereas the development of p-type dopants is well advanced, there is still a lack of effective air-stable solution processabile n-type dopants, due to limited knowledge on the detailed doping mechanisms. This Materials World Network project will advance the understanding of the chemistry and physics of doping through an international co-operation across the disciplines of chemistry/ chemical engineering, fundamental physics and theory. These findings will lead to better understanding of design rules for stable and efficient n-dopants and more efficient devices. This project will train students and postdocs with a solid fundamental understanding as well as a global experience. This project will help to foster economic growth by furthering the field of organic electronics and the associated industry. This project will train students with exposure to interdisciplinary research and diverse cultures. Bao will work closely with Stanford NSF centers and Office of Science Outreach to reach out to a broad population ranging from K-12, community college, undergraduate, and graduate students, as well as prepare the teachers of tomorrow for new areas of science and technology.