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

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Charge 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 project 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 UVvis- 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 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 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.