Controlled doping of organic semiconductors and 2d materials with molecular reductants and oxidants
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New air-stable dimeric n-dopants are synthesized and studied in detail with respect to the kinetics of both their redox reaction in solution with and their doping in the solid-state of various organic semiconductor acceptors. Detailed mechanistic studies are necessary to recognize the strengths and limitations of existing dimers to inform future dopant design. The newly synthesized n-dopants together with other redox-active n- and p-dopants are then used to surface modify mono- and multi-layer graphene, which shows a large decrease in the sheet resistance and tunable work function shifts. A subset of these molecules is applied to MoS2 and WSe2 to realize controllable n- and p-doping, respectively, to improve their electrical properties. Other experimental techniques, especially UPS and XPS, are coupled with the electrical measurements to give information about work function shifts, surface coverage, charge transfer efficiency, and etc. Finally, organic diodes, solar cells, and field-effect transistors with doped graphene electrodes were fabricated, where the work function engineering of graphene electrodes via doping proved to be important in reducing the carrier-injection barriers.