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Substituent-Controlled Reversible Switching of Charge-Injection-Barrier Heights at Metal/Organic-Semiconductor Contacts Modified with Disordered Molecular Monolayers

Electrically stimulated switching of a charge injection barrier at the interface between an organic semiconductor and an electrode modified with a disordered monolayer (DM) is studied by using various benzenethiol derivatives as DM molecules. The switching behavior is induced by a structural change in the DM molecules, and is manifested as a reversible inversion of the polarity of DM-modified Au electrode/rubrene/DM-modified Au electrode diodes. The switching direction is found to be dominantly determined by the push-back effect of the thiol bonding group, while the terminal group modulates the switching strength. A device with 1,2-benzenedithiol DMs exhibited the highest switching ratios of 20, 100, and 1000 for the switching voltages of 3, 5, and 7 V, respectively. A variation in the tilt angle of benzenethiol DMs owing to the application of 7 V is estimated to be smaller than 23.6 degrees by model calculations. This study offers an understanding for obtaining highly stable operations of organic electronic devices, especially with molecular modification layers.