High Polaron Yield p-Doping with an Ammoniumyl Radical Cation Oxidant for Organic Thin-Film Transistors

Doping is a crucial strategy for effectively modulating the charge transport properties of organic semiconductors and thus the performance of the resulting organic optoelectronic devices. In this study, we report an ammoniumyl radical cation oxidant, tris(4-bromophenyl)ammoniumyl hexachloroantimonate (magic blue, MB), for tuning the performance of diketopyrrolopyrrole polymer (TDPP-Se)-based organic thin-film transistors (OTFTs). In comparison to the classical dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), MB oxidizes TDPP-Se into nonradical bipolarons at a higher polaron yield of ∼100% and lower energy levels to trap unwanted minority carriers. As a result, the MB-doped system overcomes the leveling up of off-current prevalently observed in doped OTFTs. In addition, MB is compatible with the host semiconductor and enhances the crystallization of the polymer, facilitating the formation of ordered films with a reduced trap density. Following optimization of the doping ratio, bar-coated OTFTs achieve a maximum mobility of 7.59 cm2 V–1 s–1, with the threshold voltage reduced to −2 V and without sacrificing the on/off ratio. These results demonstrate the potential of the strong radical oxidant for high polaron yield p-doping in organic optoelectronic devices.