Radical polymers improve the metal-semiconductor interface in organic field-effect transistors

• Radical polymer interlayers improve the performance of field-effect transistors.
• The modification of the organic-metal interface reduced contact resistance.
• This led to improved field-effect mobility values for pentacene-based devices.
• The ON/OFF ratios of the devices were increased by 3 orders of magnitude.
• The layer improved the electrochemical and morphological aspects at the interface.

Modifying the organic-metal interface in organic field-effect transistors (OFETs) is a critical means by which to improve device performance; however, to date, all of the interfacial modifying layers utilized in these systems have been closed-shell in nature. Here, we introduce open-shell oxidation-reduction-active (redox-active) macromolecules, namely radical polymers, in order to serve as interfacial modifiers in pentacene-based OFETs. Through careful selection of the chemistry of the specific radical polymer, poly(2,2,6,6-tetramethylpiperidine-1-oxyl methacrylate) (PTMA), the charge transport energy level of the interfacial modifying layer was tuned to provide facile charge injection and extraction between the pentacene active layer and the gold source and drain electrodes of the OFET. The inclusion of this radical polymer interlayer, which was deposited in through straightforward inkjet printing, led to bottom-contact, bottom-gate OFETs with significantly increased mobility and ON/OFF current ratios relative to OFETs without the PTMA interlayer. The underlying mechanism for this improvement in device performance is explained in terms of the charge transport capability at the organic-metal interface and with respect to the pentacene grain growth on the radical polymer. Thus, this effort presents a new, open-shell-based class of materials for interfacial modifying materials, and describes the underlying physics behind the practical operation of these materials.

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