Electrotuneable Radical Polymers for Thin-Film Electronic Device Applications

Polyradicals, organic polymers in which each repeating sub-unit contains a stable radical with an unpaired spin, are establishing themselves as unique alternatives to state-of-the-art conducting polymers for a variety of applications. A decisive advantage of polyradicals rests on their charge tunability and switchable transport properties. Current interests in polyradicals have been focused on batteries and resistive memory devices. Polyradical doping has remained a challenge, however, notwithstanding recent developments. Due to doping issues, single-component polyradical organic field-effect transistors (OFETs), a vital milestone in polyradical electronics, have not yet been achieved. Here, we demonstrate that an OFET architecture with source-drain contacts sandwiching the polyradical active layer led to on/off ratios >103 in what are the first p-type polyradical-FETs (PR-FETs) reported so far. These OFETs are based on a 6-oxoverdazyl polyradical with no impurity doping, in which hole injection occurs due to tunable charge states at the polyradical/source interface. By introducing the new concept of contact-doping, our work provides a route for translating single-component polyradical thin films into OFETs, the fundamental building blocks of organic electronics. Because of the switchable transport properties of 6-oxoverdazyl polyradicals, our PR-FETs could be used to implement the first organic mem-transistors reported to date.