Polarity and Air-Stability Transitions in Field-Effect Transistors Based on Fullerenes with Different Solubilizing Groups

A series of o-xylene and indene fullerene derivatives with varying frontier molecular orbital energy levels were utilized for assessing the impact of the number of solubilizing groups on the electrical performance of fullerene-based organic-field-effect transistors (OFETs). The charge-carrier polarity was found to be strongly dependent upon the energy levels of fullerene derivatives. The o-xylene C₆₀ monoadduct (OXCMA) and indene C₆₀ monoadduct (ICMA) exhibited unipolar n-channel behaviors with high electron mobilities, whereas the bis- and trisadducts of indene and o-xylene C₆₀ derivatives showed ambipolar charge transport. The OXCMA OFETs fabricated by solution shearing and molecular n-type doping showed an electron mobility of up to 2.28 cm² V^–1 s^–1, which is one of the highest electron mobilities obtained from solution-processed fullerene thin-film devices. Our findings systematically demonstrate the relationship between the energy level and charge-carrier polarity and provide insight into molecular design and processing strategies toward high-performance fullerene-based OFETs.