High mobility field-effect transistors produced by direct growth of C70 single crystals from a solution

Abstract

Fullerene C₇₀ crystals are n-type semiconductor materials that are used in organic field-effect transistors (OFETs). However, research on C₇₀ FETs has so far been limited to low electron mobilities below ∼10⁻² cm² V⁻¹ s⁻¹. To achieve higher mobilities, it is essential to enhance the electrical contact between C₇₀ crystals and the FET substrate with electrodes, as well as to grow high-quality crystals. In this study, high-mobility FETs were produced by directly growing C₇₀ crystals from a C₇₀ saturated m-xylene solution. Good electrical contact between the C₇₀ crystals and FET substrates with electrodes is realized in a bottom-gated bottom-contact FET configuration. The resulting rhombohedral shaped C₇₀ crystals exhibited solvated hexagonal structures with lattice parameters of a = 50.52 Å and c = 24.70 Å. These directly grown C₇₀ crystal FETs exhibited typical n-type output and transfer characteristics. The electron mobility improved after annealing at 100 °C in a vacuum, which is probably due to the desorption of H₂O and O₂ in the crystals, although the solvation in the crystals was preserved. The solvated C₇₀ crystal FETs achieved a high electron mobility of 1.14 cm² V⁻¹ s⁻¹ which is an improvement of more than two orders of magnitude relative to previously documented C₇₀ FETs, demonstrating the potential of C₇₀ crystals for use in electronic devices.