Organic field-effect transistors (OFETs) with a top-contact structure were fabricated by applying deoxyribonucleic acid (DNA) as a hole injection layer between organic semiconductor and electrousing a simple spray-coating process. Compared with that of the bare OFET, the OFET incorporated with a DNA hole injection layer exhibited a significant enhancement of field-effect mobility from 0.02 to 0.104 cm2 V−1 s−1. By analyzing the electrical characteristics of these OFETs and the surface morphology of the pentacene film, the results showed that the dipole formation effect brought by the DNA interlayer effectively reduced the contact resistance between the gold electrodes and the pentacene film. Consequently, improved hole injection was obtained along with the enhanced electrical characteristics. Moreover, DNA is soluble in aqueous solvent only and compared to spin-coating process, spray-coating process is beneficial to film formation of DNA aqueous solution with high viscosity and thus make DNA interlayer well incorporated in OFET device. In order to confirm the performance enhancement effect brought by DNA interlayer, OFETs based on another p-type organic semiconductor of α-hexathiophene and the OFETs based on silver electrodes were also investigated. The results showed that the α-hexathiophene based OFETs also exhibited significant performance improvement and the large injection barrier between silver electrodes and the pentacene organic semiconductor was significantly reduced by DNA interlayer. In addition, among the four kinds of base-pairs in DNA molecule, the guanine base-pair exhibits the lowest oxidation potential owing to its peculiar sequence of H-bond donor or acceptor groups. Therefore, the guanine base-pair was selected to be further analyzed and the results confirmed the existence of the dipole formation effect in DNA molecule. Moreover, in the case of organic electronics, environmental stability is another crucial feature. The main discrepancy of pentacene film after exposure to air is the generation of the deep trap states. When the OFET is exposed to air, deep trap states which result from the absorption of H2O and other molecules lead to a degradation in performance. When a DNA hole injection layer was introduced, the surface of pentacene film was protected from direct contact with ambient conditions and the degradation of the device was thus slowed down.
University of Electronic Science and Technology of China
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