Tunable Frohlich Polarons in Organic Single-Crystal Transistors

Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
Nature Materials (Impact Factor: 36.5). 01/2007; 5(12):982-6. DOI: 10.1038/nmat1774
Source: PubMed


In organic field-effect transistors (FETs), charges move near the surface of an organic semiconductor, at the interface with a dielectric. In the past, the nature of the microscopic motion of charge carriers--which determines the device performance--has been related to the quality of the organic semiconductor. Recently, it was discovered that the nearby dielectric also has an unexpectedly strong influence. The mechanisms responsible for this influence are not understood. To investigate these mechanisms, we have studied transport through organic single-crystal FETs with different gate insulators. We find that the temperature dependence of the mobility evolves from metallic-like to insulating-like with increasing dielectric constant of the insulator. The phenomenon is accounted for by a two-dimensional Fröhlich polaron model that quantitatively describes our observations and shows that increasing the dielectric polarizability results in a crossover from the weak to the strong polaronic coupling regime. This represents a considerable step forward in our understanding of transport through organic transistors, and identifies a microscopic physical process with a large influence on device performance.

  • Source
    • "Their best construction was based on poly(chloro-p-xylylene) dielectric (parylene C), and its performance, namely that of hole mobility μ FE = 0.81 cm 2 /Vs and I on/off = 1.4 × 10 6 , is still considered very good today. Then, in the work by Hulea et al. [17], OFETs based on the single crystals of rubrene with different gate dielectrics were investigated and it was found, that an application of parylene resulted in the highest charge carrier mobility, close to that of 10 cm 2 /Vs. Different mechanisms, responsible for such an effect were discussed in a review paper by Ortiz et al. [18] Recently, a report on flexible picene OTFTs built on polyethylene terephthalate substrate and equipped with parylene C gate dielectric was published by Kawasaki et al. [19]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Along with the technology of microscopic electromechanical systems and that of brain–machine interface, the area of organic electronics presents a major development direction of high-tech applications of parylene coatings. Within this area, a fabrication of organic field-effect transistors (OFETs), where parylene C is applied as a gate di-electric, makes the most common use of these materials. The main advantage of parylene coatings in the OFET technology is their very high purity. Depending on a transistor design, films of parylene C may play a role of the gate dielectric material, that of a protective insulator coating, and/or that of a device substrate. The work presents a number of applications of parylene C in different OFET devices, namely in organic thin film transistors (OTFTs) and organic single-crystal transistors developed by the authors. A combination of zone-cast films of active materials, both n-type and p-type, with parylene C gate dielectric makes a principal design of the OTFTs. In this group, the best performance parameters and namely μ FE = 0.18 cm 2 /Vs, I on/off = 10 4 and turn-on voltage b 5 V were obtained for the n-type OFET based on a naphthalene bisimide derivative. Another group of devices developed is comprised of transistors based on active material single crystals. In this case, dithiophene-tetrathiafulvalene (DT-TTF) was used as a semiconductor, with the effect of its crystalline form on the transistor performance being investigated. Of the two DT-TTF polymorphs, monoclinic α form and hexagonal β form, the OFETs based on the α form were characterized by field-effect charge carrier mobility nearly an order of magnitude higher. In general, the results presented in the paper show both a broad applicability of parylene films in the technology of organic field-effect transistors and a versatile role these films may play in that technology.
    Full-text · Article · Sep 2015 · Surface and Coatings Technology
  • Source
    • "Rubrene is an ideal compound to study the interactions between oxygen and single crystal OSCs for three reasons. First, as single crystal rubrene displays the “best” electronic and optoelectronic properties of any OSC, with charge carrier mobility reaching up to 20 cm2V−1s−1 in reproducible experiments, it has been the subject of numerous studies89101112131415161718. Secondly, the existing understanding of the mechanism of reactions between oxygen and free rubrene molecules in gas or solution phases19202122, may facilitate the understanding of the interaction of oxygen with a solid-state form of this material, namely single crystalline rubrene. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Single crystal rubrene is a model organic electronic material showing high carrier mobility and long exciton lifetime. These properties are detrimentally affected when rubrene is exposed to intense light under ambient conditions for prolonged periods of time, possibly due to oxygen up-take. Using photoelectron, scanning probe and ion-based methods, combined with an isotopic oxygen exposure, we present direct evidence of the light-induced reaction of molecular oxygen with single crystal rubrene. Without a significant exposure to light, there is no reaction of oxygen with rubrene for periods of greater than a year; the crystal's surface (and bulk) morphology and chemical composition remain essentially oxygen-free. Grand canonical Monte Carlo computations show no sorbtion of gases into the bulk of rubrene crystal. A mechanism for photo-induced oxygen inclusion is proposed.
    Full-text · Article · May 2014 · Scientific Reports
  • Source
    • "The use of soluble organic semiconductors enables fabrication of plastic electronic devices, such as organic field effect transistors (OFETs), organic light emitting diodes and organic solar cells, with both low cost and low energy consumption123. In particular, organic single crystals have been reported to exhibit high performance in OFETs because of the absence of grain boundaries and the resulting low defect density45678910111213141516. However, to integrate organic single crystals into practical devices as active materials two techniques must be developed. "
    [Show abstract] [Hide abstract]
    ABSTRACT: A facile solution process for the fabrication of organic single crystal semiconductor devices which meets the demand for low-cost and large-area fabrication of high performance electronic devices is demonstrated. In this paper, we develop a bottom-up method which enables direct formation of organic semiconductor single crystals at selected locations with desired orientations. Here oriented growth of one-dimensional organic crystals is achieved by using self-assembly of organic molecules as the driving force to align these crystals in patterned regions. Based upon the self-organized organic single crystals, we fabricate organic field effect transistor arrays which exhibit an average field-effect mobility of 1.1 cm(2)V(-1)s(-1). This method can be carried out under ambient atmosphere at room temperature, thus particularly promising for production of future plastic electronics.
    Full-text · Article · May 2012 · Scientific Reports
Show more