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ABSTRACT: We present a study performed on organic thin film transistors based on poly(3-hexylthiophene) with molecular weights ranging from 20 to 80 kDa as active material. Besides having a strong influence on the absolute value of the mobility, we show that the molecular weight also drastically affects the mobility functional dependence on the gate voltage and on the longitudinal electric field. While the medium range of molecular weight (37–53 kDa) yields a high (about 10<sup>-2</sup> cm <sup>2</sup>/ V s ) and practically constant mobility, the low and high ranges yield a lower mobility, which in addition shows a strong dependence on both the charge density and the electric field. By means of a detailed analysis of experimental transfer characteristics of transistors, this behavior is traced back to the broadness of the density of states, which turns out to be higher for low mobility polymers. Finally, consequences on transistor modeling due to the simultaneous dependence of the mobility on charge density and electric field are discussed.
Journal of Applied Physics 11/2008; · 2.17 Impact Factor
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JOURNAL OF APPLIED PHYSICS. 01/2007; 101:-.
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W. Porzio,
S. Destri,
M. Pasini,
A. Bolognesi,
A. Angiulli,
P. Di Gianvincenzo,
D. Natali,
M. Sampietro,
M. Caironi, L. Fumagalli,
S. Ferrari,
E. Peron,
F. Perissinotti
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ABSTRACT: Derivatives of both oligo- and polythiophene-based FET were recently considered for low cost electronic applications. In the device optimization, factors like redox reversibility of the molecule/polymer, electronic level compatibility with source/drain electrodes, packing closeness, and orientation versus the electrodes, can determine the overall performance. In addition, a gate insulator with a high dielectric constant, a low leakage current, and capability to promote ordering in the semiconductor is required to increase device performances and to lower the FET operating voltage. In this view, Al2O3 appears a good candidate, although its widespread adoption is limited by the disorder that such oxide induces on the semiconductor with detrimental consequences on semiconductor electrical properties.In this contribution, an overview of recent results obtained on thiophene-derivative-based FET devices, fabricated by different growth techniques, and using both thermally grown SiO2 and Al2O3 from atomic layer deposition gate insulators will be reported and discussed with particular reference to organic solid state aggregation, morphology, and organic–inorganic interface.
Materials Science and Engineering: C. 26:996-1001.
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ABSTRACT: We studied organic thin film transistors based on poly-(3-hexylthiophene) having as gate dielectric Al2O3, which was prepared by atomic layer deposition (ALD) technique, that provides films with very good electrical properties, roughness below 1 nm and compatibility with virtually any type of substrate, including polymeric ones. High-k gate oxides such as Al2O3 are advantageous since they enable a reduction of operating voltages, but when used in conjunction with organic semiconductors, they induce worse transport properties if compared to low-k dielectrics. To address this issue, we focused on the interface between the gate dielectric and the active material and we explored the effects of functionalizing the Al2O3 surface by means of self-assembled monolayers (SAM). We studied and compared a set of SAMs differing in the ligand groups and in the chain lengths. We show that the most important parameter is the SAM chain length, the longer SAM being more effective in giving better charge carrier mobility. The microscopical origins of this finding are analyzed exploiting and comparing the dependence of the mobility on the gate voltage in the transistors based on the variously functionalized Al2O3. With n-octadecyltrichlorosilane (OTS) the mobility reaches the value of 10−2 cm2/V s, comparable to the mobility on transistors with properly functionalized SiO2 gate dielectric.
Organic Electronics 9(2):198-208. · 4.05 Impact Factor
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ABSTRACT: The strong sensitivity of organic/polymeric semiconductors to the exposure to O2 and H2O atmospheres makes the use of capping layers mandatory for the realization of stable devices based on such materials. In this paper we explore the realization of inorganic capping layers by atomic layer deposition (ALD) that provides smooth and pinhole-free films with a great potential as passivation layer for organic based devices. We show that the deposition of Al2O3 on transistors based on poly-3 hexyltiophene (P3HT) allows to obtain air stable devices. Whereas the growth of Al2O3 directly on the P3HT layer leads to a rough interface and significant intermixing between the oxide and the polymer, which results in a deterioration of transistor performances, an interlayer of a poly-alcohol such as poly-vinylphenol interposed between the Al2O3 and the P3HT gives a well defined Al2O3/polymer interface without degradation of the hole mobility. Transistors capped with Al2O3/PVP are very stable in air, with no appreciable differences in the electrical characteristics when measured in vacuum or in air. In addition no significant degradation of the transistors electrical properties was detected even after one month of air exposure.
Organic Electronics.
