Influence of molecular weight on the short-channel effect in polymer-based field-effect transistors

Ali Veysel Tunc, Bernhard Ecker, Zekeriya Dogruyol, Sabrina Juechter, Ahmet Lutfi Ugur, Ali Erdogmus, Sait Eren San, Juergen Parisi, Elizabeth von Hauff

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Abstract

In this study, we demonstrate how the intrinsic properties of a polymer can influence the electrical characteristics of organic field-effect transistors (OFETs). OFETs fabricated with three batches of poly[2-methoxy,5-(3′,7′-dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) were investigated. The properties of the polymers were initially investigated using Fourier transform infrared spectroscopy (FTIR), impedance spectroscopy (IS), gel permeation chromotography (GPC), and cyclic voltammetry (CV), respectively. The structure and purity of the polymer batches were found to be very comparable, but the molecular weight (Mn and Mw) and polydispersity (PDI = Mw/Mn), varied between the samples and the HOMO and LUMO levels of the polymers were found to depend on the molecular weight properties. OFETs were then fabricated with the polymers and electrically characterized. It was observed that the channel current and the field-effect mobility increase with increasing polymer molecular weight. The output characteristics of the transistors, on the other hand, were found to depend on the PDI of the polymer. Saturation of the channel current occurs at higher source–drain voltages and short-channel behavior was observed to start at longer channel lengths for polymers with a higher PDI. This behavior is observed to be thickness dependent, and the short-channel behavior was more pronounced for thicker MDMO-PPV films. These results are explained in terms of influences of chain packing and ordering and high bulk currents on the FET output and transistor parameters. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 117–124, 2012
Original languageEnglish
Pages (from-to)117-124
JournalJOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS
Volume50
Issue number2
DOIs
Publication statusPublished - 15 Jan 2012

Keywords

  • charge transport
  • conjugated polymers
  • disorder
  • molecular weight distribution
  • structure-property relations

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