Variable temperature mobility analysis of n-channel, p-channel and ambipolar organic field-effect transistors

Joseph A. Letizia, Jonathan Rivnay, Antonio Facchetti, Mark A. Ratner, Tobin J. Marks

Research output: Contribution to journalArticle

78 Citations (Scopus)

Abstract

The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5‴-bis(perfluorophenacyl)-2,2′:5′,2″:5″, 2‴-quaterthiophene (1, n-channel), 5,5‴-bis(perfluorohexyl carbonyl)-2,2′:5′,2″:5″,2‴-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5‴-bis(hexylcarbonyl)-2,2′: 5′,2″:5″,2‴-quaterthiophene (4, ambipolar), 5,5‴-bis-(phenacyl)-2,2′:5′,2″:5″, 2‴-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen- 2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N-(2-octyldodecyl)-2, 2′-bithiophene-3,3′-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (μeff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1-3 of 21, 22, and 30 meV, respectively. Higher EA values of 40-70 meV are exhibited by 4-7-derived FETs having lower mobilities (μeff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and μeff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits E A = 27 meV, the p-channel regime exhibits significantly more trapping with EA = 250 meV. Interestingly, calculated free carrier mobilities (μo) are in the range of ∼0.2-0.8 cm2 V -1 s-1 in this materials set, largely independent of μeff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (V T) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature μeff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature μeff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set.

Original languageEnglish
Pages (from-to)50-58
Number of pages9
JournalAdvanced Functional Materials
Volume20
Issue number1
DOIs
Publication statusPublished - Jan 8 2010

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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