Polymorphism and Charge Transport in Vacuum-Evaporated Sexithiophene Films

Servet, Bernard; Horowitz, Gilles; Ries, Stefan; Lagorsse, O.; Alnot, P.; Yassar, Abderrahim; Deloffre, Françoise; Srivastava, Pankaj; Hajlaoui, Riadh

doi:10.1021/cm00046a039

Cited by 279 publications

(215 citation statements)

References 0 publications

Supporting

Mentioning

194

Contrasting

Order By: Relevance

“…Such an arrangement is preserved over thicknesses of up to several micrometers, and makes the film a two-dimensional medium, in which the charge transport is favored in the direction parallel to the film, and hence perpendicular to the long axis of the molecules. Such an interpretation was confirmed when highly ordered films of the unsubstituted 6T were grown by heating the substrate and using low deposition rates, [31] which resulted in both a molecular packing and a field-effect mobility similar to that of DH6T. Identical results have been reported more recently by the Bell Labs group for both 6T [32] and DH6T.…”

Section: Oligothiophenessupporting

confidence: 63%

Organic Field-Effect Transistors

Horowitz¹

1998

Adv. Mater.

2,351

1,585

View full text Add to dashboard Cite

Organic field-effect transistors (OFETs) were first described in 1987. Their characteristics have undergone spectacular improvements during the last two or three years. At the same time, several models have been developed to rationalize their operating mode. In this review, we examine the performance of OFETs as revealed by recently published data, mainly in terms of field-effect mobility and on±off current ratio. We compare the various compounds that have been used as the active component, and describe the most prominent fabrication techniques. Finally, we analyze the charge transport mechanisms in organic solids, and the resulting models of OFETs.

show abstract

Section: Oligothiophenessupporting

confidence: 63%

Organic Field-Effect Transistors

Horowitz¹

1998

Adv. Mater.

2,351

1,585

View full text Add to dashboard Cite

show abstract

“…Interestingly, the diffraction data for thin films of 1, 2, and 3 indicated larger layer spacings than measured for their bulk counterparts, suggesting the existence of a ªthin-filmº phase, not unlike behavior observed for sexithiophene and pentacene thin films. [14,15] Notably the difference between the thin-film and bulk diffraction data for 1 and 3 is much larger than for 2, which exhibits only slight shifts in 2h corresponding to a 1 decrease in the layer d-spacing. This may reflect odd±even effects, with respect to the number of thiophene rings, on molecular packing.…”

Section: Resultsmentioning

confidence: 99%

Organic Thin‐Film Transistors Based on Tolyl‐Substituted Oligothiophenes

Mohapatra

Holmes

Newman

et al. 2004

Adv Funct Materials

View full text Add to dashboard Cite

Thin films based on the tolyl‐substituted oligothiophenes 5,5′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′‐terthiophene (1), 5,5′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene (2) and 5,5′′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′‐quinqethiophene (3) exhibit hole‐transport behavior in a thin‐film transistor (TFT) configuration, with reasonable mobilities and high current on/off (Ion/Ioff) ratios. Powder X‐ray diffraction (PXRD) reveals that these films, grown by vacuum deposition onto the thermally grown silicon oxide surface of a TFT, are highly crystalline, a characteristic that can be attributed to the general tendency of phenyl groups to promote crystallinity. Atomic force microscopy (AFM) reveals that the films grow layer by layer to form large domains, with some basal domain areas approaching 1000 μm2. The PXRD and AFM data are consistent with an “end‐on” orientation of the molecules on the oxide substrate. Variable‐temperature current–voltage (I–V) measurements identified the activation regime for hole transport and revealed shallow level traps in thin films of 1 and 2, and both shallow and deep level traps in thin films of 3. The activation energies for thin films of 1, 2, and 3 were similar, with values of Ea = 121, 100, and 109 meV, respectively. The corresponding trap densities were Ntrap/Nv = 0.012, 0.023, and 0.094, where Ntrap is the number of trap states and Nv is the number of conduction states. The hole mobilities for the three compounds were similar (μ ≃ 0.03 cm2 V–1 s–1), and the Ion/Ioff ratios were comparable with the highest values reported for organic TFTs, with films of 2 approaching Ion/Ioff = 109 at room temperature.

show abstract

“…In some cases, this enables the preparation of well-ordered polycrystalline films. This is often an advantage in the operation of the device concerned, for example, for transport of electric charge in field-effect transistors, resulting in relatively high electrical mobilities for FET applications [26], potentially faster switching speeds for electro-optical devices and enhanced chargecarrier separation and lower internal resistance [27] in photo-voltaic applications.…”

Section: Sublimationmentioning

confidence: 99%