A liquid crystalline copper phthalocyanine derivative for high performance organic thin film transistors

Abstract

Bottom-gate, bottom-contact organic thin film transistors (OTFTs) were fabricated using solvent soluble copper 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine as the active semiconductor layer. The compound was deposited as 70 nm thick spin-coated films onto gold source-drain electrodes supported on octadecyltrichlorosilane treated 250 nm thick SiO 2 gate insulators. The performance of the OTFTs was optimised by investigating the effects of vacuum annealing of the films at temperatures between 50C and 200 C, a range that included the thermotropic mesophase of the bulk material. These effects were monitored by ultraviolet-visible absorption spectroscopy, atomic force microscopy and XRD measurements. Device performance was shown to be dependent upon the annealing temperature due to structural changes of the film. Devices heat treated at 100 C under vacuum ($10 À7 mbar) were found to exhibit the highest field-effect mobility, 0.7 cm 2 V À1 s À1 , with an on-off current modulation ratio of $10 7 , a reduced threshold voltage of 2.0 V and a sub-threshold swing of 1.11 V per decade.

Solution-Processed Organic Field Effect Transistor Using a Liquid Crystalline Semiconductor, 8TNAT8

“…Numerous of the characteristic properties of liquid crystalline (LC) semiconductors, such as their selfassembling nature, electrically inactive domain boundaries, and good solubility in ordinary organic solvents, make them attractive candidates for application in FET devices [4][5][6][7][8][9][10][11][12][13][14][15][16]. Calamitic LC semiconductors have the advantage of achieving the 2D hopping conduction required for lateral type thin film transistors such as FETs, in contrast to the 1D hopping conduction shown by disc-shaped molecules.…”

Light absorption and hole-transport properties of copper corroles: from aggregates to a liquid crystal mesophase

“…1 In this regard, their ability to produce large assemblies or aggregates is particularly employed to construct organized and high light-absorbing materials displaying efficient charge and/or exciton transport properties that are essential in the preparation of organic solar cells 2 or photoconductors. 7 Corrole and its metal complexes are currently attractive members of the porphyrinoid family since their syntheses 8 and functionalizations 9 have been extensively developed during the last fifteen years and are thus amenable to gram-scale synthesis, sometimes essential for developing devices. 5 For example, an exciton diffusion length longer than 12 nm has been measured in a nematically organized porphyrin layer 6 while a field-effect mobility of 0.7 cm 2 V -1 s -1 was exhibited by an Organic Field Effect Transistor (OFET) incorporating a liquid crystalline copper phthalocyanine.…”

Hybrid phthalocyanine/lead sulphide nanocomposite for bistable memory switches

“…However, reported investigations of hybrid memory devices incorporating semiconductor quantum dots in a phthalocyanine matrix are relatively few, in part because of inherent difficulties with thermal evaporation. Phthalocyanine compounds with lipophilic substituents are soluble in common organic solvents and exhibit discotic liquid crystalline behaviour with the cores stacking along columns provide a route to employ these molecules in a cost-effective fabrication of organic electronic devices such as high performance organic thin film transistors as reported [28].…”