Channel Length Dependent Characterisations of Organic Thin Film Transistors with Solution Processable Gadolinium Phthalocyanine Derivatives

Spin-coated 52-nm-thick films of newly synthesised gadolinium liquid crystalline bisphthalocyanine sandwich (GdPc 2) complexes with octyl chains non-peripheral positions have been successfully employed as active layers for bottom-gate organic field effect transistors having both short (5μm) and long (20μm) channels. The scaling down of the channel length (L) decreases the field effect mobility due to the increase in the contact resistance between the gold electrodes and the GdPc 2 semiconducting layer. Values of on–off ratio and sub-threshold voltage swing are higher nearly one order of magnitude for L=5μm than those for L=20μm

Newly Synthesised Gadolinium bis-Phthalocyanine Sandwich Complex: Ambipolar Organic Semiconductor

Time of flight (TOF) photocurrent transient studies on 5µm thick solution processed films of novel non-peripherally octa-octyl-substituted liquid crystalline gadolinium bis-1,4,8,11,15,18,22,25-octakis(octyl) phthalocyanines (8GdPc2) provide a quantitative analysis of the intrinsic ambipolar charge transport relative to mesomorphic structure of this lanthanide compound. Characteristic liquid crystalline phases of these molecules have been identified from differential scanning calorimetry supported by observation from the UV-visible absorption, showing crystal-columnar mesophase and columnar mesophase-isotropic liquid transitions at 64.2°C and 162°C, respectively. The TOF carrier mobility is found to be structure dependent and highest values of 4.73×10−6m2/Vs and 1.6×10−6m2/Vs have been estimated for hole and electron mobilities for hexagonally packed, columnar structures of the spin-coated films. These results are exploitable for development of single molecule based all organic complimentary analogue and digital circuits with tunable field effect performance

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

This journal is © The Royal Society of Chemistry 2012Bottom-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 SiO2 gate insulators. The performance of the OTFTs was optimised by investigating the effects of vacuum annealing of the films at temperatures between 50 0C and 200 0C, 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 0C under vacuum (≥10-7 mbar) were found to exhibit the highest field-effect mobility, 0.7 cm2 V^-1 s^-1, with an on–off current modulation ratio of~107, a reduced threshold voltage of 2.0 V and a sub-threshold swing of 1.11 V per decade.UK Technology Strategy Board (Project no: TP/6/EPH/6/S/K2536J) and UK National Measurement System (Project IRD C02 ‘‘Plastic Electronics’’, 2008–2011)

Ambipolar charge transport in non-peripherally substituted octahexyl zinc phthalocyanine

Time-of-flight measurements on $2\ \mu\text{m}$ thick drop-cast films of 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyaninato zinc complex in a sandwich configuration between transparent indium tin oxide and aluminum metal electrodes have been performed. The results show that intrinsic ambipolar transport characteristics are exhibited by this very stable compound having values in the order of $10^{-4}\ \text{cm}^{2}\,\text{V}^{-1}\,\text{s}^{-1}$ for both types of charge carrier. Both electron and hole transport are dispersive due to a high degree of positional disorder of the molecules