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.

Time of flight photocurrent transient studies on thin films of bimodal polytriarylamine (PTAA) show two distinct and separate arrival times for hole transport in the same sample at a single field. The corresponding mobilities differ by two orders of magnitude, typically μfast∼10−3 cm2 V−1 s−1 and μslow∼10−5 cm2 V−1 s−1 at room temperature, and are measured parametric in electric field and temperature. The mobility data are analyzed using the correlated disorder model by Novikov, yielding a fitting parameter set. The two conduction paths are believed to come about as a result of phase segregation between the shorter and longer polymer chains with the shorter chains giving rise to the faster conduction pathways (as confirmed by results obtained for monomodal, shorter, and longer chain PTAA, by sample thickness scaling of the photocurrents and by reversal of the illuminated electrode). Separate arrival times are also obtained in a blend of the two short and long chain monomodal polymers. The phase separation within the film is inferred by the appearance of two glass transition temperatures using dynamic mechanical thermal analysis.

The class of liquid-crystalline semiconducting polymers based on poly(2,5-bis(3-alkylthiophen-2yl)thieno[3,2-b]thiophene) recently has attracted significant interest in the field of organic electronics, predominantly due to their promising performance in field-effect transistor (FET) structures with device mobilities reaching-if not exceeding-those of amorphous silicon architectures. Less is known, however, about the bulk charge-transport properties of these interesting macromolecules. We therefore conducted time-of-flight (TOF) photoconductivity measurements on one particular material of this class of organic semiconductors-i.e. poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene), pBTTT-C 12 -and attempted to correlate the electronic bulk properties of this polymer with its microstructural development with temperature. The effect of annealing was also investigated.

Time of flight photocurrent transient studies on 5 μm thick solution processed films of novel non-peripherally octa-octyl-substituted liquid crystalline gadolinium bis-1,4,8,11,15,18,22,25octakis(octyl) phthalocyanines (8GdPc 2 ) 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 −6 m 2 V −1 s −1 and 1.6×10 −6 m 2 V −1 s −1 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.

Time-of-flight measurements on 2 μm thick drop-cast films of 1,4,8,11,15,18,22,25octakis(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 cm 2 V −1 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.

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 (5 μm) and long (20 μm) 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 = 5 μ m than those for L = 20 μm.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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 SiO2 gate insulator. The analysis of experimental results showed the n-type field effect behaviour. Devices annealed at 100 oC under vacuum were found to exhibit the field-effect mobility of 0.0989 cm2 V−1 s−1, with an on/off current modulation ratio of ∼106, a reduced threshold voltage of 0.7 V and a sub-threshold swing of 2.12 V decade−1. The variations in surface morphology of the devices are found reflected considerably in the electrical measurements. The device contact resistance was found to be decreased as the gate bias increased and also with the annealing.