The structural and transport properties of evaporated pentacene organic thin film transistors (TFTs) are reported, and they show the influence of the deposition conditions with different inorganic dielectrics. Dielectrics compatible with large area fabrication were explored to facilitate low cost electronics on glass or flexible plastic substrates. X-ray diffraction and atomic force microscopy show a clear correlation between the morphology and the structure of the highly polycrystalline films for all dielectrics investigated. The roughness of the dielectric has a distinct influence on the morphology and the structural properties, whereas the films on smooth thermal oxide are in general highly ordered and independent of the deposition conditions. The ordered films exhibit a “thin film” and a bulk phase, and the bulk phase volume fraction increases with the deposition temperature and the film thickness. Careful control of the deposition conditions gives virtually identical films on thermal oxide and silicon nitride dielectrics. The electronic properties of inverted staggered transistors show that the TFT mobility is correlated with the morphology and structure of the films. The TFTs exhibit very similar mobilities of ∼0.4 cm2/Vs and on/off ratios >108 on thermal oxide and silicon nitride. The impact of the dielectric on the device parameters of mobility, threshold voltage, and subthreshold voltage slope is discussed. Temperature dependent measurements of the mobility were performed to study the influence of traps on electronic transport. Bias stress experiments were carried out to investigate the stability of the TFTs, and to gain understanding of the transport mechanisms of thermally evaporated pentacene TFTs.

The transport properties of high-performance thin-film transistors (TFT) made with a regio-regular poly(thiophene) semiconductor (PQT-12) are reported. The roomtemperature field-effect mobility of the devices varied between 0.004 cm 2 /V s and 0.1 cm 2 /V s and was controlled through thermal processing of the material, which modified the structural order. The transport properties of TFTs were studied as a function of temperature. The field-effect mobility is thermally activated in all films at T<200 K and the activation energy depends on the charge density in the channel. The experimental data is compared to theoretical models for transport, and we argue that a model based on the existence of a mobility edge and an exponential distribution of traps provides the best interpretation of the data. The differences in room-temperature mobility are attributed to different widths of the shallow localized state distribution at the edge of the valence band due to structural disorder in the film. The free carrier mobility of the mobile states in the ordered regions of the film is the same in all structural modifications and is estimated to be between 1 and 4 cm 2 /V s.2 1-IntroductionThe carrier mobility of polymer semiconductors has improved tremendously over the past few years. Field-effect mobility as high as 0.1 cm 2 /V s has recently been measured in regio-regular poly(thiophenes). [1][2][3] Transport characteristics are strongly dependent on the degree of order of the polymer semiconductor at the dielectric interface. Because the structure of the polymer depends on the processing conditions, it is not uncommon to find in the literature widely differing mobility values obtained for nominally the same polymer. In particular, the energy of the dielectric surface prior to the deposition of the polymer, 4-7 the solvent evaporation rate, 2 the molecular weight of the polymer 8 and thermal post-processing of the film 9 all influence the carrier mobility.There is no general consensus on the mechanism of charge transport in these amorphous or poly-crystalline materials. A complete model of the electrical properties should include a description of the energy distribution of the carriers and how the conduction varies as a function of energy. Disorder-induced localized states are clearly important for the transport, and the essential question is the relation between atomic structure, electronic structure and the transport. Generally, charge transport in disordered materials is described either as hopping between localized states, or trapping and release from localized states into a higher energy mobile state. 10 The degree of structural order may change the mechanism even within the same class of polymer.Because the electronic structure of semiconducting polymer films is not known experimentally, a simplified model has to be assumed. The model proposed by Bässler 11 assumes that the energy distribution of the carriers is Gaussian due to the random disorder in the material. The standard deviation of the Gaussian (typicall...

Temperature-dependent measurements of thin-film transistors were performed to gain insight in the electronic transport of polycrystalline pentacene. Devices were fabricated with plasma-enhanced chemical vapor deposited silicon nitride gate dielectrics. The influence of the dielectric roughness and the deposition temperature of the thermally evaporated pentacene films were studied. Although films on rougher gate dielectrics and films prepared at low deposition temperatures exhibit similar grain size, the electronic properties are different. Increasing the dielectric roughness reduces the free carrier mobility, while low substrate temperature leads to more and deeper hole traps.

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We present a zinc|ferricyanide hybrid flow battery that achieves extensive first-pass desalination while simultaneously supplying electrical energy (10 Wh/L). We demonstrate 85% salt removal from simulated seawater (35 g/L NaCl) and 86% from hypersaline brine (100 g/L NaCl), together with reversible battery operation over 100 h with high round-trip efficiency (84.8%). The system has a high operating voltage (E 0 = +1.25 V), low specific energy consumption (2.11 Wh/L for 85% salt removal), and a desalination flux (4.7 mol/m 2 •h) on par with that of reverse osmosis membranes. Salt removal was similarly effective at higher feed salinities, for which reverse osmosis becomes physically impossible because of the pressure required. The results have positive implications for regions that rely on desalination for their freshwater needs, especially where sea salinity is high. Alternatively, the battery may also be useful in minimal liquid discharge wastewater treatment if operated as a brine concentrator.