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Made available in DSpace on 2022-04-29T08:46:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Few works on solution-processed zinc oxide vertical transistors and electrolyte-gated transistors have shown the merits of both architectures. Here, we present an electrolyte-gated vertical field-effect transistor (EGVFET) based on a spray-deposited zinc oxide/silver nanowire (ZnO/AgNW) Schottky contact. The output curve shows that the device operates at a sub-1 V bias. Also, the electrolyte does not affect the diode cell, and the cyclic voltammetry of the capacitor cell does not indicate a faradic process between AgNW and the top-gate electrode. From the transfer curve, we extracted an ION/IOFF ratio of 104, an on-current density of 65.3 mA/cm2 and a normalized transconductance of 113.4 S/cm2. Our contribution places the ZnO-EGVFET structure on the front line to develop printed transistors without a high-resolution pattern. São Paulo State University – UNESP, Faculty of Science and Technology (FCT), Physics Department, Presidente Prudente, SP, Brazil. (e-mail: leonardo.nogueira@unesp.br) São Paulo State University – UNESP, Faculty of Science and Technology (FCT), Physics Department, Presidente Prudente, SP, Brazil. Universidade Federal do Paraná – UFPR, Physics Department, Curitiba, PR, Brazil. Universidade Tecnológica Federal Do Paraná – UTFPR, Physics Department, Curitiba, PR, Brazil.

The improvement of electron transport in polymer semiconductors is highly desirable for realizing robust, large-area and low-cost organic integrated circuits. This work investigates the effect of regioregularity on the intrinsic hole and electron transport characteristics of poly(3-hexylthiophene-2,5-diyl) (P3HT) using current-voltage (I-V) measurements in metal/polymer/metal sandwich structures. Through a direct comparison between 93% regioregular P3HT (EG-P3HT) and 100% regioregular defect-free poly(3-hexylthiophene-2,5-diyl) (DF-P3HT), it is found that the elimination of regioregularity defects improves the electron mobility of DF-P3HT (1.05 × 10-7 cm2 V-1 s-1) by three orders of magnitude compared to the 93% regioregular EG-P3HT sample (1.82 × 10-10 cm2 V-1 s-1). Quantum chemical calculations indicate that the improvement of electron mobility in DF-P3HT can be associated to the lower degree of disorder in these samples that tends to increase the transfer angle between the lowest unoccupied molecular orbitals of adjacent chains. At the same time, the lower dipole moments produced by the defect-free polymer molecules also appears to play an important role in decreasing the susceptibility of charge transport to environment-induced electron traps. The obtained results provide a strong evidence that the elimination of regioregularity defects is an effective technique to improve electron transport and restore the symmetry between hole and electron mobility in P3HT as well as other thiophene-based polymers.

The thermal, electrical and morphological characterization of poly(3-hexylthiophene-2,5diyl) (P3HT) is presented and discussed. Thermal analyses revealed high glass transition, melting and degradation temperatures, indicating high stability of the polymer to annealings in the range 25–200°C. Electrical measurements were performed in spin-coated devices constructed using indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) in the sandwich structure ITO/PEDOT:PSS/P3HT/Al. The devices were thermally treated at 25°C, 100°C, 150°C, and 200°C prior to the measurements. Characteristic curves of current density versus voltage showed that the injection of charge carriers is governed by tunneling at high electric fields. Hole mobility was estimated by impedance spectroscopy, showing a maximum value of 8.6 × 10−5 cm2/Vs for annealed films at 150°C. A thermally stimulated current technique was used to analyze the trap density in the P3HT and its respective energies for all devices, presenting the lowest trap density for annealed films at 150°C. Morphological features observed by atomic force microscopy showed that the 150°C thermally treated film presents the best interface condition of the four investigated annealing temperatures.

The chemical vapour sensing behaviour of pristine and variously modified hexagonal boron nitride (hBN) nanostructures was investigated towards the polar protic analyte in the form of ammonia. Morphological characterization with TEM revealed formation of well-define shaped and crystal sized hBN flakes (2.9 ± 0. 7 µm to 3.3 ± 0.3 µm) by using a low temperature and atmospheric pressure modified polymer derived ceramics (PDCs) route. Room temperature chemical sensing studies showed that the hBN-based devices were sensitive to ammonia, at sensitivity values of 2.8 × 10−2 ppm−1 for the pristine hBN flakes, and 2.0 × 10−2 ppm−1, 2.4 × 10−2 ppm−1, 2.1 × 10−2 ppm−1 for the 2.5, 5 and 10 wt.% BaF2 modified hBN flakes, respectively. On the contrary, improvement in structure for the 5 wt.% BaF2 modified hBN flakes had detrimental influence on the detection performance of ammonia, as evidenced by the poor LoD value of 49.7 ppm, in comparison to 1.1, 2.4 and 1.7 ppm for the pristine, 2.5, and 10 wt.% BaF2 modified hBN flakes, respectively. The improved sensing performance was attributed to the presence of nitrogen vacancies generated during the modification process, as well as the presence of impurities. Indeed, the values measured were higher than those reported for other 2D nanomaterial based sensors. This study demonstrates the critical role played by structural properties on the surface chemistry in the ammonia sensing properties of hBN flakes. Generally, the study highlighted the potential application of hBN nanostructured materials for detection of ammonia vapours at room temperature.

The high capacitance from an electrolyte dielectric layer used in a thin film transistor architecture results in the development of electrolyte-gated organic field effect transistors (EGOFETs), which are able to operate at lower voltages compared with the commonly organic field effect transistors. When ions diffuse into the semiconductor, changing its conductive properties, the resulting devices are named organic electrochemical transistors (OECTs). In this case, an increase in channel conductivity occurs due to ionic doping. Depending on the gate voltage range operation, it is possible to obtain a de-doping process, suitable for achieving a low off-current. In this work, a simple and easy method is proposed based on an additional dielectric layer deposition of poly(methyl methacrylate) at the electrolyte dielectric/semiconductor interface, which provides: (i) good efficiency to block the diffusion of anions into the channel, resulting in an EGOFET for a gate voltage range up to − 0.6 V and (ii) an improvement in the on–off ratio in approximately three orders of magnitude for OECTs due to the low off-current obtained without promoting ionic de-doping in the channel, for a gate voltage range up to − 1.1 V. Both modes of operation were obtained in the same transistor structure. In addition, parameters such as field effect mobility, on–off ratio, and threshold voltage were also estimated for different transistor structures and gate voltage ranges.

The structural properties of amorphous GaSe9 thin films produced by vacuum evaporation were investigated using the EXAFS technique and the cumulant expansion method. Structural parameters such as average coordination numbers and interatomic distances, disorder and asymmetry of the partial pair distribution functions gij(r) were obtained and compared to those found in the amorphous GaSe9 alloy used as precursor in the evaporation technique. Results indicate that structural units present in GaSe9 evaporate without dissociation, showing the stability of this alloy.

Made available in DSpace on 2018-11-26T16:40:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-07-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) LNLS The eletronic and optical properties of amorphous GaSe thin films produced by vacuum evaporation were investigated using X-ray photoemission spectroscopy (XPS) and transmittance spectroscopy techniques. XPS measurements allowed the determination of the valence band energy and showed the chemical bonding and the charge transfer between Se and Ga atoms. Transmittance measurements allowed the determination of the optical gap, refractive index and extinction coefficient in the low and high absorption regions. Using the Wemple and DiDomenico single oscillator model we also found the oscillator and the dispersive energies. From the valence band and optical gap energies, the conduction band was found and an energy level diagram for f-GaSe is proposed. Fac Tecnol SENAI CIC, CIC, R Senador Accioly Filho 298, BR-81310000 Curitiba, PR, Brazil Univ Fed Parana, Dept Fis, Ctr Polit, BR-81531990 Curitiba, PR, Brazil UNIOESTE, Ctr Engn & Ciencias Exatas, BR-85903000 Toledo, PR, Brazil Univ Estadual Paulista, Dept Fis, BR-17033360 Bauru, SP, Brazil Univ Estadual Paulista, Dept Fis, BR-17033360 Bauru, SP, Brazil LNLS: SXS-10976

Amphiphilic ruthenium bipyridine complexes based on 1,3,4-oxadiazole-pyridine ligands (L1, L2) were synthesized and characterized by 1H NMR, UV–Vis spectroscopy, electrochemistry and UV–Vis spectroelectrochemistry. The free ligands and the respective ruthenium(II) complexes exhibit an intraligand π−π∗ absorption band in the UV region that overlaps with the MLCT bands. The [Ru(bpy)2(L2)](PF6)2 complex with a bidentated L2 ligand did not form a stable monolayer in water-air interface demonstrating the relevance of coordination geometry on the molecular packing properties. In contrast, stable Langmuir-Blodgett films of the [Ru(bpy)2(L1)Cl]PF6 complex (RuL1) exhibiting reversible and fast spectroelectrochemical properties associated with the Ru(III/II) redox couple were obtained, where redox site inactivation become relevant above 20 monolayers where the current leveled up. Thin LB films were deposited on poly(bithiophene) to enhance its photoelectrochemical properties and realize photoresponsive AND and OR logic gate devices.

Magnetoresistance phenomenon on organic semiconductors has been studied mostly on spin-coated or vacuum thermal sublimated materials. In this work, electrochemistry is used as organic deposition technique. We report electrical measurements with an applied magnetic field on devices constructed in the sandwich structure indium tin oxide (ITO)/poly(bithiophene) (PBT)/aluminum (Al). The PBT polymer was electrochemically deposited on ITO. Hole mobility of 2.6 × 10−5 cm2/Vs was measured by impedance spectroscopy measurements, and thermally stimulated current measurements indicated two trapping states with activation energies around E 1–3 = 0.49 eV and E 4 = 0.51 eV. The interface ITO/PBT was characterized as a tunneling junction with ~0.9 eV energy barrier for hole injection from ITO. The highest magnetoresistance, ~0.6 %, was observed for a 273-nm PBT thickness, independent on direction between current and magnetic field.

We report on the development and characterization of an all-organic vertical transistor, consisting of a p-type conjugated polymer, poly(bithiophene), as collector material, a poly(ethylene dioxythiophene)/poly(styrene sulfonate) layer as base material and a n-type molecule layer, Alq3, as emitter material. The transistor is operated under direct bias in the common-emitter mode, being its operation based upon charge recombination of the injected majority carriers at the emitter–base interface. Experimental results have yielded current amplification factors up to 7. We also demonstrate that tunneling controls the transport characteristics of the device.

In this work we present a permeable base transistor consisting of a 60 nm thick N,N'diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine layer or a 40 nm thick 2,6-diphenyl-indenofluorene layer as the emitter, a CalAl/Ca multilayer as the metal base, and p-Si as collector. In the base, the Ca layers are 5 nm thick and the Al layer was varied between 10 and 40 nm. the best results obtained with a 20 nm thick layer. The devices present common-base current gain with both organic layer and silicon acting as emitter, but there is only observable common-emitter current gain when the organic semiconductor acts as emitter. The obtained common-emitter current gain, similar to 2, is independent on collector-emitter voltage, base current and organic emitter in a reasonable wide interval. Air exposure or annealing of the base is necessary to achieve these characteristics, indicating that an oxide layer is beneficial to proper device operation.

The molecular semiconductors are widely used on a great diversity of electronic and optoelectronic devices. The incorporation of molecular semiconductors to semiconductor- metal-semiconductor transistors (SMS) simplified the required production technology and, more importantly, allowed the construction of devices in vertical architecture with nearly ideal common-base current gains. In this work we present the results of the construction of SMS transistors utilizing an organic semiconductor, an indenofluorene derivative (DPIF), as emitter. The base and collector are respectively tin (Sn) and p- doped silicon (Si-p). The devices were electrically characterized at three-terminal measurements and were operated in common-base and common-emitter modes, revealing a permeable- base characteristic. The base thickness was varied in order to investigate the influence on the device performance. High current gain (~1) was obtained in common-base mode, and in common-emitter mode a current gain of 120 was achieved for a base thickness of 23 nm.

A new organic semiconductor, 2,6-diphenylindenofluorene (DPIF), was synthesized in four steps with a high overall yield of 49.3%. The morphology of thin films of DPIF that were formed under different substrate temperatures was examined by atomic force microscopy and X-ray diffraction analysis. Two different crystalline phases were found to exist depending on the deposition conditions. The DPIF thin film emits around 500–530 nm, while the OLED based on DPIF emits green light with a maximum output over 150 Cd/m2 under 35 V. Two typical transistor devices, thin-film transistor (TFT) and semiconductor-metal-semiconductor (SMS) transistor, were fabricated and characterized. DPIF shows a weak n-type character from the TFT device measurement, while SMS transistors using DPIF as an emitter behave like permeable-base transistors with low operating voltages in both common-base and common-emitter modes and a feature of current amplification. Our results demonstrate however, that further research efforts are necessary in order to prevent the observed instabilities. These are quite important, considering that the common-emitter mode is widely used in applications requiring not only switching capability, but also current amplification.

The synthesis of a conjugated copolymer, poly[(i,i'-ferrocenylenevinylene)-co-(2,5-di-n-octyloxy)-p-phenylenevinylene] (PFV-DOPPV) via McMurry coupling of i,i'-ferrocenedialdehyde and 2,5-di-n-octyloxybenzene-i,4-dialdehyde is reported. PFV-DOPPV was fully characterized by 1 H NMR, FTIR, FT-Raman, UV-VIS, cyclic voltammetry, size exclusion chromatography (SEC), inductively coupled plasma - optical emission spectrometry (ICP-OES), thermogravimetry (TG) and differential scanning calorimetry (DSC). The ionization potential, band-gap energy, electron affinity, HOMO and LUMO levels could be estimated. Electrical measurements in a sandwich device exposed to magnetic fields revealed magnetoresistance.

In this work we report efficiency measurements on light-emitting diodes with electrochemically synthesized sulfonated polyaniline as hole transport layer. The anode used in our devices is fluorine-doped tin oxide, the blocking layer is electrochemically synthesized poly(9,9-dioctyl-1,4-fluorenylenevinylene) and the electron transporting material and emitter is tris-(8-hydroxyquinoline) aluminum. Sulfonated polyaniline based devices presented efficiency of 0.79 cd/A.

We report the electrochemical preparation of poly(p-phenylene) (PPP) thin films with a polymerization degree of approximately 20 using biphenyl as starting material. The PPP films are prepared directly on a tin oxide electrode, presenting a positive charge carrier mobility of 5×10−7 cm2 V−1 s−1.

We report on gallium–selenium alloy (GaSe9) thin films simultaneously functioning as both blocking layer and active layer on poly(3-hexylthiophene-2, 5-diyl) (P3HT)-based organic photodiodes in order to enhance device performance. In addition to improved transport of the photogenerated charge carriers, GaSe9 films also contribute to light absorption on a different wavelength interval than that of P3HT. Three different devices are compared: ITO/GaSe9/Al, ITO/P3HT/Al and ITO/P3HT/GaSe9/Al, with the last one presenting a lower dark current density (0.90 μA cm−2), higher ON/OFF current ratio (61) and fastest response under AM 1.5 light irradiance. The observed responsivity is 7.3 mA W−1 and is almost linearly dependent on irradiance in the range 0.6–60 W m−2. A maximum external quantum efficiency of 135% and specific detectivity of 16.7 × 1011 Jones at 390 nm incident light wavelength are obtained.

We report on vertical architecture hybrid transistor devices using p-type silicon as collector terminal and 2,6-diphenylindenofluorene as organic semiconductor in the emitter layer. Polystyrene spheres were used as shadow masks in order to control the diameter and density of the openings in the Al metallic base. Two processes of sphere deposition were used: electrospray and dip-coating. The electrospray deposition leads to a smaller density of sphere agglomerates, but for the used sphere diameter, approximately 200 nm, the transistor performance is similar for devices prepared with sphere deposition by both techniques. The so constructed permeable-base transistors show common-emitter current gain of the order of 10(2).

Selenium : phosphour (SeP) thin films produced by thermal sublimation in vacuum are used as hole injection layers (HILs) in tris(8-hydroxyquinolinato) aluminum (Alq3) based devices. These devices are constructed in the sandwich structure substrate/HIL/Alq3/Al using three different substrate electrodes: fluorine doped tin oxide, Au, and indium tin oxide. The obtained electrical measurements indicate a better injection of positive charge carriers using the SeP layer. Syncrotron radiation x-ray photoelectron experiments allowed the determination of the work function of SeP. The obtained value (Φ = 5.6 eV) is close to the HOMO energy level of Alq3 and is consistent with the better positive charge injection. The thermionic injection process is suggested to be responsible for the charge injection from the different substrate electrodes into the SeP material. From transmittance measurements it was possible to calculate the refractive index and absorption coefficient as a function of wavelength, and to estimate the optical band gap (Eg = 1.9 eV). The latter and the measured work function were used in the construction of an energy level diagram of the SeP thin films used as HILs in organic devices. The hole injection efficiency of the produced films are compared with results using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT : PSS).

Bipolar devices constructed using 60nm thick tris-(8-hydroxyquinoline) aluminum (Alq3) thin films sandwiched between a 200nm thick sulfonated polyaniline hole-injection electrode and Al∕Ca electron-injection electrode show very high (up to 103%) magnetocurrent values. True-hole-only and true-electron-only Alq3-based devices that make use of Si as charge carrier collecting electrode, and Al∕Ca as electron injecting electrode or Au as hole injecting electrode, are also proposed, prepared, and characterized. In these true-single-carrier devices magnetocurrent is not observed. This result provides strong evidence that bipolar injection is a necessary condition for very high magnetocurrent observation in Alq3.