Search results for "MOBILITY"
showing 10 items of 922 documents
Study of the annealing conditions and photoelectrochemical characterization of a new iron oxide bi-layered nanostructure for water splitting
2016
Iron oxide nanostructures have emerged as promising materials for being used as photocatalysts for hydrogen production due to their advantageous properties. However, their low carrier mobility and short hole diffusion length limit their efficiency in water splitting. To overcome these drawbacks, in the present study, we synthetized a new hematite (alpha-Fe2O3) bi-layered nanostructure consisting of a top nanosphere layer and a nanotubular underneath one by electrochemical anodization. Annealing parameters such as temperature, heating rate and atmosphere were studied in detail in order to determine the optimum annealing conditions for the synthetized nanostructure. The obtained new bi-layere…
Transport properties of nitrogen doped p‐gallium selenide single crystals
1996
Nitrogen doped gallium selenide single crystals are studied through Hall effect and photoluminescence measurements in the temperature ranges from 150 to 700 K and from 30 to 45 K, respectively. The doping effect of nitrogen is established and room temperature resistivities as low as 20 Ω cm are measured. The temperature dependence of the hole concentration can be explained through a single acceptor‐single donor model, the acceptor ionization energy being 210 meV, with a very low compensation rate. The high quality of nitrogen doped GaSe single crystals is confirmed by photoluminescence spectra exhibiting only exciton related peaks. Two phonon scattering mechanisms must be considered in orde…
Azatruxene‐Based, Dumbbell‐Shaped, Donor–π‐Bridge–Donor Hole‐Transporting Materials for Perovskite Solar Cells
2020
Three novel donor-π-bridge-donor (D-π-D) hole-transporting materials (HTMs) featuring triazatruxene electron-donating units bridged by different 3,4-ethylenedioxythiophene (EDOT) π-conjugated linkers have been synthesized, characterized, and implemented in mesoporous perovskite solar cells (PSCs). The optoelectronic properties of the new dumbbell-shaped derivatives (DTTXs) are highly influenced by the chemical structure of the EDOT-based linker. Red-shifted absorption and emission and a stronger donor ability were observed in passing from DTTX-1 to DTTX-2 due to the extended π-conjugation. DTTX-3 featured an intramolecular charge transfer between the external triazatruxene units and the azo…
Photosensitivity of SiO2–Al and SiO2–Na glasses under ArF (193 nm) laser
2009
Abstract Photosensitivity of SiO 2 –Al and SiO 2 –Na glass samples was probed by means of the induced optical absorption and luminescence as well as by electron spin-resonance (ESR) after irradiation with excimer-laser photons (ArF, 193 nm). Permanent visible darkening in the case of SiO 2 –Al and transient, life time about one hour, visible darkening in the case of SiO 2 –Na was found under irradiation at 290 K. No darkening was observed at 80 K for either kind of material. This investigation is dedicated to revealing the electronic processes responsible for photosensitivity at 290 and 80 K. The photosensitivity of both materials is related to impurity defects excited directly in the case …
Flexible diphenylsulfone versus rigid dibenzothiophene-dioxide as acceptor moieties in donor-acceptor-donor TADF emitters for highly efficient OLEDs
2020
DG acknowledges funding from the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/177 . This research is/was funded by the European Regional Development Fund according to the supported activity ‘ Research Projects Implemented by World-class Researcher Groups ’ under Measure No. 01.2.2-LMT-K-718 . Ministry of Science and Technology (MOST), Taiwan , Grant No. MOST 106-2923-E-155-002-MY3 . This work was also supported by the Ministry of Education and Science of Ukraine (projects no. 0117U003908 and 0118U003862 ), and by the Olle Engkvist Byggmästare foundation (contract No. 189-0223 ). The quantum-chemical calculations were performed with computational resources provided by the High Performance Comp…
Luminescence and electron transport properties of GaN and AlN layers
2001
Abstract The transport properties of free charge carriers, photo- and cathodo-luminescence (CV) in GaN and AlN films obtained by MOCVD technique on sapphire and Si substrates, are investigated. The concentration of free charge carriers in GaN is of order 10 17 – 10 19 cm −3 whereas AlN thin films are insulating. The Hall mobility of electrons are 80– 140 cm 2 / V s ). In undoped GaN films the spectral composition of CL is close to photoluminescence (PL) when excited in the region of band–band transitions. The decay time constant of the 3.44 eV UV emission attributed to the bound exciton is considerably less than 1 ns , whereas the 3.26 eV violet (VI) band shows a slow hyperbolical decay ove…
Space Charge and Carrier Trapping Effects on the Transient Photocurrents of Organic Materials Using the Time-of-Flight Technique
2007
We apply the time-of-flight (TOF) technique to study space charge and carrier trapping effects in the organic materials N,N'-diphenyl-N,N'-bis(3- methylphenyl)-1,1-biphenyl-4,4'-diamine (TPD) and tris(8-hydroxyquinolato) aluminum (Alq3). This is carried out by changing the applied electric field, the laser pulse intensity, and the repetition rate together with environmental conditions in air or in vacuum. We report for the first time, to the best of our knowledge, a clearly nondispersive electron transport in TPD due to the absence of deep traps. Conversely, Alq3 exhibits a dispersive electron transport. However, this can be partially recovered by leaving the sample in high vacuum for sever…
SURFACE EFFECTS ON THE GROWTH OF SOLUTION PROCESSED PENTACENE THIN FILMS
2008
13,6-N-Sulfinylacetamidopentacene (SAP) has been transferred on solid substrates both by water-rich environment and organic solvents without altering his chemical structure. Thermal conversion of SAP to pentacene leads to crystals showing similar features of vacuum-sublimated pentacene both in the bulk and thin-film phases. The thin-film phase is strongly affected by the substrate surface properties. Low energy Si-CH3 rich surfaces allow for the formation of compact micrometric crystals following a Volmer-Weber like growth with orientation suitable for field-effect carrier mobility. Screw dislocations along with straight edges are found on these systems as an indication of a loose interlaye…
Differently substituted benzonitriles for non-doped OLEDs
2020
DG acknowledges to the ERDF PostDoc grant No. 1.1.1.2/VIAA/1/16/177 . This research was funded by the European Regional Development Fund according to the supported activity ‘Research Projects Implemented by World-class Researcher Groups’ under Measure No. 01.2.2-LMT-K-718 .
Discotic Liquid Crystals - A New Class of Fast Photoconductors
1993
We showed for the first time that discotic liquid crystals are well suited for a new class of fast photoconducting materials. Due to their spontaneous orientation and their dynamical fluctuations in the mesophase, they show exceptionally high mobilities of 1·10−3 cm2/Vs, about two to three orders of magnitude higher than those obtained for conventional amorphous polymers. Further on, the Gaussian transport (for holes in the mesophase) is remarkable, which is characterized by the existence of a conduction band and the absence of trapping states. In contrast, the charge carrier transport in amorphous photoconductors is generally trap-dominated which limits technical properties, leading to low…