We demonstrate that organic thin film transistors (OTFTs) can act as an alternative tool for carrier mobility evaluation in
amorphous organic electronic materials. OTFT is a three terminal device which can be operated with an active layer of
film thickness thinner than 100 nm. The materials under investigation are phenylamine-based (PA) compounds, which
are amorphous hole transporting materials widely used in organic light emitting diodes (OLEDs). The field effect (FE)
mobilities of PA compounds (hole) were determined in a TFT configuration. For the case of
(1,1'biphenyl)-4,4'diamine (NPB), the FE mobility was found to be 2 × 10-5 cm2/Vs. It is about one order of
magnitude smaller than that obtained from independent time-of-flight (TOF) technique (2 x 10-4 cm2/Vs) using a thick
film of ~ 5 μm. Temperature dependent measurement was performed under temperature ranging from 235 to 360 K. The
extracted energetic disorder by means of the Gaussian Disorder Model from OTFT was 85meV, which was larger than
that of TOF (~74 meV). Similar observations were found in other PA compounds. The increase in the extracted disorder
parameter in TFT configuration was one of the origins of the discrepancy between the FE and TOF mobility. OTFTs can
be regarded as a useful tool for carrier mobility evaluation with little material consumption.
Tris(8-hydroxyquinoline) aluminum (Alq) has been widely used as the electron transporting layer as well as the green emitter layer in organic light emitting diodes (OLEDs) since it is thermally and morphologically stable to
evaporate into thin films. Alq exhibits strong green emission but its spectrum is broad (~85 nm FWHM) which results in
inferior colour purity. On the other hand, rare-earth metal ions exhibit sharp spectral band which corresponds to 5Dx-7Fx
transitions. In the case of terbium, this results in a sharp emission in green.
In this work, organic light emitting diodes based on a rare-earth metal complex [Tris(3-methyl-1-phenyl-4-
trimethyl-acetyl-5-pyrazoline) terbium III] were fabricated by thermal evaporation. The basic device structure is indium
tin oxide(ITO) / 4,4'-N,N'-dicarbazole-biphenyl (CBP) / 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) / tris(8-
hydroxyquinoline) aluminum (Alq) / Lithium Floride(LiF) / Aluminium (Al). The terbium (Tb) complex was doped into
the hole transporting material (CBP) and the electron transporting material (Alq) to investigate the effect of dopant in
different layers on the device performance. The effects of different dopant concentration on the photoluminescence (PL)
and electroluminescence (EL) emission spectra were also investigated. Sharp emission in green (545 nm) was observed
for optimum device structure and doping concentration.
We report on detailed simulations of the emission from microcavity OLEDs consisting of widely used organic materials, N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq3) as emitting and electron transporting layer. The thick silver film was considered as a top mirror, while silver or copper films on quartz substrate were considered as bottom mirrors. The electroluminescence emission spectra, electric field distribution inside the device, carrier density and recombination rate were calculated as a function of the position of the emission layer, i.e. interface between NPB and Alq3. In order to achieve optimum emission from a microcavity OLED, it is necessary to align the position of the recombination region with the antinode of the standing wave inside the cavity. Once the optimum structure has been determined, the microcavity OLED devices were fabricated and characterized. The
experimental results have been compared to the simulations and the influence of the emission region width and position on the performance of microcavity OLEDs was discussed.
Tris(8-hydroxyquinoline) aluminum (Alq3) is one of the most commonly used electron transporting and luminescent materials for organic light emitting diodes (OLEDs). It is thermally and morphologically stable to evaporate into thin films and it is a good green emitter. Due to its importance in OLEDs, the properties of Alq3 have been extensively studied. Most of the studies, however, were concentrated on the single crystals, powder or thin films of Alq3. Recently, synthesis of Alq3 nanostructures, such as nanoparticles and nanowires, has been reported. Nanostructures have been attracting increasing attention because they may have new optical, electronic, magnetic, and mechanical properties compared with those of bulk materials. In this work, we reported synthesis of Alq3 nanowires by heating Alq3 powder in a gas flow. The nanowires were grown on glass substrates which were located in the downstream. The obtained nanostructures were characterized by scanning electron microscopy (SEM) and photoluminescence (PL). The effect of substrate temperatures, fabrication system geometry (i.e. source to substrate distance), the choice of gas, and gas flow rate on the resulting nanostructures were investigated. It is found that the synthesis conditions had significant effect on the morphologies of the resulting nanostructures, but the PL showed no significant dependence on the morphology.