The Experts below are selected from a list of 56469 Experts worldwide ranked by ideXlab platform
Martin Pfeiffer - One of the best experts on this subject based on the ideXlab platform.
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very high efficiency and low voltage phosphorescent organic light emitting diodes based on a p i n junction
Journal of Applied Physics, 2004Co-Authors: Gufeng He, Oliver Schneider, Xiang Zhou, Martin PfeifferAbstract:Green phosphorescent organic light-emitting devices (OLEDs) employing tris(2-phenylpyridine) iridium Doped into a wide energy gap hole transport host have been studied. N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine Doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane is used as a hole injection and transport Layer, 4,7-diphenyl-1,10-phenanthroline and cesium are coevaporated as a n-Doped electron transport Layer, and an intrinsic emission Layer is sandwiched between these two Doped Layer. Such a p-i-n device features efficient carrier injection from both contacts into the Doped transport Layers and low ohmic losses in these highly conductive Layers. Thus, low operating voltages are obtained compared to conventional unDoped OLEDs. By modifying the device structure, we optimized the carrier balance in the emission Layer and at its interfaces. For the optimized device, the maximum power efficiency is 53 lm/W, and a luminance of 1000 cd/m2 is reached at 3.1 V with a power efficiency of 45 lm/W.
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non polymeric oleds with a Doped amorphous hole transport Layer and operating voltages down to 3 2 v to achieve 100 cd m2
Synthetic Metals, 2002Co-Authors: Jan Blochwitz, Martin Pfeiffer, M Hofmann, Karl LeoAbstract:Abstract We have previously shown that p-type doping of the hole injection and transport Layer of an organic light emitting diode (OLED) by co-evaporation of two molecules leads to lower operating voltages of the device. In such OLEDs, the use of a proper buffer Layer between the Doped Layer and the light emission Layer is essential to yield a high efficiency. Here, we apply the doping concept to OLEDs with a light emission Layer Doped with a fluorescent dye in order to prove that doping of the transport Layer is able to improve the optoelectronic properties of highly efficient OLEDs. The emitter Layer consists of quinacridone (QAD) Doped aluminum-tris-(8-hydroxy-quinolate) (Alq 3 ). The hole injection and transport Layer is a Starburst Layer p-type-Doped with tetrafluoro-tetracyano-quinodimethane (F 4 -TCNQ). As buffer Layer, a diamine Layer (TPD) is used. Holes are injected from untreated ITO electrons via a lithium fluoride (LiF)/aluminum cathode combination. For this OLED Layer sequence, we achieved a luminance of 100 cd/m 2 in forward direction at the lowest operating voltage ever reported for non-polymeric OLEDs (3.2–3.4 V) with a current efficiency of around 10 cd/A.
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controlled p doping of pigment Layers by cosublimation basic mechanisms and implications for their use in organic photovoltaic cells
Solar Energy Materials and Solar Cells, 2000Co-Authors: Martin Pfeiffer, Andre Beyer, B Plonnigs, A Nollau, Torsten Fritz, Derck Schlettwein, Stefan Hiller, Dieter WohrleAbstract:Abstract We present a systematic study on doping of vanadyl- and zinc-pathalocyanine by a fully fluorinated form of tetracyano-quinodimethane as an example of controlled doping of thin organic films by cosublimation of matrix and dopant. The films are characterized in situ by temperature dependent Seebeck and conductivity measurements. We observe a drastic increase of conductivity and a corresponding shift of the Fermi level towards the valence states with increasing dopant concentration. We thus conclude that doping has the potential of both reducing the series resistance and increasing the photovoltage of organic solar cells. As a first step to exploit this potential, we present two different ways of preparing diodes with rectification ratios in excess of 10 4 using Doped phthalocyanines. By adding an unDoped interLayer between the contact and the Doped Layer, we have produced diodes which work already in the strict absence of oxygen and are stable in air. To increase the efficiency of charge carrier generation in photovoltaic cells, we need to use photoactive donor–acceptor-heterojunctions. We present here first examples of pn- and pin-type heterojunctions combining p-Doped and nominally unDoped Layers.
Martin Kuball - One of the best experts on this subject based on the ideXlab platform.
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electric field reduction in c Doped algan gan on si high electron mobility transistors
IEEE Electron Device Letters, 2015Co-Authors: M J Uren, Markus Caesar, Serge Karboyan, Peter Moens, Piet Vanmeerbeek, Martin KuballAbstract:It is shown by simulation supported by experiment that a reduced surface field effect, associated with compensated deep acceptors, can occur in carbon Doped GaN-on-Si power switching AlGaN/GaN transistors, provided there is a vertical leakage path from the 2DEG to the carbon-Doped Layer. Simulations show that this effect is not present in devices using iron-Doped GaN buffers explaining the higher voltage capability of carbon-Doped devices.
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buffer transport mechanisms in intentionally carbon Doped gan heterojunction field effect transistors
Applied Physics Letters, 2014Co-Authors: M J Uren, Markus Casar, Mark Gajda, Martin KuballAbstract:Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer Layers in a carbon Doped GaN power heterojunction field effect transistor. Carbon Doped GaN and multiple Layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C Doped Layer is shown to occur by hole conduction in the valence band with activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.
M J Uren - One of the best experts on this subject based on the ideXlab platform.
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electric field reduction in c Doped algan gan on si high electron mobility transistors
IEEE Electron Device Letters, 2015Co-Authors: M J Uren, Markus Caesar, Serge Karboyan, Peter Moens, Piet Vanmeerbeek, Martin KuballAbstract:It is shown by simulation supported by experiment that a reduced surface field effect, associated with compensated deep acceptors, can occur in carbon Doped GaN-on-Si power switching AlGaN/GaN transistors, provided there is a vertical leakage path from the 2DEG to the carbon-Doped Layer. Simulations show that this effect is not present in devices using iron-Doped GaN buffers explaining the higher voltage capability of carbon-Doped devices.
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buffer transport mechanisms in intentionally carbon Doped gan heterojunction field effect transistors
Applied Physics Letters, 2014Co-Authors: M J Uren, Markus Casar, Mark Gajda, Martin KuballAbstract:Temperature dependent pulsed and ramped substrate bias measurements are used to develop a detailed understanding of the vertical carrier transport in the buffer Layers in a carbon Doped GaN power heterojunction field effect transistor. Carbon Doped GaN and multiple Layers of AlGaN alloy are used in these devices to deliver an insulating and strain relieved buffer with high breakdown voltage capability. However, understanding of the detailed physical mechanism for its operation is still lacking. At the lowest electric fields (<10 MV/m), charge redistribution within the C Doped Layer is shown to occur by hole conduction in the valence band with activation energy 0.86 eV. At higher fields, leakage between the two-dimensional electron gas and the buffer dominates occurring by a Poole-Frenkel mechanism with activation energy ∼0.65 eV, presumably along threading dislocations. At higher fields still, the strain relief buffer starts to conduct by a field dependent process. Balancing the onset of these leakage mechanisms is essential to allow the build-up of positive rather than negative space charge, and thus minimize bulk-related current-collapse in these devices.
I Usatii - One of the best experts on this subject based on the ideXlab platform.
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silicon oxide based n Doped Layer for improved performance of thin film silicon solar cells
Applied Physics Letters, 2010Co-Authors: Paola Delli Veneri, L V Mercaldo, I UsatiiAbstract:We propose the use of n-Doped silicon oxide as alternative n-Layer in thin film Si p-i-n solar cells. By varying input gas ratios, films with a wide range of optical and electrical properties are obtained. Applying these Layers in solar cells, good electrical and optical properties are demonstrated. A relative efficiency increase up to 13.6% has been observed on the cells adopting a simple Ag back contact. A similar spectral response as with the cell with standard n-Layer plus ZnO/Ag back contact is obtained. The deposition of a buffer Layer at the back contact can therefore be avoided.
Reinhard Carius - One of the best experts on this subject based on the ideXlab platform.
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study of detached back reflector designs for thin film silicon solar cells
Physica Status Solidi-rapid Research Letters, 2012Co-Authors: Etienne Moulin, Ulrich W Paetzold, Joachim Kirchhoff, Andreas Bauer, Reinhard CariusAbstract:We present a precise and flexible method to investigate the impact of diverse detached reflector designs on the optical response of p–i–n thin-film silicon solar cells. In this study, the term detached reflectors refers to back reflectors that are separated from the silicon Layers by an intermediate rear dielectric of several micrometers. Based on the utilization of a highly conductive n-Doped Layer and a local electrical contact scheme, the method allows the use of non-conductive rear dielectrics such as air or transparent liquids. With this approach, diverse combinations of back reflector and rear dielectric can be placed behind the same solar cell, providing a direct evaluation of their impact on the device performance. We demonstrate the positive effect of a rear dielectric of low refractive index on the light trapping and compare the performance of solar cells with an air/Ag and a standard ZnO/Ag back reflector design. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)