Gutowski, Jürgen
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Gutowski, Jürgen
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Gutowski, Jürgen
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Gutowski, Juergen
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GND
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Item-typ:Veröffentlichung, Relationship between the VOC Tuning Effect and the Interface Activation Energy Due to the Third Component Concentration in Ternary Organic Solar Cells(American chemical society, 2022-04-08); ; ; ; The open-circuit voltage (VOC) tuning effect due to the variation of the low concentration of the third component in ternary organic solar cells has been mainly attributed to interfacial phenomena. Up to date, the models reported in the literature to analyze such interfacial phenomena are based on optical characterization. In this work is proposed a different approach to study such a VOC tuning effect by using dark-current characteristics at different temperatures. Specifically, for PTB7-Th:PC71BM:ICBA-based solar cells, it is found that an increment of the third component concentration, that is, the fullerene ICBA, causes an increase in the activation energies (Ea) in an Arrhenius-type curve. This, in turn, decreases the reverse saturation current (J0) of the devices, thereby incrementing their VOC.Wissenschaftlicher ArtikelBand:5Heft:440 51 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Numerical simulation of a bilayer organic solar cell based on boron chromophore compounds as acceptors(IEEE, 2020-12-17); ; ; ; Organic solar cells fabricated with non-fullerene acceptors have proven to be a solution to reduce manufacturing costs. Besides the material selection, another way to reduce such costs is by optimizing the properties of both the materials and the interfaces which in turn would contribute to enhance the solar cells efficiency. This can be done with numerical simulations. Among non-fullerene materials, boron chromophores are relatively stable and chemically versatile compounds which have been usually used as donors in solar cells. In this work, planar solar cells based on PTB7 and boron compounds are proposed and simulated but by using the latter as acceptors. Specifically, we show the functionality of our proposed devices by analyzing the variation of both the Lowest Unoccupied Molecular Orbital (LUMO) and the influence of the non-intentional doping of the boron compounds with regard to the photovoltaic parameters of the solar cells. The properties of the materials such as the dielectric constant, energy levels, and non-intentional doping are taken from literature. We show that there are optimal values for LUMO and doping concentration to maximize the device efficiency. The causes of this behavior are analyzed using band diagram simulations.Konferenzbeitrag53 40 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Optical Properties and Carrier Dynamics in Inorganic and Hybrid Inorganic/Organic ZnO- and GaN-Based Nanowire Structures(Wiley, 2019-02-20); ; ; ; In this paper, results on the optical properties and carrier dynamics in inorganic and hybrid inorganic/organic semiconductor nanowire structures based on the ZnO and GaN material systems, obtained by the involved groups in the last years, are reviewed. First, the recombination dynamics in 3D GaN-based microrod LED structures is analyzed and discussed. In particular, the dynamics at high excitation densities close to the damage threshold of the material is studied. This is followed by a discussion of the carrier dynamics in nanowire structures functionalized with colloidal CdSe quantum dots (QDs) or carbon nanoparticles (C-Dots). Here, the nanoparticles allow for light absorption at photon energies below the bandgap of the semiconductor nanowire, and subsequent electron tunneling couples the electronic systems of the nanoparticles and the nanowires (NWs). Finally, the fabrication of nanowire/polymer core–shell structures is demonstrated and the electrical properties of n-nanowire/p-polymer hybrid junctions are studied.Wissenschaftlicher ArtikelBand:256Heft:442 58 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Excitons Bound to Defect States in Two-Dimensional (2D) MoS2(IEEE, 2021-04-29); ; ; ; In this work, the effect of atomic defects created by gallium ion irradiation on the optical properties of single-layer molybdenum disulfide is studied by means of micro-photoluminescence measurements. The induced defects give rise to an additional emission band located at about 170 meV below the free exciton. The micro-photoluminescence intensity of this defect-related emission band is found to be proportional to the defect density. The large spectral width suggests the presence of binding sites with different binding energies available for excitons that remain optically active up to 230 K.Wissenschaftlicher ArtikelBand:2038 31 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Controlled Laser-Thinning of MoS2 Nanolayers and Transformation to Amorphous MoOx for 2D Monolayer Fabrication(American chemical society, 2020-07-20); ; ; ; Laser-thinning of 2D materials such as MoS2 is a promising approach for a local reduction of the number of multilayers down to a monolayer. For a precise control of the thinning process real-time monitoring is required. In this work, short-wavelength lasers emitting at 325 or 406 nm respectively are used for laser-thinning and simultaneous Raman or photoluminescence spectroscopy of MoS2. The time evolution of the Raman and photoluminescence bands during the process shows a layer-by-layer thinning of MoS2 and a transformation into amorphous MoOx in an oxygen-containing atmosphere. In addition to the E2g1 and A1g Raman modes, the E1g, B2g1, and second-order modes are analyzed by using the 325 nm laser for excitation to achieve a more accurate determination of the number of layers. As a promising alternative, photoluminescence spectroscopy is used to monitor the thinning progress by analysis of the emission energy and intensity of the direct as well as the indirect band gap transition. Atomic force microscopy measurements show an increased total height of the laser-treated region after thinning of MoS2 due to the presence of transformed MoOx. Local micropatterning of a bilayer is also demonstrated by laser-thinning down to a monolayer at selected positions. The results show a new monitoring approach for controlled fabrication of 2D monolayers.Wissenschaftlicher ArtikelBand:3Heft:842 35 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Organoboron donor-π-acceptor chromophores for small-molecule organic solar cells(Springer, 2018-07-26); ; ; ; We introduce the use of facilely synthesizable and low-bandgap boron chromophores as donors in planar heterojunction solar cells. We show that simple changes in the compositional properties of these molecules can improve the performance of the devices. A simultaneous grafting of NO2 acceptor and N(Et2) donor groups into the molecule core causes an increase in efficiency of almost 50%. Such enhanced efficiency is mainly due to a higher photocurrent. The origin of this phenomenon is investigated.Wissenschaftlicher ArtikelBand:2942 93 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Spatially resolved luminescence properties of non- and semi-polar InGaN quantum wells on GaN microrods(IOP Publishing, 2018-08-03); ; ; ; Spatially resolved emission properties of InGaN/GaN quantum wells on the facets of microrods are analyzed by means of photoluminescence and cathodoluminescence measurements. We observe strongly localized emissions of the non- and semi-polar InGaN quantum wells from the top part of the microrods, suggesting optical emitters of high efficiency. The quantum wells are characterized by transmission electron microscopy measurements with respect to their indium composition and thickness. Those wells oriented in non- and semi-polar directions possess high In concentrations as well as low internal polarization fields which makes these directions excellent candidates for InGaN quantum well emitters. These investigations show that the applied microrod growth concept is an effective method to realize high quality InGaN quantum wells on GaN facets oriented in non- and semi-polar directions which makes optoelectronic emitters in the green gap region feasible.Wissenschaftlicher ArtikelBand:5127 21 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Numerical study of efficient ternary planar hybrid solar cells using simple boron molecules as organic compounds(Elsevier Science, 2022-10); ; ; ; Ternary solar cells have proven to be a solution to absorb more photons at different wavelengths and reduce the recombination of charge carriers. Here, we propose a new hybrid organic-inorganic ternary planar solar-cell structure using a novel boron compound. The role of this material on the performance of the device with a polymer/borinate/ZnO configuration is studied. As the donor polymer, we evaluate P3HT, PTB7, and PCPDTBT; and three boron compounds with different properties, especially concerning the bandgap and trap energy depth. To validate the experimental electrical characteristics of the borinates, first, we simulate a bilayer structure with C60, subsequently, we simulate and analyze the whole device architecture. The ternary solar cell with PTB7 and a borinate with a bandgap of 1.66 eV and a medium trap energy depth of 0.95 eV above the HOMO level exhibit the highest efficiency, i. e. 11.7%. Furthermore, we present a layer thickness optimization of the materials to reach even higher efficiencies, up to 15.15%. Finally, the effect of the magnitude of the density of trap states in the borinate on the device performance is analyzed.Wissenschaftlicher ArtikelBand:13249 67 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Understanding the open circuit voltage in organic solar cells on the basis of a donor-acceptor abrupt (p-n++) heterojunction(Elsevier Science, 2019-05-15); ; ; ; By using electrical characterization and classical solid state semiconductor device theory, we demonstrate that the open circuit voltage (Voc) in organic solar cells based on non-intentional doped semiconductors is fundamentally limited by the built-in potential (Vbi) originated at a donor-acceptor abrupt (p-n++) heterojunction in case of selective contacts. Our analysis is validated using P3HT:PCBM devices fabricated in our research group. We also demonstrate that such a result can be generalized using data already reported in literature for fullerene-based solar cells. Finally, we show that the dependence of Voc on the device contacts can be understood in terms of the potential barriers formed by the Fermi level alignment of semiconductors at the heterojunction and at the Schottky junctions.Wissenschaftlicher ArtikelBand:18450 27