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Dissertations / Theses on the topic 'Optoelectronic devices'
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1
Thompson, Paul. "II-VI optoelectronic devices." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/726.
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Vaughan, John. "Optoelectronic devices for spectrochemical sensing." Thesis, University of Manchester, 2005. https://www.research.manchester.ac.uk/portal/en/theses/optoelectronic-devices-for-spectrochemical-sensing(a6ea9f13-f235-4920-b63e-51e64a402327).html.
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Higgins, Steven Paul. "Computer simulation of optoelectronic devices." Thesis, University of Essex, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413634.
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Shapira, Ofer Ph D. Massachusetts Institute of Technology. "Optical and optoelectronic fiber devices." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40511.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 111-119).
The ability to integrate materials with disparate electrical, thermal, and optical properties into a single fiber structure enabled the realization of fiber devices with diverse and complex functionalities. Amongst those, demonstrated first in our work, are the surface-emitting fiber laser, the hollow-core fiber amplifier, the thermally self-monitored high-power transmission fiber device, and the photo-detecting fiber-web based imaging system. This work presents the design, analysis, and characterization of those devices. It opens with a study of the transmission properties of the multimode hollow-core, photonic bandgap fiber constructed of a periodic multilayer cladding. A defect is then introduced into one of the cladding layers and the interaction between core and defect modes is investigated. The second chapter addresses the experimental problem encountered in many multimode waveguide applications: how to extract, and to some extent to control, the modal content of the field at the output of a waveguide. We developed a non-interferometric approach to achieve mode decomposition based on a modified phase retrieval algorithm that can yield the complete vectorial eigenmode content of any general waveguiding structure and demonstrated its validity experimentally. In the third chapter an active material is introduced into the hollow-core to form a surface-emitting fiber laser. A unique azimuthally anisotropic optical wave front results from the interplay between the cylindrical resonator, the anisotropic gain medium, and the linearly polarized axial pump. We show that the direction and polarization of the wave front are directly controlled by the pump polarization.
(cont.) In the last two chapters, a new type of fiber is presented, constructed of semiconducting, insulating, and conducting materials, which enables the integration of semiconductor devices into the fiber structure. In the first we demonstrate a fiber comprised of an optical transmission element designed for the transport of high power radiation and multiple thermal-detecting elements encompassing the hollow core for distributed temperature monitoring and real-time failure detection. In the second, we demonstrate optical imaging using large-area, three-dimensional optical-detector arrays, built from one-dimensional photodetecting optoelectronic fibers. Lensless imaging of an object is achieved using a phase retrieval algorithm.
by Ofer Shapira.
Ph.D.
5
Martins, Emiliano. "Light management in optoelectronic devices." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/6133.
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This thesis presents studies on light management in optoelectronic devices. The broad aim of the thesis is to improve the efficiency of optoelectronic devices by optimised light usage. The studies emphasise the design and fabrication of nanostructures for optimised photon control. A key hypothesis guiding the research is that better designs can be achieved by ab initio identification of their desired Fourier properties. The specific devices studied are organic Distributed Feedback (DFB) lasers, organic solar cells and silicon solar cells. The impact of a substructured grating design capable of affording unprecedented control over the balance between feedback and output coupling in DFB organic lasers was investigated both experimentally and theoretically. It was found experimentally that such gratings can halve the threshold of organic DFB lasers. The reduction in the laser threshold is associated with reduced output coupling and higher feedback provided by the substructured gratings. The possibility of improving the efficiency of organic solar cells by trapping light into the absorbing medium was investigated. It was found that the low refractive index of the organic gain medium compromises the light trapping performance. It was found that strong absorption enhancement, however, can be achieved using plasmonic nanostructures. Finally, a novel design concept for light trapping in silicon solar cells is proposed. This design takes advantage of grating structures with long periods that are capable of providing broad-band light trapping, which is an important requirement for silicon solar cells. The design is based on a supercell that enables better light injection through manipulation of the grating's Fourier properties. The design idea leads to the formation of quasi-random nanostructures that afford great versatility for photon control. Strong light trapping was achieved and characterised both theoretically and experimentally.
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Li, Guangru. "Nanostructured materials for optoelectronic devices." Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/263671.
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This thesis is about new ways to experimentally realise materials with desired nano-structures for solution-processable optoelectronic devices such as solar cells and light-emitting diodes (LEDs), and examine structure-performance relationships in these devices. Short exciton diffusion length limits the efficiency of most exciton-based solar cells. By introducing nano-structured architectures to solar cells, excitons can be separated more effectively, leading to an enhancement of the cell’s power conversion efficiency. We use diblock copolymer lithography combined with solvent-vapour-assisted imprinting to fabricate nano-structures with 20-80 nm feature sizes. We demonstrate nanostructured solar cell incorporating the high-performance polymer PBDTTT-CT. Furthermore, we demonstrated the patterning of singlet fission materials, including a TIPS-pentacene solar cell based on ZnO nanopillars. Recently perovskites have emerged as a promising semiconductor for optoelectronic applications. We demonstrate a perovskite light-emitting diode that employs perovskite nanoparticles embedded in a dielectric polymer matrix as the emissive layer. The emissive layer is spin-coated from perovskite precursor/polymer blend solution. The resultant polymer-perovskite composites effectively block shunt pathways within the LED, thus leading to an external quantum efficiency of 1.2%, one order of magnitude higher than previous reports. We demonstrate formations of stably emissive perovskite nanoparticles in an alumina nanoparticle matrix. These nanoparticles have much higher photoluminescence quantum efficiency (25%) than bulk perovskite and the emission is found to be stable over several months. Finally, we demonstrate a new vapour-phase crosslinking method to construct full-colour perovskite nanocrystal LEDs. With detailed structural and compositional analysis we are able to pinpoint the aluminium-based crosslinker that resides between the nanocrystals, which enables remarkably high EQE of 5.7% in CsPbI3 LEDs.
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Dibos, Alan. "Nanofabrication of Hybrid Optoelectronic Devices." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17463975.
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The material requirements for optoelectronic devices can vary dramatically depending on the application. Often disparate material systems need to be combined to allow for full device functionality. At the nanometer scale, this can often be challenging because of the inherent chemical and structural incompatibilities of nanofabrication. This dissertation concerns the integration of seemingly dissimilar materials into hybrid optoelectronic devices for photovoltaic, plasmonic, and photonic applications. First, we show that combining a single strip of conjugated polymer and inorganic nanowire can yield a nanoscale solar cell, and modeling of optical absorption and exciton diffusion in this device can provide insight into the efficiency of charge separation. Second, we use an on-chip nanowire light emitting diode to pump a colloidal quantum dot coupled to a silver waveguide. The resulting device is an electro-optic single plasmon source. Finally, we transfer diamond waveguides onto near-field avalanche photodiodes fabricated from GaAs. Embedded in the diamond waveguides are nitrogen vacancy color centers, and the mapping of emission from these single-photon sources is demonstrated using our on-chip detectors, eliminating the need for external photodetectors on an optical table. These studies show the promise of hybrid optoelectronic devices at the nanoscale with applications in alternative energy, optical communication, and quantum optics.Engineering and Applied Sciences - Applied Physics
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Tan, Eugene. "Design, fabrication and characterization of N-channel InGaAsP-InP based inversion channel technology devices (ICT) for optoelectronic integrated circuits (OEIC), double heterojunction optoelectronic switches (DOES), heterojunction field-effect transistors (HFET), bipolar inversion channel field-effect transistors (BICFET) and bipolar inversion channel phototransistors (BICPT)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0006/NQ42767.pdf.
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Kim, Yong Hyun. "Alternative Electrodes for Organic Optoelectronic Devices." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113279.
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This work demonstrates an approach to develop low-cost, semi-transparent, long-term stable, and efficient organic photovoltaic (OPV) cells and organic light-emitting diodes (OLEDs) using various alternative electrodes such as conductive polymers, doped ZnO, and carbon nanotubes. Such electrodes are regarded as good candidates to replace the conventional indium tin oxide (ITO) electrode, which is expensive, brittle, and limiting the manufacturing of low-cost, flexible organic devices. First, we report long-term stable, efficient ITO-free OPV cells and transparent OLEDs based on poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes by using a solvent post-treatment or a structure optimization. In addition, a high performance internal light out-coupling system for white OLEDs based on PEDOT:PSS-coated metal oxide nanostructures is developed. Next, we demonstrate highly efficient ITO-free OPV cells and OLEDs with optimized ZnO electrodes doped with alternative non-metallic elements. The organic devices based on the optimized ZnO electrodes show significantly improved efficiencies compared to devices with standard ITO. Finally, we report semi-transparent OPV cells with free-standing carbon nanotube sheets as transparent top electrodes. The resulting OPV cells exhibit very low leakage currents with good long-term stability. In addition, the combination of various kinds of bottom and top electrodes for semi-transparent and ITO-free OPV cells is investigated. These results demonstrate that alternative electrodes-based OPV cells and OLEDs have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturingDie vorliegende Arbeit demonstriert einen Ansatz zur Verwirklichung von kostengünstigen, semi-transparenten, langzeitstabilen und effizienten Organischen Photovoltaik Zellen (OPV) und Organischen Leuchtdioden (OLEDs) durch die Nutzung innovativer Elektrodensysteme. Dazu werden leitfähige Polymere, dotiertes ZnO und Kohlenstoff-Nanoröhrchen eingesetzt. Diese alternativen Elektrodensysteme sind vielversprechende Kandidaten, um das konventionell genutzte Indium-Zinn-Oxid (ITO), welches aufgrund seines hohen Preises und spröden Materialverhaltens einen stark begrenz Faktor bei der Herstellung von kostengünstigen, flexiblen, organischen Bauelementen darstellt, zu ersetzten. Zunächst werden langzeitstabile, effiziente, ITO-freie Solarzellen und transparente OLEDs auf der Basis von Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) Elektroden beschrieben, welche mit Hilfe einer Lösungsmittel-Nachprozessierung und einer Optimierung der Bauelementstruktur hergestellt wurden. Zusätzlich wurde ein leistungsfähiges, internes Lichtauskopplungs-System für weiße OLEDs, basierend auf PEDOT:PSS-beschichteten Metalloxid-Nanostrukturen, entwickelt. Weiterhin werden hoch effiziente, ITO-freie OPV Zellen und OLEDs vorgestellt, bei denen mit verschiedenen nicht-metallischen Elementen dotierte ZnO Elektroden zur Anwendung kamen. Die optimierten ZnO Elektroden bieten im Vergleich zu unserem Laborstandard ITO eine signifikant verbesserte Effizienz. Abschließend werden semi-transparente OPV Zellen mit freistehenden Kohlenstoff-Nanoröhrchen als transparente Top-Elektrode vorgestellt. Die daraus resultierenden Zellen zeigen sehr niedrige Leckströme und eine zufriedenstellende Stabilität. In diesem Zusammenhang wurde auch verschiedene Kombinationen von Elektrodenmaterialen als Top- und Bottom-Elektrode für semi-transparente, ITO-freie OPV Zellen untersucht. Zusammengefasst bestätigen die Resultate, dass OPV und OLEDs basierend auf alternativen Elektroden vielversprechende Eigenschaften für die praktische Anwendung in der Herstellung von effizienten, kostengünstigen, flexiblen und semi-transparenten Bauelement besitzen
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Yiu, Wai-kin, and 姚偉健. "Plasmonic enhancement of organic optoelectronic devices." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/211120.
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Plasmonics can be applied in a wide range of optoelectronic devices and it is induced by the interaction between incident light and conduction electrons. Resonance is induced by matching the photon energy and the frequency of electrons, which can cause the surface charge distribution and strengthens the electromagnetic field. Generally, plasmonics can be classified into surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR). SPR is the propagating wave, which occurs at interface between the dielectric and metal. LSPR is the non-propagating wave, which is the interaction between the metal nanoparticles (NPs) and incident light when the NP size is smaller than the light wavelength. In this thesis, plasmonic enhancement is studied to improve the performance of organic solar cells (OSCs) and light emission of organic semiconductors.
OSCs are low cost, light weight, flexibility, and solution process ability at room temperature. Short exciton diffusion length limits the thickness of active layer, which causes low photon absorption and consequently low current generation. In this part, gold nanoparticles (Au NPs) are blended into OSCs to enhance photovoltaic performance. Au NPs can induce the localized surface plasmon resonance (LSPR) which enhances the light absorption due to electromagnetic field generation. Also, light can be trapped by scattering to increase the optical path and thus enhance the charge carrier generation.
Film structure and 1D nanostructure of organic semiconductor are studied by their photoluminescence (PL) intensity. Generally, the PL intensity can be enhanced by SPR. Excitation energy can induce the surface plasmon (SP) instead of photon, which can amplify the spontaneous emission and stimulated emission. Compared to thin films, 1D organic structures achieve higher PL enhancement because they can trap the light more efficiently by Fabry-Pérot cavity. Different morphologies of organic semiconductor are synthesized and it is found that hexagonal plates can obtain better PL enhancement because of the Fabry-Pérot cavity mode.published_or_final_version
Physics
Master
Master of Philosophy
11
Congreve, Daniel Norbert. "Excitonic spin engineering in optoelectronic devices." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99816.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 133-144).
Despite decades of research, solar cell efficiencies struggle to get higher than 25%. This is due to two fundamental losses in the device: thermalization of high energy photons and transmission of low energy photons. In this work, we demonstrate efforts to improve both these losses, which, when fully realized, could increase power efficiencies to 35% or higher. First, we utilize singlet exciton fission as a downconverting layer. Singlet exciton fission is a process in which a single high energy exciton fissions into two excitons of half the energy. Here, we first demonstrate the potential of singlet fission in an all-organic solar cell. We measure an EQE as high as 109%, breaking the conventional limit of 100%. We utilize the magnetic field effect of fission to characterize and quantize the fission yield in these devices, demonstrating that an increase in absorption should lead to even higher EQE values. Next, we utilize an optical light trapping scheme to increase the absorption, driving the EQE as high as 126% with no external optics. Finally, we demonstrate the ability to orthogonalize singlet fission from the normal OPV functions such as absorption and charge transport with a small interfacial layer of a fission material. With the efficiency of singlet fission established, we then demonstrate how it can be utilized by building an optical downconverter with tetracene as the fission material and PbS colloidal nanocrystals as the acceptor. We demonstrate that low energy excitons generated in the fission material transfer to the nanocrystal with 90% efficiency before fluorescing. This fluorescence will be able to transfer energy to inorganic solar cells such as silicon. To combat the transmission loss, we turn to the reverse process of singlet fission: triplet-triplet annihilation. We utilize colloidal nanocrystals as the sensitizer and rubrene as the annihilator. The use of colloidal nanocrystals as the sensitizer allows us to minimize energetic loss and extend deeper into the infrared as compared to state of the art devices, while allowing for facile construction of a solid state geometry. We characterize this process and demonstrate the potential it holds for future solar cells. Finally, we characterize the charge transfer state in organic solar cells. We demonstrate that intersystem crossing plays a key role, defining device performance and recombination. We further show that these states are mobile and can diffuse via an 'inchworm' hopping motion.
by Daniel Norbert Congreve.
Ph. D.
12
Kinner, Lukas. "Flexible transparent electrodes for optoelectronic devices." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22419.
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Transparente Elektroden (TE) sind unverzichtbar in modernen optoelektronischen Bauelementen. Die derzeitig am häufigsten verwendete TE ist Indium Zinn Oxid (ITO). Aufgrund der Nachteile von ITO setzt sich die vorliegende Arbeit mit ITO-Alternativen auseinander. Zwei Ansätze werden in dieser Arbeit untersucht. Der erste Ansatz beruht auf Dielektrikum/Metall/Dielektrikum (DMD) Filmen, im zweites Ansatz werden Silber Nanodrähten (NW) als TE untersucht. Im ersten Ansatz wurden DMD Elektroden auf Glas und Polyethylenterephthalat (PET) fabriziert. Eine Kombination von gesputterten TiOx/Ag/AZO Schichten lieferte die höchste jemals gemessene Transmission und Leitfähigkeit für eine Elektrode auf Glas und PET. Eine durchschnittliche Transmission größer als 85 % (inklusive Substrat) im Bereich von 400-700 nm und einen Schichtwiderstand von unter 6 Ω/sq wurden erreicht. Um die Leistung der TiOx/Ag/AZO Elektrode in einem Bauteil zu überprüfen, wurde sie in einer organischen Licht emittierenden Diode (OLED) implementiert. Die DMD-basierten OLEDs erreichten eine 30 % höhere Strom Effizienz auf Glas und eine 260 % höhere Strom Effizienz auf PET im Unterschied zu den ITO-basierten Bauteilen. Im zweiten Ansatz zur Realisierung flexibler transparenter Elektroden wurden NWs diskutiert. Die Implementierung von Nanodrähten in lösungsprozessierten organischen Licht emittierenden Dioden weißt noch immer zwei große Hürden auf: hohe Rauigkeit der Nanodrahtfilme und Wärmeempfindlichkeit von PET. Um die Rauigkeit zu verkleinern und gleichzeitig die Stabilität zu erhöhen werden zunächst die Nanodrähte in ein UV-härtendes Polymer eingebettet. Es wird eine Transmission von bis zu 80 % (inklusive Substrat) und ein Schichtwiderstand von 13 Ω/sq erreicht. Gleich wie bei den DMD Elektroden wurden auch NW Elektroden in eine OLED implementiert. Die Bauteile zeigten eine größere Flexibilität, Leitfähigkeit und Luminanz als die PET/ITO Referenzen während die selbe Leistungseffizienz erreicht wurde.Transparent electrodes (TEs) are a key element in optoelectronics. TEs assure simultaneous light interaction with the active device layers and efficient charge carrier injection or extraction. The most widely used TE in today’s industry is indium tin oxide (ITO). However, there are downsides to the use of ITO. The scope of this thesis is to discuss alternatives to ITO. Two main approaches are examined in this thesis - one approach is based on using dielectric/metal/dielectric (DMD) films and the other is based on using silver nanowire (NW) films. For the first approach, a combination of sputtered TiOx/Ag/AZO was found to yield the highest transmittance and conductivity ever reported for an electrode on PET with an average transmittance larger than 85 % (including the substrate) in the range 400-700 nm and sheet resistance below 6 Ω/sq. To test the device performance of TiOx/Ag/AZO, DMD electrodes were implemented in organic light emitting diodes (OLEDs). DMD-based devices achieve up to 260 % higher efficacy on PET, as compared to the ITO-based reference devices. As a second approach, NWs were investigated. The implementation of silver nanowires as TEs in solution processed organic light emitting diodes still faces two major challenges: high roughness of nanowire films and heat sensitivity of PET. Therefore, within this thesis, an embedding process with different variations is elaborated to obtain highly conductive and transparent electrodes of NWs on flexible PET substrates. The NWs are embedded into a UV-curable polymer, to reduce the electrode roughness and to enhance its stability. A a transmittance of 80 % (including the substrate) and sheet resistance of 13 Ω/sq is achieved.
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Akyol, Fatih. "N-Polar III-Nitride Optoelectronic Devices." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1307562902.
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Squillaci, Marco. "Supramolecular engineering of optoelectronic sensing devices." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAF051/document.
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Cette thèse explore l’utilisation des principes de la chimie supramoléculaire afin de fabriquer des dispositifs senseurs de gaz novateurs et à haute performance, avec une lecture (opto)-électronique. Parmi les différentes sections, divers échafaudages tels que des réseaux hybrides bi- et tridimensionnels de particules d’or et des nanofibres supramoléculaires sont utilisés comme matériaux actifs pour la détection quantitative de l’humidité. Au sein de la dernière section, des couches 2D d’oxyde de graphène sont fabriquées par exposition à un laser IR, puis comme validation de principe, exploitées comme matériau actif pour la détection d’ozone à une concentration ppm. Chacun des échafauds présentés est basé sur un mécanisme de transduction différent, mais dans tous les cas, les interactions entre récepteurs et analytes sont basés sur des liaisons dynamiques non covalentesThis thesis explores the use of supramolecular chemistry principles to fabricate novel and high performances gas sensing devices, featuring (opto)-electronic readouts. Within the different sections, diverse scaffolds such as 2D and 3D hybrid networks of gold nanoparticles and 1D supramolecular nanofibers are exploited as active materials for the quantitative detection of environmental humidity. In the last section, 2D layers of reduced graphene oxide are fabricated by IR laser exposure and, as a proof-of-concept application, they are exploited as active materials for the detection of ozone in ppm concentration. Each of the presented scaffolds rely on a different transduction mechanism but, in all the cases, the interactions between the receptors and the analytes are based on dynamic non-covalent bonds
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Haralson, Joe Nathan II. "Design, analysis, and macroscopic modeling of high speed photodetectors emphasizing the joint opening effect avalanche photodiode and the lateral P-I-N photodiode." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/14940.
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Ho, Kai Wai. "Evaluation and characterization of efficient organic optoelectronic materials and devices." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/816.
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With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.
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Ho, Ka Wai. "Evaluation and characterization of efficient organic optoelectronic materials and devices." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/873.
Full textAbstract:
With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.
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Kwong, Chung-yin Calvin. "Improving the performance of organic optoelectronic devices by optimizing device structures." Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B31452693.
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Kwong, Chung-yin Calvin, and 鄺頌賢. "Improving the performance of organic optoelectronic devices by optimizing device structures." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B31452693.
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Tan, Zhi Kuang. "Interfacial energetics control for efficient optoelectronic devices." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708767.
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Tseng, Chun-Lung. "Development of III-V nitride optoelectronic devices." Thesis, University of Bath, 2003. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275785.
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Oey, Ching-ching. "Organic-inorganic nanocomposites for organic optoelectronic devices." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B35321222.
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Cheetham, Kieran James. "GaInAsSbP alloys for mid-infrared optoelectronic devices." Thesis, Lancaster University, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618809.
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The GaInAsSbP pentanary system has been utilised to grow epilayers on InAs substrates using Liquid Phase Epitaxy, and used to form the basis of. optoelectronic devices in the technologically important Mm spectral range (3-5 μm). The photoluminescence spectra of a single epilayer confirmed that the dominant radiative recombination mechanism was band-to-band in the pentanary layer. XRD analysis indicated the epilayers did not suffer from spinodal decomposition, and SEM and SIMS confirmed the layers were flat and abrupt. Raman spectroscopy was carried out over a wide range of lattice-matched InAsSbP compositions for the first time, before a further study on GaInAsSbP. Binary-like optical phonon signals were identified, and their position was found to directly relate to the composition of the alloy. Phonon signals resulting from alloy disorder were identified in the Raman spectra, which provides a valuable tool for future work on determining crystal quality. Prototype mesa diode devices were fabricated using wet etching with the addition of an InAsSbP window layer. Uncooled photodetectors were found to operate at room temperature, limited by diffusion current. Thermophotovoltaic cells using the same structure, designed for use with comparatively low temperature heat sources, were found to have a 33% fill factor. This is the first report of a pentanary alloy used for such an application. The corresponding photoresponse spectra exhibited two peaks, attributed to recombination in both the window layer and active region. Room temperature LEDs were demonstrated, operating with a 50% duty cycle, with their emission peaking at ~3.75 μm. The analysis of the excitation dependent electroluminescence allowed the electron effective mass of 0.018 mo to be calculated for the GaInAsSbP alloy. The devices were found to be limited by CHCC Auger recombination, even though the CHSH mechanism was suppressed by increasing the spin-orbit split-off band, as confirmed by high pressure measurements. The bandgap dependence of GalnAsSbP on pressure was found to be 10.7 meV/khar, which is believed to be the first such investigation for a III-v pentanary alloy. Multi-ring structures v/ere fabricated and current crowding effects were investigated. It was found that by employing multiple rings, rather than spot contacts, there was an improvement in the current spreading. and hence the output of the device. When only the outer-most contact was energised the current crowding under the contact was sufficient to facilitate whispering gallery modes. Lasing was achieved at 4K with drive currents of >300 mA, peaking at 3.3 μm.
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Oey, Ching-ching, and 黃晶晶. "Organic-inorganic nanocomposites for organic optoelectronic devices." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B35321222.
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DEMENICIS, LUCIENE DA SILVA. "TRANSMISSION LINE TRANSFORMER FOR HIGHSPEED OPTOELECTRONIC DEVICES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5576@1.
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ERICSSON DO BRASILA utilização de transformadores de impedância banda larga possibilita o acoplamento de forma eficiente das linhas convencionais de 50 (ômegas) dos sistemas de alta freqüência aos componentes optoeletrônicos de alta velocidade de baixa impedância, tais como lasers semicondutores (tipicamente com 3 a 5 (ômegas) de resistência de entrada). Uma das principais restrições para a realização de um transformador de impedância planar para uso em sistemas de comunicações ópticas é a sua dimensão física. A fim de se obter um transformador de impedância compacto, de dimensões compatíveis com às dos dispositivos optoeletrônicos, foram analisadas diferentes configurações. Inicialmente foi analisada a configuração coplanar (CPW) utilizando substrato de altíssima constante dielétrica. Devido às limitações encontradas nesta configuração, são propostas, aqui, duas outras soluções. As duas novas configurações propostas associam ao substrato bulk convencional de alumina, filmes de elevada constante dielétrica. Foi desenvolvida uma técnica para caracterizar a constante dielétrica e as perdas dos filmes especialmente fabricados para este trabalho. As análises teóricas mostraram que as configurações propostas apresentam desempenho muito superior ao desempenho das configurações convencionais CPW. Foi implementado o transformador de impedância utilizando uma das soluções propostas e seu desempenho foi avaliado experimentalmente.
Wide-band transmission line impedance transformer enables efficient coupling of 50 (ômegas) transmission line circuits to low impedance high-speed optoelectronic components such as semiconductor lasers (typically with input resistance of 3 to 5 [ômegas]). The physical dimensions of the planar transmission line transformer have to be properly chosen to allow its use in optical communication systems. In order to design a high performance impedance transformer with physical dimensions compatible with optoelectronic components, several possibilities were investigated. A CPW configuration with very high dielectric constant bulk substrate has been analyzed. Simulations have shown some limitations in the performance of this configuration. Then, two new configurations were introduced. Both configurations are obtained using high dielectric constant films and alumina bulk substrate. A new technique has been developed in order to characterize the dielectric constant and the losses of the films specially made for this thesis. Simulations have shown that the performance of both new configurations is much better than the conventional CPW configuration performance. The planar transmission line impedance transformer has been constructed using a new configuration and its performance has been experimentally evaluated.
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Marley, Elisabeth Anne. "The development of InP-based optoelectronic devices." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11022.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 105-106).
by Elisabeth Anne Marley.
M.S.
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Kumpatla, Srinivasarao. "Optoelectronic devices and packaging for information photonics." Thesis, Heriot-Watt University, 2009. http://hdl.handle.net/10399/2271.
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This thesis studies optoelectronic devices and the integration of these components onto optoelectronic multi chip modules (OE-MCMs) using a combination of packaging techniques. For this project, (1×12) array photodetectors were developed using PIN diodes with a GaAs/AlGaAs strained layer structure. The devices had a pitch of 250μm, operated at a wavelength of 850nm. Optical characterisation experiments of two types of detector arrays (shoe and ring) were successfully performed. Overall, the shoe devices achieved more consistent results in comparison with ring diodes, i.e. lower dark current and series resistance values. A decision was made to choose the shoe design for implementation into the high speed systems demonstrator. The (1x12) VCSEL array devices were the optical sources used in my research. This was an identical array at 250μm pitch configuration used in order to match the photodetector array. These devices had a wavelength of 850nm. Optoelectronic testing of the VCSEL was successfully conducted, which provided good beam profile analysis and I-V-P measurements of the VCSEL array. This was then implemented into a simple demonstrator system, where eye diagrams examined the systems performance and characteristics of the full system and showed positive results. An explanation was given of the following optoelectronic bonding techniques: Wire bonding and flip chip bonding with its associated technologies, i.e. Solder, gold stud bump and ACF. Also, technologies, such as ultrasonic flip chip bonding and gold micro-post technology were looked into and discussed. Experimental work implementing these methods on packaging the optoelectronic devices was successfully conducted and described in detail. Packaging of the optoelectronic devices onto the OEMCM was successfully performed. Electrical tests were successfully carried out on the flip chip bonded VCSEL and Photodetector arrays. These results verified that the devices attached on the MCM achieved good electrical performance and reliable bonding. Finally, preliminary testing was conducted on the fully assembled OE-MCMs. The aim was to initially power up the mixed signal chip (VCSEL driver), and then observe the VCSEL output.
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Xia, Yajun. "Polymeric optoelectronic devices made by inkjet printing." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613791.
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Davis, Nathaniel J. L. K. "Applications of spectral management in optoelectronic devices." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/263670.
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The application and efficiency of optoelectronic devices depends on the ability to control the absorption and emission processes of photons in semiconductors. This thesis looks at three different applications of spectral management across a broad range of optoelectronic devices: photovoltaics (PVs), luminescent solar concentrators (LSCs) and light-emitting diodes (LEDs). Multiple excitation generation (MEG) – a process in which multiple charge-carrier pairs are generated from a single optical excitation - is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley-Queisser limit. Here we present solar cells fabricated from PbSe nanorods which show external quantum efficiencies exceeding 100 %. This demonstrates the potential for substantial improvements in PV device performance due to MEG. Through spatial and spectral concentration, LSCs have the potential to reduce the cost of photovoltaic energy production and are attractive prospects for photobioreactors and building-integrated applications. Here we introduce versatile star-shaped donor-acceptor molecules based on a central BODIPY acceptor with oligofluorene donor side units. We perform comprehensive device measurements and Monte Carlo ray tracing simulations of LSCs. We find that the measured structures permit waveguide propagation lengths on a par with state-of-the-art nanocrystalline emitters, while proposed hypothetical structures can be seen as viable candidates for photobioreactor and energy production roles and should be synthesized. The efficiency of nanocrystal-based LEDs is inherently limited by the types of crystals used. Cesium lead halide perovskite nanocrystals exhibit photoluminescence quantum efficiencies approaching 100%. However, due to the large surface areas and anion mobility halogen exchange between perovskite nanocrystals of different compositions occurs rapidly, limiting applications. Here, we report significantly reduced halide exchange between chloride and iodide CsPbX3 (X= Cl, I) perovskite nanocrystals. We investigate perovskite-based multi-crystal component samples and their resulting optical and electrical interactions in bulk heterojunction LEDs. Efficient photon reabsorption from CsPbCl3 to CsPbI3 nanocrystals was found to improve LED device performance.
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Vukmirovic, Nenad. "Physics of intraband quantum dot optoelectronic devices." Thesis, University of Leeds, 2007. http://etheses.whiterose.ac.uk/1590/.
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In last two decades, semiconductor nanostructures, such as quantum wells, wires and dots, have been recognised as sources and detectors of radiation in the mid- and far-infrared region of the spectrum. Much of a success has been obtained with quantum well based intraband devices, such as quantum cascade lasers and quantum well infrared photodetectors. However due to longer carrier lifetimes in quantum dots, it is expected that optoelectronic devices based on intraband transitions in self-assembled quantum dots would have superior performance to their quantum well counterparts. In order to fully exploit this prospect, appropriate theoretical models describing electronic, optical and transport properties of the active region of these devices need to be developed, which was the subject of this thesis. It was shown how symmetry of the dot shape can be exploited to efficiently calculate the energy levels within the framework of the multiband envelope function method. The implementation of the method in the plane wave representation of the Hamiltonian eigenvalue problem and the results of its application to square based pyramidal InAs/GaAs quantum dots and hexagonal III-nitride quantum dots were given. A semiclassical model of intraband carrier dynamics in quantum dots was then developed and applied to design an optically pumped long wavelength mid-infrared laser based on intersublevel transitions in InAs/GaAs quantum dots. Two orders of magnitude lower pumping flux was predicted than in similar quantum well based devices. Next, simulations of the optical absorption spectrum in the existing quantum dot infrared photodetector structures were performed. A special emphasis was put into quantum dots-in-a-well structures and explanation of the effect of well width on the detection wavelength. A theory of transport in quantum dot infrared photodetectors starting from the energy levels and wavefunctions obtained by solving the envelope Hamiltonian, yielding as output the device characteristics such as dark current and responsivity, was then developed. The comparison with experimental data available in the literature was made, yielding a good agreement. Finally, the theory of electron transport through arrays of closely stacked quantum dots, where coherent and polaronic effects become important, therefore requiring the treatment within the formalism of the nonequilibrium Green's functions, rather than the semiclassical approach, was presented. A design of a structure promising to act as a terahertz quantum dot cascade laser was given.
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Sammito, Davide. "Integration of plasmonic gratings into optoelectronic devices." Doctoral thesis, Università degli studi di Trieste, 2013. http://hdl.handle.net/10077/8578.
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2011/2012ABSTRACT This thesis deals with the control of light absorption in semiconductor devices by the plasmonic resonances of periodically arranged metallic nanostructures integrated on them. Metallic gratings support propagating (SPP) and localized (LSP) plasmonic excitations and surface plasmons-related phenomena, like Extraordinary Optical Transmission (EOT) and plasmonic band gaps, as well as conventional diffraction effects. We combine all the optical resonances outlined to tune the incoupling and distribution of incident photons in the absorbing semiconductor substrate. In particular we consider the application of these concepts to two typologies of optoelectronic devices: photovoltaic solar cells and phototransistors. In the case of photovoltaic devices the objective is to increase the energy conversion efficiency by enhancing light harvesting and re-shaping the absorption profile, in order to improve the collection of photo-generated charge carriers. We begin analyzing a case study, a one-dimensional lamellar grating placed on a silicon substrate, by numerical optical simulations. The aim is to find the coupling conditions of the resonances supported, by designing the geometric parameters of the nanostructures, and showing their impact on the generation profile. These findings are then applied for light trapping purpose to two realistic solar cell layouts. SPP and LSP resonances are able to provide high near field magnification and effectively enhance the absorption of ultrathin organic solar cells. On the other hand, EOT coupled to diffraction orders are more suited to wafer-based Si cells. Then we present the fabrication process developed to realize the designed nanostructures over the large surface area of Si photovoltaic devices. By experiments and simulation we show that an improvement of Internal Quantum Efficiency can be obtained compared to unpatterned devices. Concerning the phototransistors, the aim is use them as compact and scalable biosensors by integrating a plasmonic crystal on the active area. By simulations the grating is designed to maximize transmittance variation due the plasmon resonance shift related to the surface binding of bio-analyte molecules. This event is transduced into an electrical signal at device terminals, as confirmed by characterizations on the first prototypes fabricated. The metallic grating simultaneously works as plasmonic structure and as electronic gate of the transistor in a fully integrated architecture.
SOMMARIO In questa tesi viene trattata la tematica del controllo dell’assorbimento di luce in dispositivi a semiconduttore tramite le risonanze plasmoniche proprie di nanostrutture metalliche integrate con disposizione periodica. Reticoli metallici supportano eccitazioni plasmoniche propaganti (SPP) e localizzate (LSP) e fenomeni correlati ai plasmoni di superficie, quali la trasmissione ottica straordinaria (EOT) e la creazione band gap plasmoniche, così come effetti di diffrazione convenzionali. Tali risonanze ottiche sono state combinate per regolare l’accoppiamento e la distribuzione dei fotoni incidenti in substrati semiconduttori assorbenti. In particolare consideriamo l’applicazione di tali concetti a due tipologie di dispositivi optoelettronici: celle solari fotovoltaiche e foto-transistor. Nel caso dei dispositivi fotovoltaici, l’obiettivo è aumentare l’efficienza di conversione energetica tramite una maggiore raccolta di luce e la redistribuzione del profilo di assorbimento, in modo da migliorare la raccolta dei portatori di carica fotogenerati. L’analisi di un caso di studio, un reticolo lamellare monodimensionale posto su un substrato di silicio, tramite simulazioni ottiche per via numerica, serve a trovare le condizioni di accoppiamento delle risonanze supportate, dimensionando i parametri geometrici delle nanostrutture, e mostrare il loro impatto sul profilo di generazione. Questi risultati sono quindi applicati, per finalità di “light trapping”, a due strutture realistiche di celle solari. Le risonanze SPP e LSP sono capaci di fornire una grande intensificazione del campo vicino e aumentano efficacemente l’assorbimento di celle solari organiche ultra-sottili. D’altro canto, la combinazione di EOT e ordini di diffrazione è più adatta per celle solari spesse in Si. Quindi presentiamo il processo di fabbricazione sviluppato per realizzare le nanostrutture progettate sulle ampie superfici dei dispositivi fotovoltaici in Si. Esperimenti e simulazioni mostrano che è possibile ottenere un aumento dell’efficienza quantica interna rispetto ai dispositivi non nanostrutturati. Per quanto riguarda i foto-transistor, l’obiettivo è utilizzarli come biosensori compatti e scalabili tramite l’integrazione di cristalli plasmonici sull’area attiva. Il reticolo è stato progettato in modo da massimizzare variazioni di trasmittanza dovute alla modulazione delle risonanze plasmoniche indotta dal legame di bio-molecole sulla superficie. Questo evento è trasdotto in un segnale elettrico misurabile ai capi del dispositivo, come confermato dalle caratterizzazioni sui primi prototipi fabbricati. Il reticolo metallico funziona simultaneamente come struttura plasmonica e come gate elettronico del transistor in un’architettura totalmente integrata.
XXV Ciclo
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Giannopoulos, Mihail. "Tunable bandwidth quantum well infrared photo detector (TB-QWIP)." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FGiannopoulos.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003.Thesis advisor(s): Gamani Karunasiri, James Luscombe. Includes bibliographical references (p. 59-61). Also available online.
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Lee, Sang Il. "Development of optically controlled microwave devices and artificial materials /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/6037.
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Fletcher, Robert Brian. "Engineering of optoelectronic devices based on conjugated polymers." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312804.
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Nyberg, Tobias. "Nano and micro patterned organic devices : from neural interfaces to optoelectronic devices /." Linköping : Univ, 2002. http://www.bibl.liu.se/liupubl/disp/disp2002/tek750s.pdf.
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Kerstetter, Paul Charles. "Models of optoelectronic devices suitable for electrical circuit simulation." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15807.
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Loeser, Martin. "Theory and design of broadband active optoelectronic devices /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18070.
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Mauser, Nina. "Antenna-enhanced optoelectronic probing of carbon nanotube devices." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-176237.
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A variety of electronic and optoelectronic devices based on carbon nanotubes (CNTs) has
been implemented during the last two decades. For their optoelectronic characterization,
diffraction-limited techniques such as photocurrent (PC) and electroluminescence (EL)
microscopy were employed. However, for the full characterization of these nano-devices,
novel techniques providing nanoscale spatial resolution are desired. This work presents
antenna-enhanced optoelectronic probing as a new scanning probe technique for the investigation
of nanoelectronic devices. Based on tip-enhanced near-field optical microscopy,
sub-diffraction spatial resolution is achieved by employing an optical antenna for the focusing
of light. It is applied to study PC and EL signals with a spatial resolution better than
40 nm for the first time. Complemented with antenna-enhanced Raman and topography
images, new insights into the optoelectronic properties of CNT based devices are gained.
In the first part of this thesis, an antenna-enhanced photocurrent microscopy study is
demonstrated. The signal enhancement mechanism of PC signals is investigated and
compared with expectations based on theory. While in spectroscopic applications both
the excitation AND the emission rate is enhanced, in optoelectronic applications either
the excitation OR the emission rate is affected by the antenna. Theory predicts therefore
a weaker total signal enhancement and a lower spatial resolution of optoelectronic signals
compared to Raman scattering by a factor of √2, which is experimentally confirmed.
Then, two applications are presented. First, CNT-metal interfaces are studied and an
exponential decay of the band bending at the contacts with a decay length of about
500 nm is revealed. Second, sub-diffraction potential modulations along the CNT channel
of another device are probed that remain undetected using confocal microscopy. Combined
with high-resolution spectroscopic images of the Raman signal, defects can be excluded as
the cause for these modulations. Correlating the PC with the topographic profile reveals
charges associated with a particle on the sample substrate as the possible origin.
In the second part, antenna-enhanced electroluminescence microscopy is introduced. The
EL emitted by a heterogeneous CNT network is studied with a resolution better than
40 nm. For the first time, pinning of the EL emission to a point-like region of smaller than
20 nm is observed. This strong localization occurs at a junction of at least one metallic
and one semiconducting CNT. By probing the PC signal at this junction, the presence
of a strong local electric field is revealed, probably caused by a Schottky contact. This
allows to identify impact excitation as the most likely origin of the EL emission. A second
device, based on a single CNT, was investigated and, in contrast to the network device,
the size of the EL source is extended over a length of more than 100 nm.
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Jones, Gareth Francis. "Modification of graphene for applications in optoelectronic devices." Thesis, University of Exeter, 2017. http://hdl.handle.net/10871/31537.
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In this thesis, we investigate how the optical and electronic properties of graphene may be modified in proximity to various other materials. We present several examples of how modification in this way can help make graphene better suited for specific device applications. We develop a method of up-scaling the fabrication of FeCl3-intercalated few-layer graphene from micron-sized flakes to macroscopic films so that it may be used as a transparent electrode in flexible light-emitting devices. We also find that photo-responsive junctions can be arbitrarily written into FeCl3-intercalated few-layer graphene by means of optical lithography. These junctions produce photocurrent signals that are directly proportional to incident optical power over an extended range compared to other graphene photodetectors. Through theoretical analysis of these junctions, we conclude that the enhanced cooling of hot carriers with lattice phonons is responsible for this behaviour. Finally, we trial rubrene single crystals as the light-absorbing layer in a graphene phototransistor. We find that rubrene single crystal-graphene interfaces exhibit enhanced charge transfer efficiencies under illumination with extremely weak light signals. Through a comparative study with similar devices, we conclude that the wide variation in sensitivity amongst graphene phototransistors is largely due to extraneous factors relating to device geometry and measurement conditions.
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Kinner, Lukas [Verfasser]. "Flexible transparent electrodes for optoelectronic devices / Lukas Kinner." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1228333432/34.
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Kotadiya, Naresh [Verfasser]. "Ohmic contacts for organic optoelectronic devices / Naresh Kotadiya." Karlsruhe : KIT-Bibliothek, 2021. http://d-nb.info/122745113X/34.
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Yim, Keng Hoong. "Controlling organic-organic interfaces for efficient optoelectronic devices." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612134.
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Cariello, Michele. "Synthesis of novel organic semiconductors for optoelectronic devices." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7805/.
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This thesis describes the synthesis and characterisation of novel conjugated organic materials with optoelectronic application. The first chapter provides an introduction about organic semiconductors and in particular about their working principle from a physical and chemical point of view. An overview of the most common types of solar cells is provided, including examples of some of the best performing materials. The second chapter describes the synthesis of a new library of flavin derivatives as potential active materials for optoelectronic applications. Flavins are natural redox-active molecules, which show potential application in optoelectronics, thanks to their stability and versatility. FPF-Flavins, for instance, could be used either as acceptor units in push-pull polyconjugated systems or as acceptor unit in dyes for DSSCs. In the same chapter a first attempt of synthesising bis-flavins to be used as N-type semiconductors in BHJ devices is described. The third chapter describes the successful synthesis and characterization of a series of conjugated organic molecules based on the benzothiadiazole moiety. Among these, three molecules containing ferrocene as donor unit were tested as sensitizers for DSSCs, reporting a PCE of 0.3% as the best result. Further studies indicated a significant problem of charge recombination which limits the performance. A near-infrared absorbing push-pull polymer, based on BbT as acceptor unit, was also synthesised and tested in BHJ devices as P-type semiconductor in blend with PC71BM, showing a VOC of 0.71 V. Finally, the last chapter describes the synthesis of several tetrathiafulvalene derivatives in order to explore this moiety as donor unit in dyes for DSSCs and as HTM for perovskite-based solar cells. In particular, two very simple dyes were synthesised and implemented in DSSCs reporting a PCE 0.2% and 0.4%, respectively. The low efficiency was associated to the tendency to aggregate at the solid state, with the absorption shifting from the visible to the infrared range. A conjugated molecule, containing a DPP core, was also synthesised and tested as HTM for perovskite solar cells. The best reported PCE of 7.7% was obtained without any additives. A case study about dehalogenation and “halogen dance” in TTF iodide is also presented.
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Akyol, Fatih. "Nanoscale Electron Transport Engineering for GaN Optoelectronic Devices." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462897011.
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SCHUTZMANN, STEFANO. "Towards hybrid sol-gel devices for optoelectronic biosensors." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2006. http://hdl.handle.net/2108/202687.
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I sensori per la rilevazione di sostanze inquinanti in acqua, terra e atmosfera così come i dispositivi biosensori per l’identificazione di proteine ed enzimi, rappresentano un interessantissimo ambito di ricerca con forti applicazioni in campo industriale. In questo contesto, una promettente possibilità è rappresentata dallo sviluppo di sensori basati sull’optoelettronica dato che essi assicurano un’alta sensibilità, una buona stabilità meccanica, la possibilità di miniaturizzare i dispositivi e di produrli su larga scala. In particolare, negli ultimi anni molti sforzi sono stati orientati allo sviluppo di sensori ottici a guida d’onda. Il principio di funzionamento di questo tipo di dispositivi è basato sull’interazione fra la componente del campo evanescente di un’onda guidata e la regione che si vuole analizzare.
Lo sviluppo di dispositivi optoelettronici, d’altra parte, richiede la possibilità di sintetizzare materiali dalle qualità ottiche appropriate. In particolare, la possibilità di cambiare opportunamente l’indice di rifrazione rappresenta un aspetto fondamentale per la fabbricazione di dispositivi reali. I materiali ibridi organico-inorganici sintetizzati con la tecnologia sol-gel rappresentano una valida alternativa ai più tradizionali metodi per la fabbricazione di dispositivi ottici integrati come la tecnica dello scambio ionico o la CVD (chemical vapor deposition). Questa tecnica ibrida permette lo sviluppo di materiali dalle caratteristiche nuove in modo semplice ed economico.
La presente tesi tratta dello sviluppo, della sintesi e della caratterizzazione di guide d’onda sol-gel ibride per possibili applicazioni come sensori ottici a guida d’onda.
La caratterizzazione ottica dei dispositivi è stata effettuata principalmente utilizzando un apparato sperimentale sviluppato ed ottimizzato dal candidato durante il primo periodo del lavori di dottorato. Il setup si basa sia sulla tecnica m-line sia sulla tecnica dell’angolo di Brewster e rappresenta uno strumento semplice e a basso costo per l’analisi dell’indice di rifrazione di film sottili. I risultati mostrano che l’apparato permette la stima dell’indice di rifrazione a diverse lunghezze d’onda nel visibile e nel vicino infrarosso di film aventi spessore da poche decine di nanometri a diversi micron. L’errore nella determinazione dell’indice di rifrazione è compreso nel range ±0.001-0.003 a seconda della lunghezza d’onda e delle proprietà del campione. L’ottima accuratezza e affidabilità del nostro apparato è anche confermata dal confronto con i risultati ottenuti da misure di ellissometria spettroscopica.
Molti sforzi sono stati indirizzati alla sintesi e caratterizzazione di diverse guide d’onda sol-gel deposte su substrati sia di vetro che di silicio. I campioni sono stati caratterizzati mediante misure di indice di rifrazione di perdite ottiche usando la tecnica dell’analisi della luce di scattering. I risultati hanno mostrato la possibilità di modulare l’indice di rifrazione fra 1.45 e 1.90 semplicemente modificando la sintesi chimica e i trattamenti post-deposizione. Perdite di propagazione dell’ordine di 3-10 dB/cm sono state misurate sui nostri campioni a seconda della lunghezza d’onda, della polarizzazione del modo selezionato. Questi valori sono piuttosto comuni per guide d’onda planari di tipo sol gel ibrido.
Durante questo lavoro sono state inoltre sintetizzate a caratterizzate guide d’onda drogate con molecole luminescenti al fine di mostrare la possibilità di usare le nostre strutture guidanti come dispositivi attivi. Si è investigata anche l’opportunità di modulare l’indice di rifrazione di film ibridi utilizzando le proprietà di molecole fotosensibili esposte a luce ultravioletta.
Infine, l’ultimo periodo di tesi è stato dedicato con successo ad investigare la possibilità di utilizzare la guide d’onda sol-gel ibride come strutture-base per lo sviluppo di sensori ottici a fluorescenza. A tal fine sono state condotte misure di fluorescenza eccitata mediante onda evanescente.Environment sensors for the detection of polluting substances in water, earth and atmosphere as well as biosensor devices for the recognition of proteins and enzymes represent a very intriguing topic for both research and industrial applications. In this framework, a very promising alternative is represented by the development of sensors based on optoelectronic technology since they combine high sensitivity, mechanical stability, miniaturization and the possibility of mass-production. In particular, extensive research have been devoted to evanescent-field-based optical waveguide sensors. The operation principle of this kind of devices is based on the interaction between the evanescent field component of a guided optical wave and the monitoring region. The development of optoelectronic devices requires the possibility to design materials with suitable optical properties. In particular, the possibility of changing appropriately the refractive index represents a fundamental step for design and fabrication of real devices. Hybrid organic-inorganic materials synthesized by sol-gel technology seem to be a valid alternative to more traditional methods such as ion exchange or chemical vapor deposition for fabrication of integrated optical devices. Hybrid materials combining organic and inorganic networks allow the design and fabrication of new materials with appropriate features in a simple and economic way. This thesis reported on the design, synthesis and characterization of hybrid sol-gel-based waveguides for possible applications as fluorescence-based optical sensors. Optical characterization has been accomplished using a home-made experimental setup built and optimized by the candidate during the first period of the PhD fellowship. The setup is based on both m-line and Brewster methods and represents a completely non-destructive, low cost and very simple tool for thin film refractive index estimation. Results have shown that the apparatus allows the estimation of refractive index at different wavelengths in the visible and near infrared spectral region for films having thickness from few tens of nanometers to several micrometers. The error in refractive index determination was in the range ±0.001-0.003, depending on wavelength and sample features. Comparison with results obtained by ellipsometric measurements have confirmed the high accuracy and reliability of our setup. Many efforts was dedicated to the synthesis and characterization of different hybrid sol-gel waveguides grown both on silicon and glass substrates. Samples were characterized by refractive index determination and propagation loss measurements using scattered light detection technique. Results have shown the possibility to modulate quite easily the refractive index from 1.45 to about 1.90 playing on the chemical synthesis and on the post-deposition treatments. Propagation loss coefficients in the range 3-10 dB/cm were commonly obtained on our samples, depending on wavelengths, polarization, and mode selected. These values are quite common for planar organic/inorganic sol-gel based waveguides. Waveguides doped with fluorescent molecules were synthesized and characterized showing the possibility to use our structures as active optical devices. The modulation of refractive index of hybrid films using photosensitive molecules was investigated exposing films to different UV light dose. Moreover, first efforts to fabricate channel waveguides exploiting photolithographic techniques were accomplished. Finally, the possibility to use hybrid sol-gel planar waveguides as building blocks for a fluorescence-based optical sensor has been demonstrated performing measurements of fluorescence excited by guided wave evanescent field.
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