3,615 research outputs found

    X-ray photoelectron spectroscopy investigation of nanoporous NiO electrodes sensitized with Erythrosine B

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    Nanoporous NiO thin films were prepared onto FTO glass substrates by means of screen-printing and were sensitized with Erythrosine B (EryB) dye. The obtained material was electrochemically treated and characterized with ex-situ X-ray photoelectron spectroscopy in order to gain information beneficial to the application of sensitized NiO as photocathodes of p-type dye-sensitized solar cells (p-DSCs). In particular, EryB-sensitized NiO films underwent a series of electrochemical treatments in LiClO4/Acetonitrile (ACN) electrolyte devised so as to simulate possible conditions the electrode might encounter during operation in the photoelectrochemical cell. Upon potential-cycling in a range where the two NiO faradic events Ni(II)→Ni(III) and Ni(III)→Ni(IV) occur, X-ray photoelectron spectroscopy revealed that Erythrosine B dye experiences a partial detachment from the NiO surface. This detachment seems to be paralleled by the formation of stable (Ni)+(ClO4)- couples. Overall, the EryB dye displayed an acceptable electrochemical stability onto the surface of NiO electrode up to 50 cyclic voltammetries in the range -0.27÷+1.13V vs. Ag/AgCl. These results are useful for the evaluation of electrochemical stability of the dye when this is immobilized onto an electrode surface and are beneficial for a better comprehension of the degradation phenomena operating in real photoconversion device. © 2017 Elsevier B.V

    Charge separation: From the topology of molecular electronic transitions to the dye/semiconductor interfacial energetics and kinetics

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    Charge separation properties, that is the ability of a chromophore, or a chromophore/semiconductor interface, to separate charges upon light absorption, are crucial characteristics for an efficient photovoltaic device. Starting from this concept, we devote the first part of this book chapter to the topological analysis of molecular electronic transitions induced by photon capture. Such analysis can be either qualitative or quantitative, and is presented here in the framework of the reduced density matrix theory applied to single-reference, multiconfigurational excited states. The qualitative strategies are separated into density-based and wave function-based approaches, while the quantitative methods reported here for analysing the photoinduced charge transfer nature are either fragment-based, global or statistical. In the second part of this chapter we extend the analysis to dye-sensitized metal oxide surface models, discussing interfacial charge separation, energetics and electron injection kinetics from the dye excited state to the semiconductor conduction band states

    Zinc Oxide Nanostructures for Flexible and Transparent Electronics

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    As a multifunctional material, ZnO possesses remarkable and unique properties and has attracted much research interest for use in a variety of applications. Especially, it has been regarded as a leading material for flexible and transparent electronics, which is a promising emerging technology in electronics. This dissertation studies doping behavior of Ga in ZnO for transparent electrode applications and presents new approaches to ZnO nanostructures for next-generation flexible and transparent electronics. These approaches include developing techniques that enable multiple stacked ZnO nanoflowers and thermal treatment processes at high temperature. Transparent conductive oxides have been extensively studied for the use as a transparent electrode, which is one of the most fundamental and essential parts in transparent electronic devices. In this study, Ga-doped ZnO nanorods were grown on glass substrates, and the effects of Ga doping concentration on the physical properties of ZnO nanorods were investigated using various characterization tools. ZnO nanoflower is a highly preferred nanostructure for solar cells, sensors, and photodetectors due to its high surface area to volume ratio. To-date, ZnO nanoflowers have mostly been synthesized in the form of nanopowders without a substrate, and ZnO nanoflowers grown on substrates have only been single-stacks. Atmospheric pressure plasma jet treatment was used to increase the surface area to volume ratio of ZnO nanoflowers. The plasma treatment induced a significant increase in the height and density of the ZnO nanoflowers/nanorods because the plasma effectively increased the surface energy and roughness of the seed layers while barely affecting the crystal shape and phase of the ZnO nanoflowers/nanorods. Flexible and transparent mica substrates were used for the growth of vertically well-aligned ZnO nanorods. The adoption of mica as a substrate material permitted high temperature annealing processes, which improved the structural and optical properties of ZnO nanorods with uniform surface coverage and excellent adhesion. A practical application for the synthesized ZnO nanorods is also presented in this dissertation. ZnO nanorod-based flexible and transparent dye-sensitized solar cells (DSSCs) and piezoelectric nanogenerators (NGs) were fabricated and the device performances were investigated. Although only two kinds of energy-harvesting devices (DSSCs and NGs) are presented as examples of applications in this dissertation, it is expected that this new approach will provide a breakthrough for overcoming the limited process temperature on plastic and cellulose nanopaper substrates because mica can be extensively used as a flexible and transparent substrate material for electronics, optoelectronics, energy/environmental, and biomedical applications where high temperature processes are required

    Nanotube film-enhanced 3-D photoanode for application in microsystems technology

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    Surface area plays an important factor in the energy conversion performance of solar cells. It has also emerged as a critical factor in the evolution of high-performance micro-electro-mechanical systems (MEMS) and multifunctional microstructures most of which will benefit from integrated on-chip solar power. Presented here is the hierarchical fabrication and characterization of TiO2 nanotubes on non-planar 3-dimensional microstructures for enhanced performance of the photoanode in dye-sensitized solar cells (DSSCs). The objective is to increase photoanode performance within a 1 cm2 lateral footprint area by increasing the vertical surface area through the formation of TiO2 nanotubes on 3-D microstructures. In the interest of the seamless integration of DSSCs into MEMS applications, bulk micromachining using wet-etching was employed to fabricate 3-D microstructures in silicon. Anodization was used to form titania nanotubes within sputtered titanium thin films. Film quality, adhesion, and the formation of the nanotubes are discussed. Nanotubes with approximate outer diameter dimensions of 180 nm, inner diameter of 75 nm, and heights of 340 nm on 15 um-sq x 15 um-deep micro-wells were fabricated resulting in more than 5 times the increase in surface area over planar surfaces. Grazing incidence diffraction measurements were used to negate the substrate contribution while providing a detailed in-depth profile analysis to validate the preferred polycrystalline rutile and anatase orientation on the 3D surface-texture photoanode. The increase in surface area resulted in an equal increase in dye adsorption capacity and a 78% reduction in spectral reflectance. The optical enhancement of this hierarchically-structured nanotube film-enhanced (NFE) 3D photoanode correlated well to a high current density increase 10 times that of its flat counterpart. Fabrication of a DSSC utilizing the NFE 3D photoanode was also performed and tested for its photocurrent performance under solar simulation. Results suggest that although the surface-textured anode increases the performance of the photoanode, efficiency of the overall cell significantly depends on the architecture. A conceptual implementation of the NFE 3-D photoanode into microsystems is also discussed along with conclusions and suggestions for future work

    Optimization of charge separation in organic dye-sensitized solar cells (DSSCs) with different nanostructure films and redox mediators

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    Wydział Fizyki: Zakład Fizyki Kwantowej/Centrum NanobiomedyczneBadania będące podstawą tej pracy doktorskiej odnoszą się do zagadnienia optymalizacji skomplikowanych foto-fizykochemicznych układów jakimi są barwnikowe ogniwa słoneczne (DSSC). Wiele aspektów ich budowy jest wzięte pod uwagę: rodzaj i morfologia użytego materiału fotoanody, typ użytego barwnika, różne rodzaje modyfikacji powierzchniowych elektrody, rodzaj elektrolitu oraz jego domieszki. Procesy transportowe zachodzące w tych ogniwach w skalach czasowych od fs do s zostały przebadane przy pomocy zestawu technik badawczych, m.in.: spektroskopii laserowej (UV-VIS, IR, spektroskopia czasowo-rozdzielcza), fotolizy błyskowej, elektrochemicznej spektroskopii impedancyjnej, pomiarów krzywych prądowo-napięciowych oraz obrazowania przy pomocy mikroskopii SEM i TEM. Badania laboratoryjne zostały wsparte rozważaniami teoretycznymi, które zaowocowały stworzeniem i implementacją algorytmu optymalizującego parametry pojedynczych i tandemowych ogniw słonecznych w celu zmaksymalizowania wydajności. Wszelkie wnioski są oparte na cyklu 6 publikacji składających się na rdzeń pracy i są zaprezentowane wraz krótkim opisem działania ogniw barwnikowych oraz użytych technik badawczych.The research performed in this PhD thesis revolves around optimization of a complex photo-physicochemical systems that DSSC are. Number of aspects are taken into account: the type and morphology of the photoanode material, type of the utilized dye, various types of electrode surface treatment, type of electrolyte redox couple and additional electrolyte constituents. Kinetic processes occurring in these devices on the timescales from fs to s are probed using a set of measuring techniques including: laser spectroscopy (UV-VIS, IR, transient spectroscopy), flash photolysis, electrochemical impedance spectroscopy, current-voltage measurements together with SEM and TEM imaging. Laboratory work is supported by the theoretical considerations in the form of creation and implementation of the algorithm, which optimizes parameters of single and tandem solar cells in order to obtain the highest efficiency. All the conclusions are drawn from the set of 6 publications being the backbone of the thesis and are presented together with a short description of operating principles of DSSCs and measuring techniques.Work was partially financed from the project "Rozwój środowiskowych interdyscyplinarnych studiów doktoranckich w zakresie nanotechnologii-elektroniki i fotowoltaiki w Instytucie Fizyki Molekularnej PAN w Poznaniu i na Wydziale Fizyki UAM" UDA-POKL.04.03.00-00-015/12-00 in the frame of Human Capital Operational Program funded fromEuropean Social Fund and by National Science Centre OPUS grant no. 2012/05/B/ST3/03284 named „Badanie elementarnych procesów separacji ładunku w fotoogniwach barwnikowych metodami czasowo-rozdzielczej spektroskopii optycznej”

    Determination of charge transfer dynamics and efficiency in solar cells sensitized with carbazole, indoline and triphenylamine dyes

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    Wydział FizykiNiniejsza praca została poświęcona badaniom dynamiki procesów transferu ładunku zachodzących w ogniwach słonecznych sensybilizowanych barwnikiem (ang. Dye Sensitized Solar Cells – DSSC), zawierających wysoko wydajne barwniki karbazolowe, indolinowe i trifenylaminowe. W opublikowanych artykułach, wchodzących w skład cyklu stanowiącego przedmiot tej rozprawy, opisaliśmy, jak różnorodne modyfikacje, stosowane w celu poprawienia funkcjonowania ogniw, wpływają na ultraszybkie i szybkie procesy transferu ładunku oraz jak dynamika poszczególnych procesów związana jest z całościowym funkcjonowaniem ogniw. W celu uzyskania informacji o dynamice procesów transferu ładunku, ich wydajności oraz o powiązaniu tych cech z parametrami fotowoltaicznymi ogniw, wykorzystano szeroki zakres technik eksperymentalnych, obejmujący podstawową charakterystykę fotowoltaiczną i różnorodne metody stacjonarnej i czasowo rozdzielczej spektroskopii optycznej. Część wstępna (rozdziały 1 – 4) zawiera wprowadzenie opisujące stan wiedzy na temat układów DSSC. Praca zawiera również dokładne objaśnienie metodyki wytwarzania ogniw DSSC jak również opis najważniejszych technik wykorzystanych do ich badań. Publikacje naukowe, wchodzące w skład niniejszej pracy, podsumowane zostały w rozdziale piątym i zamieszczone za rozdziałem nr 6, gdzie podsumowano konkluzje pracy.The main concern of this thesis is the dynamics of charge transfer processes occurring in Dye Sensitized Solar Cells (DSSC) comprising a top efficient carbazole, indoline and triphenylamine dyes. This dissertation is based on a series of papers reporting the effects of different modifications applied to improve DSSCs on ultrafast and fast charge transfer processes and relation between the dynamics of particular charge transfer phenomena and the overall DSSC performance. In order to gain the information on the dynamics of charge transfer processes, their efficiency and relationship with the overall photovoltaic performance of studied devices, a broad range of experimental techniques was applied, including basic photovoltaic characterization methods, electrochemical impedance spectroscopy, and a variety of stationary and time resolved optical spectroscopy methods. The opening part of the dissertation (chapters 1 – 4) provides an introduction to the current state of knowledge on DSSC. Subsequently, main experimental methods including fabrication and key characterization techniques used for purposes of this thesis are thoroughly described. The scientific papers making the basis of this thesis are described in chapter 5 and attached after chapter 6 presenting the conclusions.I kindly acknowledge the financial support from the Polish National Science Centre under project 2015/18/E/ST4/00196

    Cobalt-Based Electrolytes for Dye-Sensitized Solar Cells: Recent Advances towards Stable Devices

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    Redox mediators based on cobalt complexes allowed dye-sensitized solar cells (DSCs) to achieve efficiencies exceeding 14%, thus challenging the emerging class of perovskite solar cells. Unfortunately, cobalt-based electrolytes demonstrate much lower long-term stability trends if compared to the traditional iodide/triiodide redox couple. In view of the large-scale commercialization of cobalt-based DSCs, the scientific community has recently proposed various approaches and materials to increase the stability of these devices, which comprise gelling agents, crosslinked polymeric matrices and mixtures of solvents (including water). This review summarizes the most significant advances recently focused towards this direction, also suggesting some intriguing way to fabricate third-generation cobalt-based photoelectrochemical devices stable over time
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