84 research outputs found

    Feature Papers in Electronic Materials Section

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    This book entitled "Feature Papers in Electronic Materials Section" is a collection of selected papers recently published on the journal Materials, focusing on the latest advances in electronic materials and devices in different fields (e.g., power- and high-frequency electronics, optoelectronic devices, detectors, etc.). In the first part of the book, many articles are dedicated to wide band gap semiconductors (e.g., SiC, GaN, Ga2O3, diamond), focusing on the current relevant materials and devices technology issues. The second part of the book is a miscellaneous of other electronics materials for various applications, including two-dimensional materials for optoelectronic and high-frequency devices. Finally, some recent advances in materials and flexible sensors for bioelectronics and medical applications are presented at the end of the book

    Characterization of alternative carrier selective materials and their application to heterojunction solar cells

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    Crystalline silicon (c-Si) solar cells can be considered a highly industrialized and mature product with a record conversion efficiency of 26.6%, not far from the practical limit of 29.4% (for single p/n junction devices). Accordingly, current research and development are addressing some remaining efficiency and cost limitations, including the reduction of (1) carrier recombination in highly doped materials, (2) parasitic absorption by narrow band gap films and (3) high temperature energy-intensive processing (especially critical for wafer thicknesses below 100 µm). In parallel, thin-film PV (e.g. organics and perovskites) have introduced a large number of dopant-free, hole- or electron-selective materials with optoelectronic properties that are comparable or superior to standard p- and n-doped layers in c-Si. Consequently, this thesis work explores novel heterojunctions between c-Si and these carrier-selective contact materials, putting special emphasis on TMO thin films whose wide energy band gap (>3 eV), surface passivation and large work function (>5 eV) characteristics permit their utilization as transparent/passivating/hole-selective front contacts in n-type c-Si (n-Si) solar cells. To this purpose, a comparative study among three thermally evaporated TMOs (V2O5, MoO3 and WO3) allowed correlating their chemical composition with thin film conductivity, optical transmittance, passivation potential and contact resistance on n-Si substrates. The variation of these properties with film thickness, air exposure or temperature annealings was also studied. Overall, V2Ox outperformed the other oxides by obtaining higher implied open-circuit voltages and lower contact resistances, translating into higher selectivities. Next, a thorough study of the TMO/c-Si interface was performed by electron microscopy, secondary ion-mass spectrometry and x-ray photoelectron spectroscopy, identifying two separate contributions to the observed passivation: (1) a chemical component, as evidenced by a thin SiOx interlayer naturally-grown by chemical reaction during TMO evaporation; and (2) a "field-effect" component, a result of a strong inversion (p+) of the n-Si surface, induced by the large work function difference between both materials. Considering all this, an energy band diagram for the TMO/SiOx/n-Si heterojunction was proposed, reflecting the possible physicochemical mechanisms behind c-Si passivation and carrier transport. Then, the characterized TMO/n-Si heterojunctions were implemented as front hole contacts in complete solar cell devices, using thin TMO films (15 nm) contacted by an indium-tin oxide (ITO) anti-reflection/conductive electrode and a silver finger grid. As rear electron contacts, n-type a-SiCx:H thin films (20 nm) were used in localized (laser-doped) and full-area configurations, the former contacted by titanium/aluminum while the latter by ITO/silver electrodes. The best performance solar cells were obtained for V2Ox/n-Si heterojunctions, characterized by an open-circuit voltage (VOC) close to 660 mV and a maximum conversion efficiency of 16.5%. Additional characterization confirmed the good quality of the induced p+/n-Si junction, with ideality factors close to 1 and built-in potentials above 700 mV. Moreover, a photocurrent gain of ~1 mA/cm2 (300-550 nm wavelength range) was directly attributed to the difference in energy band gaps between TMOs (>2.5 eV) and the a-SiCx:H reference (~1.7 eV). On a sideline, hole-selective contacts based on PEDOT:PSS polymer solutions were also characterized, resulting in a moderate conversion efficiency of 11.6% in ITO-free devices. Finally, it is worth emphasizing the high degree of innovation in this thesis project, reporting for the first time the properties of these alternative contact materials in the context of c-Si photovoltaics and contributing to a more generic understanding of solar cell operation and design.Las celdas solares de silicio cristalino (c-Si) pueden ser consideradas un producto maduro y altamente industrializado, con eficiencias de conversión record de 26.6% muy cercanas al límite práctico de 29.4%. En consecuencia, la investigación y desarrollo actuales están abordando las limitantes restantes en eficiencia y costes, incluyendo la reducción de (1) la recombinación de portadores en materiales altamente dopados, (2) la absorción parásita debido a energías de banda prohibida insuficientes y (3) los procesos térmicos (un factor crítico para obleas delgadas de 100 micras o menos). En paralelo, tecnologías de capa delgada (e.g. orgánicos y perovskitas) han introducido un gran número de materiales selectivos a electrones o huecos, libres de dopantes y cuyas propiedades optoelectrónicas son comparables o superiores a las capas dopadas tipo-n o tipo-p usadas de manera estándar en c-Si. Es así que esta tesis explora heterouniones novedosas entre c-Si y dichos materiales de contacto selectivos, poniendo especial énfasis en capas delgadas de TMOs cuya energía de band prohibida (>3 eV), pasivación superficial y alta función de trabajo (>5 eV) permiten su utilización como contactos frontales, transparentes, pasivantes y selectivos a huecos en celdas con substrato tipo-n (n-Si). Con este propósito, se realizó un estudio comparativo entre tres TMOs evaporados térmicamente (V2O5, MoO3 and WO3) que permitió correlacionar su composición química con la conductividad, transmitancia óptica, pasivación y resistencia de contacto de capas delgadas sobre sustratos de n-Si. La variabilidad de estas propiedades con el grosor de las capas, su exposición al aire o a recocidos de alta temperatura también fue estudiada. En general, V2Ox tuvo un mejor desempeño que el resto de los óxidos al obtener mayores pseudo-voltajes de circuito abierto y menores resistencias de contacto, traduciéndose en una mayor selectividad. En seguida, un estudio detallado de la interface TMO/c-Si fue llevado a cabo mediante microscopia de electrones, espectrometría de masas de iones secundarios y espectroscopia fotoelectrónica de rayos-x, identificando dos contribuciones a la pasivación superficial: (1) un componente químico, demostrado por la presencia de una inter-capa de SiOx formada mediante reacción química durante el depósito del TMO; y (2) un componente de "efecto de campo", que es resultado de la fuerte inversión de la superficie (p+/n-Si) inducida por la gran disparidad en funciones de trabajo entre ambos materiales. Bajo esta consideración, se propuso un diagrama de bandas para la heterounión TMO/SiOx/n-Si que refleja los posibles mecanismos de pasivación y transporte de cargas. Acto seguido, se implementaron dichas heterouniones como contactos tipo-p frontales en celdas solares finalizadas, con la estructura Ag/ITO(80 nm)/TMO (15 nm)/n-Si, donde el ITO "óxido de indio y estaño" sirve de capa antirreflejo conductora y la plata como electrodo. Para el contacto tipo-n trasero, capas de a-SiCx:H dopado (20 nm) fueron utilizadas en dos configuraciones (dopado puntual por láser y contacto en área completa). El mejor desempeño se obtuvo para las celdas de V2Ox/n-Si, caracterizadas por voltajes de circuito abierto (Voc) cercanos a 660 mV y una eficiencia máxima de 16.5%. La caracterización adicional de estos dispositivos reveló factores de idealidad cercanos a 1 y una barrera interna de potencial mayor a 700 mV, comprobando la buena calidad de la unión p+/n-Si inducida. Además, ganancias en fotocorriente de ~1 mA/cm2 (para el rango de longitudes de onda de 300-550 nm) fueron directamente atribuidas a las diferencias en energías de banda prohibida entre el TMO (>2.5 eV) y la capa referencia de a-SiCx:H (~1.7 eV). Finalmente, vale la pena enfatizar el alto grado de innovación en este proyecto de tesis, reportando por primera vez las propiedades de estos materiales de contacto alternativos en el contexto de la fotovoltaica de silicio

    Characterization of alternative carrier selective materials and their application to heterojunction solar cells

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    Crystalline silicon (c-Si) solar cells can be considered a highly industrialized and mature product with a record conversion efficiency of 26.6%, not far from the practical limit of 29.4% (for single p/n junction devices). Accordingly, current research and development are addressing some remaining efficiency and cost limitations, including the reduction of (1) carrier recombination in highly doped materials, (2) parasitic absorption by narrow band gap films and (3) high temperature energy-intensive processing (especially critical for wafer thicknesses below 100 µm). In parallel, thin-film PV (e.g. organics and perovskites) have introduced a large number of dopant-free, hole- or electron-selective materials with optoelectronic properties that are comparable or superior to standard p- and n-doped layers in c-Si. Consequently, this thesis work explores novel heterojunctions between c-Si and these carrier-selective contact materials, putting special emphasis on TMO thin films whose wide energy band gap (>3 eV), surface passivation and large work function (>5 eV) characteristics permit their utilization as transparent/passivating/hole-selective front contacts in n-type c-Si (n-Si) solar cells. To this purpose, a comparative study among three thermally evaporated TMOs (V2O5, MoO3 and WO3) allowed correlating their chemical composition with thin film conductivity, optical transmittance, passivation potential and contact resistance on n-Si substrates. The variation of these properties with film thickness, air exposure or temperature annealings was also studied. Overall, V2Ox outperformed the other oxides by obtaining higher implied open-circuit voltages and lower contact resistances, translating into higher selectivities. Next, a thorough study of the TMO/c-Si interface was performed by electron microscopy, secondary ion-mass spectrometry and x-ray photoelectron spectroscopy, identifying two separate contributions to the observed passivation: (1) a chemical component, as evidenced by a thin SiOx interlayer naturally-grown by chemical reaction during TMO evaporation; and (2) a "field-effect" component, a result of a strong inversion (p+) of the n-Si surface, induced by the large work function difference between both materials. Considering all this, an energy band diagram for the TMO/SiOx/n-Si heterojunction was proposed, reflecting the possible physicochemical mechanisms behind c-Si passivation and carrier transport. Then, the characterized TMO/n-Si heterojunctions were implemented as front hole contacts in complete solar cell devices, using thin TMO films (15 nm) contacted by an indium-tin oxide (ITO) anti-reflection/conductive electrode and a silver finger grid. As rear electron contacts, n-type a-SiCx:H thin films (20 nm) were used in localized (laser-doped) and full-area configurations, the former contacted by titanium/aluminum while the latter by ITO/silver electrodes. The best performance solar cells were obtained for V2Ox/n-Si heterojunctions, characterized by an open-circuit voltage (VOC) close to 660 mV and a maximum conversion efficiency of 16.5%. Additional characterization confirmed the good quality of the induced p+/n-Si junction, with ideality factors close to 1 and built-in potentials above 700 mV. Moreover, a photocurrent gain of ~1 mA/cm2 (300-550 nm wavelength range) was directly attributed to the difference in energy band gaps between TMOs (>2.5 eV) and the a-SiCx:H reference (~1.7 eV). On a sideline, hole-selective contacts based on PEDOT:PSS polymer solutions were also characterized, resulting in a moderate conversion efficiency of 11.6% in ITO-free devices. Finally, it is worth emphasizing the high degree of innovation in this thesis project, reporting for the first time the properties of these alternative contact materials in the context of c-Si photovoltaics and contributing to a more generic understanding of solar cell operation and design.Las celdas solares de silicio cristalino (c-Si) pueden ser consideradas un producto maduro y altamente industrializado, con eficiencias de conversión record de 26.6% muy cercanas al límite práctico de 29.4%. En consecuencia, la investigación y desarrollo actuales están abordando las limitantes restantes en eficiencia y costes, incluyendo la reducción de (1) la recombinación de portadores en materiales altamente dopados, (2) la absorción parásita debido a energías de banda prohibida insuficientes y (3) los procesos térmicos (un factor crítico para obleas delgadas de 100 micras o menos). En paralelo, tecnologías de capa delgada (e.g. orgánicos y perovskitas) han introducido un gran número de materiales selectivos a electrones o huecos, libres de dopantes y cuyas propiedades optoelectrónicas son comparables o superiores a las capas dopadas tipo-n o tipo-p usadas de manera estándar en c-Si. Es así que esta tesis explora heterouniones novedosas entre c-Si y dichos materiales de contacto selectivos, poniendo especial énfasis en capas delgadas de TMOs cuya energía de band prohibida (>3 eV), pasivación superficial y alta función de trabajo (>5 eV) permiten su utilización como contactos frontales, transparentes, pasivantes y selectivos a huecos en celdas con substrato tipo-n (n-Si). Con este propósito, se realizó un estudio comparativo entre tres TMOs evaporados térmicamente (V2O5, MoO3 and WO3) que permitió correlacionar su composición química con la conductividad, transmitancia óptica, pasivación y resistencia de contacto de capas delgadas sobre sustratos de n-Si. La variabilidad de estas propiedades con el grosor de las capas, su exposición al aire o a recocidos de alta temperatura también fue estudiada. En general, V2Ox tuvo un mejor desempeño que el resto de los óxidos al obtener mayores pseudo-voltajes de circuito abierto y menores resistencias de contacto, traduciéndose en una mayor selectividad. En seguida, un estudio detallado de la interface TMO/c-Si fue llevado a cabo mediante microscopia de electrones, espectrometría de masas de iones secundarios y espectroscopia fotoelectrónica de rayos-x, identificando dos contribuciones a la pasivación superficial: (1) un componente químico, demostrado por la presencia de una inter-capa de SiOx formada mediante reacción química durante el depósito del TMO; y (2) un componente de "efecto de campo", que es resultado de la fuerte inversión de la superficie (p+/n-Si) inducida por la gran disparidad en funciones de trabajo entre ambos materiales. Bajo esta consideración, se propuso un diagrama de bandas para la heterounión TMO/SiOx/n-Si que refleja los posibles mecanismos de pasivación y transporte de cargas. Acto seguido, se implementaron dichas heterouniones como contactos tipo-p frontales en celdas solares finalizadas, con la estructura Ag/ITO(80 nm)/TMO (15 nm)/n-Si, donde el ITO "óxido de indio y estaño" sirve de capa antirreflejo conductora y la plata como electrodo. Para el contacto tipo-n trasero, capas de a-SiCx:H dopado (20 nm) fueron utilizadas en dos configuraciones (dopado puntual por láser y contacto en área completa). El mejor desempeño se obtuvo para las celdas de V2Ox/n-Si, caracterizadas por voltajes de circuito abierto (Voc) cercanos a 660 mV y una eficiencia máxima de 16.5%. La caracterización adicional de estos dispositivos reveló factores de idealidad cercanos a 1 y una barrera interna de potencial mayor a 700 mV, comprobando la buena calidad de la unión p+/n-Si inducida. Además, ganancias en fotocorriente de ~1 mA/cm2 (para el rango de longitudes de onda de 300-550 nm) fueron directamente atribuidas a las diferencias en energías de banda prohibida entre el TMO (>2.5 eV) y la capa referencia de a-SiCx:H (~1.7 eV). Finalmente, vale la pena enfatizar el alto grado de innovación en este proyecto de tesis, reportando por primera vez las propiedades de estos materiales de contacto alternativos en el contexto de la fotovoltaica de silicio.Postprint (published version

    Synthesis and characterization of conducting polymer nanostructures and their application in sensors

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    A one-step synthesis technique has been used to fabricate sensors by growing polyaniline nanofibers and polyaniline/metal nanocomposites in the active area of an interdigitated electrode array. Polyaniline nanofiber sensors can be fabricated by irradiating an aqueous precursor solution containing aniline, HCl, a metal salt, and ammonium persulfate (APS) with a high pressure Hg lamp. The sensors are ready for operation after polymerization is complete, and no additional processing steps are necessary. These sensors showed faster and more intensity response to various organic vapors than conventional bulk polyaniline sensors due to their larger surface area. A chemisorption model and a diffusion model were used to fit the sensor response of nanostructured polyaniline sensors. Both models can mathematically fit the sensor response as a function of time. Fitting errors from the two models were in a reasonable range, both allowing reasonable mathematical forms for the time-dependent and concentration behavior. An oligomer-assisted polymerization method was carried out to synthesize polythiophene nanofibers. In this approach, a solution of thiophene, FeCl₃, and terthiophene was dissolved in acetonitrile. Compared to conventional chemical polymerization, a polythiophene oligomer, terthiophene or bithiophene, was added to assist the formation of nanofibers. The polythiophene collected after the 12 h reaction time was found to have nanofibrilar morphology with an average diameter of about 40-50 nm. Unlike other hard-template or soft-template techniques, this method does not require the introduction of a heterogeneous phase --Abstract, page iv

    Annual report / IFW, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden

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    Towards Oxide Electronics:a Roadmap

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    At the end of a rush lasting over half a century, in which CMOS technology has been experiencing a constant and breathtaking increase of device speed and density, Moore's law is approaching the insurmountable barrier given by the ultimate atomic nature of matter. A major challenge for 21st century scientists is finding novel strategies, concepts and materials for replacing silicon-based CMOS semiconductor technologies and guaranteeing a continued and steady technological progress in next decades. Among the materials classes candidate to contribute to this momentous challenge, oxide films and heterostructures are a particularly appealing hunting ground. The vastity, intended in pure chemical terms, of this class of compounds, the complexity of their correlated behaviour, and the wealth of functional properties they display, has already made these systems the subject of choice, worldwide, of a strongly networked, dynamic and interdisciplinary research community. Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics

    Annual report / IFW, Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden

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    Functional oxides for optoelectronics

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    Il riscaldamento globale è tra le problematiche più urgenti che dobbiamo affrontare. Diminuire il consumo energetico e incrementare l’energia prodotta da fonti rinnovabili piuttosto che dai combustibili fossili sono azioni fondamentali per affrontare il cambiamento climatico. Dato che l’illuminazione è responsabile del 20% del consumo totale di energia e che il fotovoltaico è tra le fonti di energia rinnovabile che è cresciuta di più negli ultimi decenni, l’optoelettronica riveste un ruolo centrale in questa sfida. Molti degli impressionanti miglioramenti raggiunti negli ultimi decenni in questo campo sono stati resi possibili dallo sviluppo e dall’ottimizzazione dei materiali impiegati. Film sottili e nanostrutture di ossidi sono stati studiati in questo lavoro come una possibile soluzione a problematiche nel settore dell’optoelettronica. In particolare, nanocristalli di CsPbBr3 sono di largo interesse come emettitori di luce, ma risultano poco stabili quando esposti a umidità, solventi polari, ecc. Di conseguenza, nanocristalli di CsPbBr3 sono stati incapsulati in un guscio di silica (CsPbBr3@SiO2) sfruttando una reazione tra l’anidride maleica e il legante oleilammina sulla superficie del CsPbBr3. In particolare, nanocristalli di Cs4PbBr6 vengono convertiti dall’anidride maleica in nanocristalli di CsPbBr3 e l’aggiunta di un precursore della silica permette l’incapsulamento. Ulteriori esperimenti hanno rivelato il ruolo cruciale dei nanocristalli di Cs4PbBr6 e dell’ambiente di reazione ottenuto dopo la loro conversione per garantire la formazione di CsPbBr3@SiO2. Questo lavoro apre la strada allo studio della reattività dei leganti superficiali per l’incapsulazione dei nanocristalli, ma anche per strade alternative per lo scambio o la rimozione dei liganti, una nuova chimica per nanomateriali più stabili. Gli ossidi funzionali sono stati investigati anche in forma di film sottili per applicazioni fotovoltaiche. In dettaglio, la commercializzazione di celle solari a base di materiali emergenti come Cu(In,Ga)Se2 e Sb2Se3 contengono un buffer layer a base di CdS, un composto altamente tossico che ostacola la loro commercializzazione. Zn(1-x)MgxO è stato identificato come un potenziale materiale alternativo per celle solari a base di Cu(In,Ga)Se2 mentre la titania per Sb2Se3. Film sottili di Zn(1-x)MgxO sono stati preparati mediante deposizione da bagno chimico su substrati di vetro. E’ stato studiato il ruolo dell’etanolammina e dell’acido citrico insieme al contenuto di Mg sulle proprietà del film con lo scopo di impiegare questi film come buffer layer in celle solari al Cu(In,Ga)Se2 anche mediate calcoli degli equilibri in soluzione per comprendere il meccanismo di formazione del film. Analogamente, film sottili di titania sono stati preparati mediante spin coating su ossido di stagno drogato fluoro. Un trattamento acido è stato investigato per controllare il drogaggio nel film sottile di titania al fine di ottimizzare le performance della cella solare. Alcuni calcoli termodinamici sono stati eseguiti per confrontare la stabilità di fasi a diverso contenuto di titanio e di ossigeno.Nowadays, global warming is among the most urgent challenges that we have to meet. Decrease the energy consumption and enhance the amount of energy produced trough renewable sources rather than fossil fuels are imperative actions to deal with climate change. Since lighting is responsible of about 20 % of the total energy consumption and since photovoltaics is among the renewable energy source that grew more in the last decades, optoelectronics is a central field in such a challenge. Many of the crucial improvements that have been reached in the last decades in this field were made possible thanks to the development and optimization of the materials involved. In this study, oxides were investigated at the nanoscale and in the form of thin films as valuable solutions to current issues in modern optoelectronics. In particular, CsPbBr3 nanocrystals are interesting materials for light emission applications, but they suffer from poor stability against moisture, polar solvents etc. As a consequence, the reaction between maleic anhydride and the oleylamine capping ligand was exploited to encapsulate CsPbBr3 nanocrystals in SiO2 shells (CsPbBr3@SiO2). Maleic anhydride converted the starting Cs4PbBr6 nanocrystals into CsPbBr3 ones, and the addition of silica precursor promoted the shell growth. Further experiments revealed the crucial role played by Cs4PbBr6 nanocrystals as a starting material and of the reaction environment in order to successfully grow CsPbBr3@SiO2. This study paves the way for the exploitation of the reactivity of surface capping ligands for the encapsulation of nanocrystals, and potentially also for ligand exchange or stripping, a new chemistry route for more stable nanomaterials. Functional oxides were also investigated in the form of thin films for solar cell applications. Cu(In,Ga)Se2 and Sb2Se3 are emerging photovoltaic technologies whose market availability is limited by the presence of a toxic CdS buffer layer. Zn(1-x)MgxO was identified as a potential alternative oxide for the deposition of buffer layers for Cu(In,Ga)Se2 solar cells, whereas titania was investigated for cells based on Sb2Se3. In view of their application as buffer layers in Cu(In,Ga)Se2 solar cells, Zn(1-x)MgxO thin films were grown trough chemical bath deposition onto soda lime glass, in order to optimize the extent of Mg incorporation and the morphology of the film, the role of the complexing agent citric acid together with the nominal Mg amount was investigated. Likewise, titania thin films were prepared trough spin coating onto fluorine-doped thin oxide substrates. Several attempts were devoted to control and measure the n-type doping of the titania layers trough an acidic treatment with the final goal of improving the solar cell performance. Lastly, thermodynamic calculations allowed a stability comparison among TixOy species

    Micro/nanopatterned superhydrophobic surfaces fabrication for biomolecules and biomaterials manipulation and analysis

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    Superhydrophobic surfaces display an extraordinary repulsion to water and water-based solutions. This effect emerges from the interplay of intrinsic hydrophobicity of the surface and its morphology. These surfaces have been established for a long time and have been studied for decades. The increasing interest in recent years has been focused towards applications in many different fields and, in particular, biomedical applications. In this paper, we review the progress achieved in the last years in the fabrication of regularly patterned superhydrophobic surfaces in many different materials and their exploitation for the manipulation and characterization of biomaterial, with particular emphasis on the issues affecting the yields of the fabrication processes and the quality of the manufactured devices

    VISUALISING THE VERTICAL ENERGETIC LANDSCAPE IN ORGANIC PHOTOVOLTAICS

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    The aim of this thesis is to achieve a better understanding of the energetic alignment in organic multi-layered devices. The first part of this thesis is dedicated to the investigation of a new class of non-fullerene acceptor materials, N-Heteroacenes, in organic solar cells. Intentionally varying the side chain structure enables a threefold increase in device performance, partly due to an improved active layer morphology. In addition, by employing transient absorption spectroscopy, an uncommon electric field-dependent charge separation is found, starkly different than for the case of conventional fullerene acceptors. In the second part of this thesis, a novel method for the investigation of energy level alignment in organic layers is developed, based on combining ultra-violet photoemission spectroscopy and essentially damage-free argon gas cluster etching. The efficacy of the technique is shown on several state-of-the-art high-performance photovoltaic systems, with estimated photovoltaic gaps being in excellent agreement with charge transfer state energies, and in direct correlation with corresponding open-circuit voltages. Furthermore, the versatility of the technique is exemplified by its application to study the evolution of the energetic alignment upon environmental degradation, vertical stratification, injection barriers at buried interfaces, side-chain variation, molecular doping and the energetic alignment in ternary blend systems. This work demonstrates the potential and wide applicability of our novel technique for understanding the vertical composition and energetic alignment in organic thin films. This understanding is crucial towards the future development of optoelectronic organic devices
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