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Transparent Conducting Oxides (TCOs) exhibit a large and ultrafast intensity-dependent refractive index in their Epsilon-Near-Zero (ENZ) spectral region, which depends dramatically on the material properties and measurement arrangement conditions. Therefore, attempts to optimize the nonlinear response of ENZ TCOs usually involve extensive nonlinear optical measurements. In this work, we show that significant experimental work can be avoided by carrying out an analysis of the material’s linear optical response. The analysis accounts for the impact of thickness-dependent material parameters on the absorption and field intensity enhancement under different measurement conditions and estimates the incidence angle required for achieving the maximum nonlinear response for a given TCO film. We perform measurements of angle-dependent and intensity-dependent nonlinear transmittance for Indium-Zirconium Oxide (IZrO) thin films with different thicknesses and demonstrate a good agreement between the experiment and theory. Our results also indicate that the film thickness and the excitation angle of incidence can be adjusted simultaneously to optimize the nonlinear optical response, allowing a flexible design of TCO-based highly nonlinear optical devices.

Collimating and concentrating broad-band diffused light can increase the yield, decrease the cost, and open new opportunities for solar-generated electricity. Adherence to the second law of thermodynamics requires that collimation, and therefore the reduction of étendue or entropy, of diffused sunlight, i.e., light scattered by clouds or the atmosphere, can only occur if the photons lose energy during the process. This principle has been demonstrated in luminescent solar concentrators; solar photons are energetically down-shifted by a luminophore and the emitted photons are trapped within a transparent matrix and guided toward an edge lining solar cell. However, this process suffers from low efficiency as the photons are trapped within the waveguide for a long time, encountering many instances of accumulating loss mechanisms. Here, we theoretically describe and experimentally demonstrate the first free-space diffused light collimation system which overcomes these efficiency losses. The high photon energy solar spectrum is allowed to enter the system from all angles, whereas the re-emitted luminescent photons can only escape under a desired emission cone. We achieved this through doping a polymethylmetacrylate waveguide with Lumogen Red dye, which we cover on one side with a Lambertian reflector for photon recycling and induced randomization and on the top face with a complex multilayer dielectric nanophotonic coating stack. We experimentally found an angular concentration of 118% within the designed escape cone, where isotropic emission corresponds to 100%, thereby verifying the reduction of étendue in free space experimentally. Such free-space collimation systems will enable efficient redirection of sunlight toward solar panels, thereby increasing yield, decreasing heating through the emission of low energy photons, and expanding the range of available surfaces from which sunlight can be harvested.

0.67[Pb(Mg1/3Nb2/3)O3]-0.33[PbTiO3] (PMN-33PT) epitaxial thin films were prepared by pulsed-laser deposition (PLD) using ceramic targets, enriched with PbO (and MgO). The phase composition and crystal structure were analyzed by high-resolution X-ray diffraction. Accurate chemical analysis of the thin films was carried out using wavelength-dispersive X-ray spectroscopy, which revealed that the target-substrate material transfer is not fully stoichiometric. The largest deviations were found for Pb and Mg content. Our results show that it is possible to effectively tune the stoichiometry of the films via the use of custom-made ceramic targets, emphasizing their advantage over single-crystal targets in PLD growth of complex metal oxides. The functional response of the films, however, is the result of complex interactions between the crystal structure, microstructure and chemical composition of the films. Our results show that the sample, prepared from the target with 20 mol% PbO excess, with the largest deviations from the nominal stoichiometry, exhibits the highest longitudinal piezoelectric coefficient.

The relatively large ionic radius of the Na ion is one of the primary reasons for the slow diffusion of Na ions compared to that of Li ions in de/intercalation processes in sodium-ion batteries (SIBs). Interlayer expansion of intercalation hosts is one of the effective techniques for facilitating Na-ion diffusion. For most ionic layered compounds, interlayer expansion relies on intercalation of guest ions. It is important to investigate the role of these ions for material development of SIBs. In this study, alkali-metal ions (Li+, Na+, K+, and Cs+) with different sizes were intercalated into lepidocrocite-type layered titanate by a simple ion-exchange technique to achieve interlayer modulation and those were then evaluated as anode materials for SIBs. By controlling the intercalated alkaline ion species, basal spacings of layered titanates (LTs) in the range of 0.68 to 0.85 nm were obtained. Interestingly, the largest interlayer spacing induced by the large size of Cs did not yield the best performance, while the Na intercalated layered titanate (Na-ILT) demonstrated a superior performance with a specific capacity of 153 mAh g-1 at a current density of 0.1 A g-1. We found that the phenomena can be explained by the high alkaline metal ion concentration and the efficient utilization of the active sites in Na-ILT. The detailed analysis indicates that large intercalating ions like Cs can hamper sodium-ion diffusion although the interlayer spacing is large. Our work suggests that adopting an appropriate interlayer ion species is key to developing highly efficient layered electrode materials for SIBs.

We present how mesoporosity can be engineered in transition metal phosphate (TMPs) materials in a template-free manner. The method involves a transformation of a precursor metal phosphate phase, M-struvite (NH4MPO4·6H2O, M = Mg2+, Ni2+, Co2+, Nix2+Co1-x2+), and it relies on the thermal decomposition of crystalline M-struvite precursors to an amorphous and simultaneously mesoporous phase which forms while degassing of NH3 and H2O from crystals. The temporal evolution of mesoporous frameworks and the response of the coordination metal coordination environment were followed with in-situ and ex-situ scattering and diffraction, as well as X -ray spectroscopy. We highlight the systematic differences in absolute surface area, pore shape, pore size, and phase transitions depending on a metal cation present in the analogous M-struvites. In a complex amorphous structure, thermally decomposed Mg-, Ni- and NixCo1-x-struvites exhibit high surface areas and pore volumes (240 m²g-1 and 0.32 cm-3 g-1 for Mg and 90 m²g-1 and 0.13 cm-3 g-1 for Ni) for phosphate materials with a spherical to channel-like pore geometry. Despite sharing the same precursor struvite structure, different amorphous and mesoporous structures were obtained in the chemical systems. We propose that the low-cost, environmentally friendly M-struvites could be obtained as recycling products from industrial and agricultural wastewaters. These waste products could be then upcycled into mesoporous TMPs through a simple thermal treatment for further applications in (electro)catalysis.

Vanadium dioxide (VO2) is a popular candidate for electronic and optical switching applications due to its well-known semiconductor-metal transition. Its study is notoriously challenging due to the interplay of long and short range elastic distortions, as well as the symmetry change, and the electronic structure changes. The inherent coupling of lattice and electronic degrees of freedom opens the avenue towards mechanical actuation of single domains. In this work, we show that we can manipulate and monitor the reversible semiconductor-to-metal transition of VO2 while applying a controlled amount of mechanical pressure by a nanosized metallic probe using an atomic force microscope. At a critical pressure, we can reversibly actuate the phase transition with a large modulation of the conductivity. Direct tunneling through the VO2-metal contact is observed as the main charge carrier injection mechanism before and after the phase transition of VO2. The tunneling barrier is formed by a very thin but persistently insulating surfacelayer of the VO2. The necessary pressure to induce the transition decreases with temperature. In addition, we measured the phase coexistence line in a hitherto unexplored regime. Our study provides valuable information on pressure-induced electronic modifications of the VO2 properties, as well as on nanoscale metal-oxide contacts, which can help in the future design of oxide electronics., Y.A.B. and K.S. contributed equally. 30 pages, 4 figures, Supplemental Material (28 pages, 16 figures)

Fast charging performance is essential for electrode materials of batteries in portable devices as well as electric vehicles. In order to support the further development of fast charging batteries, a better understanding of the relation between the intrinsic properties and the fast charging performance is urgently required, which can be achieved by the separation of mass transfer and charge transfer limitations to the fast charging performance. However, this ability is beyond the reach of the current theoretical models. In this work, a new theoretical framework is proposed to decouple the influences of ohmic resistance, reaction rate, and ion diffusion to the fast-charging properties of electrodes. The electrode geometry and dimensions are also incorporated in the model. The new model was successfully validated by analyzing cyclic voltammetry data of 4 typical electrode materials, i.e., lithium titanate, lithium iron phosphate, titanium oxide (anatase), and niobium oxide. Surprisingly, we found that the reaction rate limits the fast charging performance in all materials that we analyzed. The extended model also allows to determine the three contributions in different reaction stages. The new model is considered to facilitate electrode design and boost the development of the next generations of fast-charging batteries.

Polymer brushes, coatings of polymers covalently end-grafted to a surface, have been proposed as a more stable alternative to traditional physisorbed coatings. However, when such coatings are applied in settings such as vapor sensing and gas separation technologies, their responsiveness to solvent vapors becomes an important consideration. It can be anticipated that the end-anchoring in polymer brushes reduces the translational entropy of the polymers and instead introduces an entropic penalty against stretching when vapor is absorbed. Therefore, swelling can be expected to be diminished in brushes compared to nongrafted films. Here, we study the effect of the anchoring-constraint on vapor sorption in polymer coatings using coarse-grained molecular dynamics simulations as well as humidity-controlled ellipsometry on chemically identical polymer brushes and nongrafted films. We find a qualitative agreement between simulations and experiments, with both indicating that brushes certainly swell less than physisorbed films, although this effect is minor for common grafting densities. Our results imply that polymer brushes indeed hold great potential for the intended applications.

The downscaling of electronic devices requires rechargeable microbatteries with enhanced energy and power densities. Here, we evaluate self-assembled vertically aligned nano-composite (VAN) thin films as a platform to create high-performance three-dimensional (3D) microelectrodes. This study focuses on controlling the VAN formation to enable interface engineering between the LiMn2O4 cathode and the (Li,La)TiO3 solid electrolyte. Electrochemical analysis in a half cell against lithium metal showed the absence of sharp redox peaks due to the confinement in the electrode pillars at the nanoscale. The (100)-oriented VAN thin films showed better rate capability and stability during extensive cycling due to the better alignment to the Li-diffusion channels. However, an enhanced pseudocapacitive contribution was observed for the increased total surface area within the (110)-oriented VAN thin films. These results demonstrate for the first time the electrochemical behavior of cathode-electrolyte VANs for lithium-ion 3D microbatteries while pointing out the importance of control over the vertical interfaces.

The microstructure of the PbZr0.52Ti0.48O3 (PZT) films is known to influence the ferroelectric properties, but so far mainly the effect of the deposition conditions of the PZT has been investigated. To our knowledge, the influence of the underlying electrode layer and the mechanisms leading to changes in the PZT microstructure have not been explored. Using LaNiO3 (LNO) as the bottom electrode material, we investigated the evolution of the PZT microstructure and ferroelectric properties for changing LNO pulsed-laser deposition conditions. The explored deposition conditions were the O2 pressure, total pressure, and thickness of the electrode layer. Increasing both the O2 pressure and the thickness of the electrode layer changes the growth of PZT from a smooth, dense film to a rough, columnar film. We explain the origin of the change in PZT microstructure as the increased roughness of the electrode layer in relaxing the misfit strain. The strain relaxation mechanism is evidenced by the increase in the crystal phase with bulk LNO unit cell dimensions in comparison to the crystal phase with substrate-clamped unit cell dimensions. We explain the change from a dense to a columnar microstructure as a result of the change in the growth mode from Frank−van der Merwe to Stranski−Krastanov. The ferroelectric properties of the columnar films are improved compared to those of the smooth, dense films. The ability to tune the ferroelectric properties with the microstructure is primarily relevant for ferroelectric applications such as actuators and systems for energy harvesting and storage.

With solar energy becoming a more and more common and a financially feasible method of generating electricity, along with it being renewable and sustainable, there is no doubt that it will be an important part of the future’s power generation. There is an enormous amount of solar power being provided to the earth constantly, more than 10 000 times the total energy consumption of the entire planet. This begs the question; is it possible to satisfy the global electricity demand with solar energy exclusively? This paper will attempt to answer this question, while narrowing the scope to installation of solar energy collection devices in the Sahara desert. The reason the Sahara desert is to be evaluated is due to the large amounts of solar irradiance it receives as well as the vast amounts of space available. Furthermore, a goal of 20 TWpeak to produce is defined, in order to future-proof the potential solution. Subjects covered in the paper include investigation into the location, different forms of electricity generation, the transportation of energy, political issues, as well as the expected environmental impact.

Here, we describe how to synthesise proton-conductive transition metal phosphates (TMPs) by direct thermal processing of precursor M-struvites, NH 4MPO 4·6H 2O, with M = Ni 2+, Co 2+. In the as-derived TMP phases their thermal history and bulk proton conductivity were linked with the structural information about the metal coordination, phosphate groups, and volatile compounds. These aspects were investigated with vibrational and synchrotron-based spectroscopic methods (FT-IR, FT-RS, XAS). We elucidated the structures of amorphous and crystalline Ni- and Co phosphate phases in association with different coordination changes and distortion degrees of the metal polyhedra as they developed upon heating. Ni-struvite transformed to a stable amorphous phase over a broad range of temperatures (90 °C < T < 600 °C), in which it remained in an octahedral coordination environment, but the degree of distortion changed with T. In contrast, heating of Co-struvite led to several successive crystalline phases with only unstable transitional and short-lived amorphous components. Among the as-occurring phases, a highly functional layered M-dittmarite NH 4MPO 4·H 2O obtained at low temperatures (T < 200 °C) demonstrated high proton conductivity values of 4.2 × 10 −5 S cm −1 for Ni-dittmarite and Co-dittmarite > 10 −4 S cm −1 at room temperature. Even at low humidity, these values are comparable with those found for Nafion, MOFs, some perovskites or composite materials. Coprecipitation of phosphates and transition metal cations in the form of struvite is potentially a viable method to extract these elements from wastewater. Thus, we propose that recycled M-struvites could be potentially further directly upcycled into crystalline and amorphous TMPs useful for electrochemical applications.

We are presenting a novel method to fabricate high aspect ratio, triangular cross-section solar cell front contacts, henceforth referred to as string-printing. We optimized string-printing to yield contacts with an aspect ratio larger than 1 and a light redirection efficiency or effective transparency of 67%, thereby mitigating most of the optical losses inherent to flat metallic front grids. In string-printing, a string coated with silver paste approaches a substrate until contact is made. Withdrawing the string then leaves behind silver paste on the substrate. Here, we describe the fabrication method and show initial results including current density-voltage curves of string-printed silicon heterojunction solar cells, as well as the effective transparencies of the contacts. String-printing is a scalable, low-temperature process with high potential to boost commercial solar cell efficiency and lower the module price per Watt.

We are reporting on high quality epitaxial thin films of [Pb(Mg1/3Nb2/3)O3]0.67-(PbTiO3)0.33 [PMN-PT (67/33)]. These films were deposited on (001) oriented, vicinal SrTiO3 single crystal substrates, using 1 mol. % niobium-doped Pb(Zr0.52,Ti0.48)O3 (Nb-PZT) as an interfacial layer. The functional properties of the epitaxial PMN-PT (67/33) thin films were investigated as a function of the layer thickness of the Nb-PZT layer. The deposited hetero-structures are perovskite phase pure and fully (001)-oriented. The variation in Nb-PZT interfacial layer thickness results in an increasing trend change of the in-plane lattice parameter of that layer, which in turn causes a decrease in the c/a ratio of the PMN-PT film on top. The most noticeable effect related to this is a decrease in built-in-bias (imprint) voltage. Thus, the built-in bias can be tuned by changing the interfacial layer thickness. The ferroelectric capacitor properties are found to be most stable for the thinnest interfacial layers under a high number (108) of switching cycles.

De Universiteit Twente (UT) haalt zes miljoen euro aan subsidies op voor de nog te bouwen fabriek New Origin. Daar worden zogenoemde fotonische chips gemaakt. Microchips van de volgende generatie, aangedreven door licht.

Wadsley-Roth phase titanium niobium oxides have received considerable interest as anodes for lithium ion batteries. However, the volume expansion and sluggish ion/electron transport kinetics retard its application in grid scale. Here, fast and durable lithium storage in entropy-stabilized Fe0.4Ti1.6Nb10O28.8 (FTNO) is enabled by tuning entropy via Fe substitution. By increasing the entropy, a reduction of the calcination temperature to form a phase pure material is achieved, leading to a reduced grain size and, therefore, a shortening of Li+ pathway along the diffusion channels. Furthermore, in situ X-ray diffraction reveals that the increased entropy leads to the decreased expansion along a-axis, which stabilizes the lithium intercalation channel. Density functional theory modeling indicates the origin to be the more stable Fe-O bond as compared to Ti-O bond. As a result, the rate performance is significantly enhanced exhibiting a reversible capacity of 73.7 mAh g(-1) at 50 C for FTNO as compared to 37.9 mAh g(-1) for its TNO counterpart. Besides, durable cycling is achieved by FTNO, which delivers a discharge capacity of 130.0 mAh g(-1) after 6000 cycles at 10 C. Finally, the potential impact for practical application of FTNO anodes has been demonstrated by successfully constructing fast charging and stable LiFePO4||FTNO full cells.

Their suggested stability towards high-voltage cathode materials makes halide-based solid electrolytes currently an interesting class of ionic conductors for solid-state batteries. Especially the LiMn2O4 spinel cathode active material is of interest due to its slightly higher nominal voltage and more resilience to overcharging compared to LiCoO2 and LiNixMnyCozO2 cathodes. Typically, a standard ratio of active material to solid electrolyte is used in composites for solid-state batteries. However, for ideal transport properties, and thus to achieve balanced and optimal partial-conductivities, this ratio needs to be re-optimized each time the material basis is changed. In this work, we show transport in the composite measured through both DC polarization as well as transmission line modeling of the impedance spectra. By balancing the partial transport parameters of the composite, an optimum capacity of the solid-state batteries is achieved. This work shows characterization and optimization of transport is required for unlocking the full potential of solid-state batteries.

The rapid advent of the piezoelectric microelectromechanical systems (PiezoMEMS) field has created a tremendous demand for low hysteretic piezoelectric thin films on Si. In this work, we present the integration of epitaxial Pb(Mg0.33Nb0.67)O3-PbTiO3 (PMN-PT) thin films with Si to enable device fabrication using state of the art methods. With optimized buffer layers and electronic contacts, high-quality low hysteretic PMN-PT thin films are integrated with Si, which is a significant stride towards employing PMN-PT thin film for PiezoMEMS devices. It is found that the processing of the necessary SrTiO3 buffer layer is crucial to achieve the growth of phase-pure perovskite PMN-PT layers on Si. Furthermore, we propose the engineering of the electronic contact for the PMN-PT-on-Si capacitors to obtain low hysteretic polarization and displacement responses.

Hematite (α-Fe 2O 3) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in the earth's crust. In this study, the photoexcited state of a hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at the PAL-XFEL in order to follow the dynamics of its photoexcited states. The 200 fs decay time of the hole state in the valence band was observed via its corresponding XAS feature.

Since thin-film silicon solar cells have limited optical absorption, we explore the effect of a nanostructured back reflector to recycle the unabsorbed light. As a back reflector we investigate a 3D photonic band gap crystal made from silicon that is readily integrated with the thin films. We numerically obtain the optical properties by solving the 3D time-harmonic Maxwell equations using the finite-element method, and model silicon with experimentally determined optical constants. The absorption enhancement relevant for photovoltaics is obtained by weighting the absorption spectra with the AM 1.5 standard solar spectrum. We study thin films either thicker ($L_{Si} = 2400$ nm) or much thinner ($L_{Si} = 80$ nm) than the wavelength of light. At $L_{Si} = 2400$ nm, the 3D photonic band gap crystal enhances the spectrally averaged ($\lambda = 680$ nm to $880$ nm) silicon absorption by $2.22$x (s-pol.) to $2.45$x (p-pol.), which exceeds the enhancement of a perfect metal back reflector ($1.47$ to $1.56$x). The absorption is enhanced by the (i) broadband angle and polarization-independent reflectivity in the 3D photonic band gap, and (ii) the excitation of many guided modes in the film by the crystal's surface diffraction leading to enhanced path lengths. At $L_{Si} = 80$ nm, the photonic crystal back reflector yields a striking average absorption enhancement of $9.15$x, much more than $0.83$x for a perfect metal, which is due to a remarkable guided mode confined within the combined thickness of the thin film and the photonic crystal's Bragg attenuation length. The broad bandwidth of the 3D photonic band gap leads to the back reflector's Bragg attenuation length being much shorter than the silicon absorption length. Consequently, light is confined inside the thin film and the absorption enhancements are not due to the additional thickness of the photonic crystal back reflector., Comment: 23 pages, 15 figures

The motion of domain walls is a crucial factor in piezoelectric properties and is usually related to the irreversible and hysteretic behaviors. Herein, we report on the investigation of inverse and transverse piezoelectric coefficients of capacitor-based and microcantilever-based Pb(Zr0.52Ti0.48)O3 films with a change in the DC bias and the AC applied voltage. A large inverse piezoelectric strain coefficient of about 350 p.m./V, and a low strain hysteresis of about 7.1%, are achieved in the film capacitors under a low applied voltage of 2 V (20 kV/cm) which can benefit the actuators for motion control in high-precision systems. The field-dependences of the transverse piezoelectric coefficients, obtained from four-point bending and microcantilever displacement, are in good agreement with each other. The results also reveal that the irreversible domain-wall motion is attributed to the nonlinearity in the field-dependent piezoelectric strain and cantilever displacement.

Transparent conducting oxides (TCOs) exhibit interesting linear and nonlinear optical properties in their epsilon-near-zero (ENZ) region. Studies so far have mostly focused on exploring the optical response of a limited number of these materials. It is therefore important to investigate new TCOs that could offer improved ENZ properties. This work reports for the first time measurements of the linear and nonlinear optical responses of polycrystalline indium-zirconium oxide (IZrO) in the ENZ spectral region. The fabricated IZrO films exhibit high optical mobility (>60 cm2 V-1 s-1) and a broadening of the ENZ region due to a graded permittivity along the thickness, as suggested by spectroscopic ellipsometry. This in turn leads to a broadband nonlinear response with a full-width-at-half-maximum bandwidth as large as ≈260 nm, covering the entire spectral range of the C, L, and U optical telecommunication bands. This work introduces IZrO as a new, promising TCO that could be used for ultrafast and broadband modulation of light in the telecommunication region of the spectrum.

With the rapid growth of the electric vehicle (EV) market, the number of Lithium-ion (Li-ion) batteries that reach their end of life (EOL) is increasing rapidly. Given the stringent capacity fading threshold of EV batteries, tools are required for better understanding and evaluating the health condition of large volume EV batteries that have reached EOL. In this paper, four modules from the same battery pack of a hybrid electric vehicle have been evaluated in terms of their current capacity and performance of the cells within each module. The results have been analyzed to find an affordable method for performance assessment of the retired batteries for echelon utilization. Electrochemical impedance spectroscopy (EIS) as an accurate and powerful technique has been used as a benchmark for the measurement to show the reliability of the tests. Experimental results are obtained from different test approaches on both modules and cell levels and show a different ageing degradation pattern for the cells inside the modules. The result shows that even for the modules with the same range of state of health, any non-uniformity of the cells inside the modules will affect the reliability of the modules for a second life. We also show there is a meaningful dependency between the voltage monitoring of the cells and other test approaches to determine the uniformity of a module.

Key technologies in energy conversion and storage, sensing and chemical synthesis rely on a detailed knowledge about charge transfer processes at electrified solid-liquid interfaces. However, these interfaces continuously evolve as a function of applied potentials, ionic concentrations and time. We therefore need to characterize chemical composition, atomic arrangement and electronic structure of both the liquid and the solid side of the interface under operating conditions. In this chapter, we discuss the state-of-the-art X-ray based spectroscopy and diffraction approaches for such “operando” characterization. We highlight recent examples from literature and demonstrate how X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and surface X-ray diffraction can reveal the required interface-sensitive information.

Correlated metals with high carrier density and strongly correlated electron effects provide an alternative route to achieve transparent conducting materials, different from the conventional degenerately doped wide-bandgap transparent conducting oxides (TCO). The extremely low electrical resistivity and high optical transparency in the ultraviolet-visible spectral range shown in 4d correlated metals present an advantage over conventional TCOs. However, most of the 4d correlated metals are grown epitaxially on single crystal substrates. Here, it has been shown that Ca2Nb3O10 nanosheets with different buffer layers promote the growth of high-quality 4d2 SrMoO3 films on fused silica substrates, overcoming the use of expensive and size-limited single-crystal substrates. The room temperature electrical resistivity of SrMoO3 is as low as 61 µΩ cm, the lowest reported value on amorphous transparent substrates to date, without compromising its high optical transmittance. 4d1 correlated metal SrNbO3 on Ca2Nb3O10 nanosheets also exhibits similarly high optical transmittance but a higher room temperature resistivity of 174 µΩ cm. These findings facilitate the use of highly conducting and transparent 4d correlated metals not only as TCOs on technologically relevant substrates for the applications in the ultraviolet-visible spectral range but also as electrodes for other oxide-based thin film technologies.

This thesis contains two parts, namely (1) the structural design of niobium-based oxides for fast-charging battery applications and (2) the investigation of different influences ranging from the intrinsic material properties to the diffusion behavior of the lithium-ions into these niobium-based materials. The first part includes the investigation on three novel niobium based fast charging electrode materials, niobium tungsten oxide, nickel niobium oxide, niobium tungsten oxide 2D glass micro-electrode on conductive substrate. The second part contains a new theoretical framework for decoupling the influences of ohmic resistance, reaction rate, and ion diffusion to the fast-charging properties of the electrode materials. And this model was used to study the electrochemical origins of the fast charging performance of the niobium-based electrode materials.

Solar photovoltaic (PV) energy plays a pivotal role in the quest for achieving a sustainable and greener future. Increasing the yield of PV modules will not only help in meeting the everincreasing global electricity demands, but also make the PV more economically lucrative, as compared to other sources. Bifacial modules offer an effective way to increase the power generation by accepting the solar irradiance from both faces, i.e., front and rear. The yield of the module depends on the spectral [1] and angular [2] composition of the light incident on it. The spectro-angular composition of the irradiance in outdoor conditions depends on numerous factors, such as, the geographical location [1], time of the day [4] and year [5], climate [6], weather [7], cloud coverage [8], atmospheric conditions, and the reflectors [1] or surroundings. This leads to serious complications in irradiance modeling and, consequently, in PV yield modeling as the input irradiance influences the PV output. Measuring the spectro-angular irradiance helps in addressing this issue. A high-quality hour- or minute-resolved year-long spectro angular irradiance data will help in verifying and training existing and emerging models. Finally, to boost bifacial yield, understanding and optimizing the reflectors become vital. This thesis offers solutions for the above two challenges.

An alliance of photovoltaic manufacturers is creating a certification standard to differentiate modules containing high (10 g CO2 eq./kWh) or low (5 g CO2 eq./kWh) embodied CO2. If new standards lead to project installation delays, this can pose serious threats for achieving CO2 avoidance targets. We calculate CO2 emission burdens of delaying coal and combined cycle gas (CCG) replacements. These show delays of < 3 months (coal) and

We present the concept of interference solar cells for enhanced absorption in thin (

Lead-free ferroelectric sol-gel thin films derived from barium strontium titanate (Ba0.85Sr0.15Zr0.1Ti0.9O3, BSZT) were deposited onto two types of electrode: (i) noble metallic Pt- and (ii) conductive oxides LaNiO3- and SrRuO3-coated silicon substrates. The present studies demonstrate that electrode materials impact significantly on morphology, crystallographic orientation, lattice mismatch-induced microstrains and electrical properties of BSZT thin films. Highly (100)-textured BSZT thin films with the highest crystallinity and lowest microstrain were found on conductive oxide electrodes, whereas Pt electrodes showed polycrystalline. Capacitors with oxide LaNiO3 electrode display predominated Schottky emission with a rather low leakage current density ~4.68 × 10−8 A/cm2, while Pt electrode capacitors indicate space-charge limited conduction. Dielectric characterizations in the frequency range of 103–5 × 106 Hz and the dc electric field up to ±800 kV/cm show that the permittivity, loss tangent, and tunability of BSZT films also strongly depend on the electrode materials used. The optimal dielectric tunability with a large figure of merit (FOM ≈ 22.53) and low dielectric loss ( t a n δ ≈ 2.9%), was found to be 66% for BSZT thin films on the conductive LaNiO3 electrode, suggesting that the as-deposited ferroelectric films are promising candidates for applications in tunable microwave elements and related electronic devices.

As the employment of halide perovskite films in single-junction and tandem solar cells continues to soar, there is a strong drive -from academia to industry- to produce these films using dry processes, avoiding the use of toxic solvents. Vapor deposition methods such as co-evaporation have shown advantages of solvent-free approaches to produce high-efficiency solar cells. However, co-evaporation requires the use of multiple sources that challenge the deposition rate control of complex halide perovskite compositions. Here, Pulsed Laser Deposition (PLD) is proposed as an alternative method to deposit hybrid halide perovskites films from a single-source and following a fully dry approach. We use the archetypical methylammonium lead iodide (MAPbI3) to demonstrate the formation of high-quality films with optimal optoelectronic properties by PLD on various substrates for single-junction and tandem devices. Furthermore, the important role of the PLD target composition and deposition parameters to achieve control over film microstructure and optoelectronic properties is discussed. The controlled conformal growth provided by PLD demonstrated in this work with MAPbI3 on device-relevant substrates will broaden opportunities to explore PLD of more complex hybrid halide perovskite compositions for efficient, stable, and scalable solar cell devices.

Thin, flexible, and efficient silicon solar cells would revolutionize the photovoltaic market and open up new opportunities for PV integration. However, as an indirect semiconductor, silicon exhibits weak absorption for infrared photons and the efficient absorption of the full above bandgap solar spectrum requires careful photon management. This review paper provides an overview on the fundamental physics of light trapping and explains known theoretical limits. Technologies that have been developed to improve light trapping will be discussed, and limitations will be addressed.

Multilayer thin-film dielectric capacitors with high energy-storage performance and fast charge/discharge speed have significantly affected the development of miniaturized pulsed-power devices. Here, the interfacial strain in epitaxial multilayers of antiferroelectric PbZrO3 and relaxor-ferroelectric Pb0.9La0.1Zr0.52Ti0.48O3 is shown to significantly enhance the maximum polarization of the multilayer thin-film capacitors, beyond that of the composing individual layers. Insights obtained from atomically resolved energy-dispersive X-ray spectroscopy and high-resolution X-ray diffraction analysis of the interface and domain structure are used to develop phenomenological models that explain the observed trends in breakdown strength and energy-storage density as a function of multilayer period number. The underlying mechanism is the mechanical coupling between the layers that depends on the individual layer thicknesses. These factors result in a strongly enhanced recoverable energy-storage density (increased by a factor of 4 to ≈128.4 J cm−3) with high efficiency (≈81.2%). Moreover, the multilayer films show almost fatigue-free energy-storage performance after 1010 switching cycles, even at elevated temperatures up to 220 °C, demonstrating their robustness. The outstanding properties show the great potential of epitaxial multilayers for energy-storage applications, due to the well-defined separate layers and coupling of properties across the interfaces, not present in ceramic composites.

Nanoparticle formation by dopant exsolution (migration) from bulk host lattices is a promising approach to generate highly stable nanoparticles with tunable size, shape, and distribution. We investigated Ni dopant migration from strontium titanate (STO) lattices, forming metallic Ni nanoparticles at STO surfaces. Ex situ scanning probe measurements confirmed the presence of nanoparticles at the H2 treated surface. In situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) revealed reduction from Ni2+ to Ni0 as Ni dopants migrated to the surface during heating treatments in H2. During Ni migration and reduction, the Sr and Ti chemical states were mostly unchanged, indicating the selective reduction of Ni during treatment. At the same time, we used in situ ambient pressure grazing incidence X-ray scattering (GIXS) to monitor the particle morphology. As Ni migrated to the surface, it nucleated and grew into compressed spheroidal nanoparticles partially embedded in the STO perovskite surface. These findings provide a detailed picture of the evolution of the nanoparticle surface and subsurface chemical state and morphology as the nanoparticles grow beyond the initial nucleation and growth stages.

The stability of perovskite oxide catalysts for the oxygen evolution reaction (OER) plays a critical role for their applicability in water splitting concepts. Decomposition of perovskite oxides under applied potential is typically linked to cation leaching and amorphization of the material. However, structural changes and phase transformations at the catalyst surface were also shown to govern the activity of several perovskite electro-catalysts under applied potential. Hence, it is crucial for the rational design of durable perovskite catalysts to understand the interplay between the formation of active surface phases and stability limitations under OER conditions. In the present study, we reveal a surface-dominated activation and deactivation mechanism of the prominent electrocatalyst La0.6Sr0.4CoO3-ẟ under steady-state OER conditions. Using a multi-scale micros-copy and spectroscopy approach, we identify evolving Co-oxyhydroxide as catalytically active surface species and La-hydroxide as inactive species involved in the transient degradation behavior of the catalyst. While the leaching of Sr results in the formation of mixed surface phases, that can be considered as a part of the active surface, the gradual depletion of Co from a self-assembled active CoO(OH) phase and the relative enrichment of passivating La(OH)3 at the electrode surface results in the failure of the perovskite catalyst under applied potential.

Most materials can be classified either as electric conductors or as insulators. Only a few materials possess the ability to switch their character depending on the conditions to which they are subjected. One of the exotic materials that can reversibly transition between a conducting state and an insulating state is vanadium dioxide (VO2). In VO2, the electronic phase transition is directly connected to a structural phase transition from a monoclinic symmetry at low temperatures to a tetragonal, rutile symmetry at high temperatures. Among the many figurative knobs that can be turned to alter the properties of materials, strain or pressure stands out as a particularly powerful parameter. The strong coupling of the lattice and electronic degrees of freedom of VO2 was used to mechanically induce the phase transition at room temperature. A controlled amount of pressure was applied along the rutile c-axis of a VO2 film by a nanosized metallic probe in an atomic force microscope. The phase transition was reversibly triggered at a critical pressure, as witnessed by a sizeable conductivity modulation. The pressure needed to induce the transition decreased with increasing temperature, and the phase coexistence line that separates the insulating and metallic phases was determined in a hitherto unexplored regime. Furthermore, it was illustrated how four-dimensional scanning transmission electron microscopy (4D STEM) combined with electron energy loss spectroscopy (EELS) could be used to investigate both the structural and the electronic phase transition of VO2 with nanometer spatial resolution. Thereby, it was possible to image and track the metal-insulator transition of individual domains of VO2 as they nucleated and grew during heating and cooling cycles. In addition, the samples were analyzed by microfocus X-ray diffraction at various temperatures across the phase transition to quantify the lattice parameters.

The oxygen evolution reaction (OER) is one of the key kinetically limiting half reactions in electrochemical energy conversion. Model epitaxial catalysts have emerged as a platform to identify structure-function-relationships at the atomic level, a prerequisite to establish advanced catalyst design rules. Previous work identified an inverse relationship between activity and the stability of noble metal and oxide OER catalysts in both acidic and alkaline environments: The most active catalysts for the anodic OER are chemically unstable under reaction conditions leading to fast catalyst dissolution or amorphization, while the most stable catalysts lack sufficient activity. In this perspective, we discuss the role that epitaxial catalysts play in identifying this activity-stability-dilemma and introduce examples of how they can help overcome it. After a brief review of previously observed activity-stability-relationships, we will investigate the dependence of both activity and stability as a function of crystal facet. Our experiments reveal that the inverse relationship is not universal and does not hold for all perovskite oxides in the same manner. In fact, we find that facet-controlled epitaxial La0.6Sr0.4CoO3-δ catalysts follow the inverse relationship, while for LaNiO3-δ, the (111) facet is both the most active and the most stable. In addition, we show that both activity and stability can be enhanced simultaneously by moving from La-rich to Ni-rich termination layers. These examples show that the previously observed inverse activity-stability-relationship can be overcome for select materials and through careful control of the atomic arrangement at the solid-liquid interface. This realization re-opens the search for active and stable catalysts for water electrolysis that are made from earth-abundant elements. At the same time, these results showcase that additional stabilization via material design strategies will be required to induce a general departure from inverse stability-activity relationships among the transition metal oxide catalysts to ultimately grant access to the full range of available oxides for OER catalysis.