Search

A hybrid photovoltaic-thermal (PVT) system combines photovoltaic (PV) and photo-thermal (PT) energy collection into a single structure, enhancing the potential to achieve greater solar energy conversion efficiencies. Such enhanced efficiencies can result in greater economic returns and could promote a larger uptake of PVT devices in cold and temperate climate countries. Through the utilization of a Monte Carlo ray-tracing model, this work provides new insights into the optical, electrical, and thermal characteristics of PVT devices. In particular, the work focuses on evaluating the behaviour of novel luminescent imidazole-phenanthroline-based working fluids that were previously experimentally investigated as liquid spectral beam splitters (SBS). The modelling procedure outlined here is able of providing an in-depth analysis of various categories of photons undergoing events such as transmission, absorption, parasitic absorption, and luminescent downshifting (LDS) which, otherwise, are difficult or impossible to detect experimentally. Evaluating such photon characteristics provides the possibility to estimate the direct contribution of the luminophore (embedded within the working fluid) to the enhanced conversion efficiencies reported for PVT systems. In addition, the model can also allow for better tuning of the luminophore properties to match the main factors that are influencing the energy conversion dynamics of these systems. The current results indicate that the embedded luminophore is able of providing direct contributions of up to 91% for thermal power generation and 77% towards electrical power generation for the various concentrations of the liquid filters when compared with the individual performances of the independent PV or PT systems.

The development of highly efficient solar collectors requires modulating the light interactions with the semiconducting materials. Incorporating luminescent species and metal nanoparticles within a semitransparent polymeric material (e.g., polymethyl methacrylate (PMMA)) leads to the formation of a plasmon-enhanced luminescent down-shifting (PLDS) layer, which offers a retrofittable approach toward expanding the wavelength range over which the conversion process can effectively occur. Adding antireflection coatings (ARCs) further controls the spectral response. However, with each additional component comes additional loss pathways. In this study, the losses related to light interactions with the PMMA and the ARCs have been investigated theoretically using a transfer matrix method and experimentally validated. Two proposed architectures were considered, and the deviations between the optical response of each iteration helped to establish the design considerations. The proposed structure-enhanced (SE) designs generated a predicted enhancement of 37 to 62% for the collection performance of a pristine monocrystalline-silicon solar cell, as inferred through the short-circuit current density (Jsc). The results revealed the synergies among the SE-design components, demonstrating that the spectral response of the SEs, containing a thin polymer framework and an ARC, can be tuned to minimize the reflections, leading to the solar energy conversion enhancement.

High-sensitivity and simple, low-cost readout are desirable features for sensors independent of the application area. Micro-cantilever sensors use the deflection induced by the analyte presence to achieve high-sensitivity but possess complex electronic readouts. Current holographic sensors probe the analyte presence by measuring changes in their optical properties, have a simpler low-cost readout, but their sensitivity can be further improved. Here, the two working principles were combined to obtain a new hybrid sensor with enhanced sensitivity. The diffractive element, a holographically patterned thin photopolymer layer, was placed on a polymer (polydimethylsiloxane) layer forming a bi-layer macro-cantilever. The different responses of the layers to analyte presence lead to cantilever deflection. The sensitivity and detection limits were evaluated by measuring the variation in cantilever deflection and diffraction efficiency with relative humidity. It was observed that the sensitivity is tunable by controlling the spatial frequency of the photopolymer gratings and the cantilever thickness. The sensor deflection was also visible to the naked eye, making it a simple, user-friendly device. The hybrid sensor diffraction efficiency response to the target analyte had an increased sensitivity (10-fold when compared with the cantilever or holographic modes operating independently), requiring a minimum upturn in the readout complexity.

The high sensitivity of silicon microcantilever sensors has expanded their use in areas ranging from gas sensing to bio-medical applications. Photochromic molecules also represent promising candidates for a large variety of sensing applications. In this work, the operating principles of these two sensing methods are combined in order to detect the reversible conformational change of a molecular switch, spiropyran. Thus, arrays of silicon microcantilever sensors were functionalized with spiropyran on the gold covered side and used as test microcantilevers. The microcantilever deflection response was observed, in five sequential cycles, as the transition from the spiropyran (SP) (CLOSED) to the merocyanine (MC) (OPEN) state and vice-versa when induced by UV and white light LED sources, respectively, proving the reversibility capabilities of this type of sensor. The microcantilever deflection direction was observed to be in one direction when changing to the MC state and in the opposite direction when changing back to the SP state. A tensile stress was induced in the microcantilever when the SP to MC transition took place, while a compressive stress was observed for the reverse transition. These different type of stresses are believed to be related to the spatial conformational changes induced in the photochromic molecule upon photo-isomerisation.

Exploiting solar energy using photo-thermal (PT) and/or hybridised photovoltaic/thermal (PVT) systems can represent a viable alternative to the growing demand for renewable energy. For large-scale implementation, such systems require thermal fluids able to enhance the combined conversion efficiency achievable by controlling the &lsquo, thermal&rsquo, and &lsquo, electrical&rsquo, components of the solar spectrum. Nanofluids are typically employed for these purposes and they should exhibit high heat-transfer capabilities and optical properties tuned towards the peak performance spectral window of the photovoltaic (PV) component. In this work, novel nanofluids, composed of highly luminescent organic molecules and Ag nanoparticles dispersed within a base fluid, were tested for PT and PVT applications. These nanofluids were designed to mimic the behaviour of luminescent down-shifting molecules while offering enhanced thermo-physical characteristics over the host base fluid. The nanofluids&rsquo, conversion efficiency was evaluated under a standard AM1.5G weighted solar spectrum. The results revealed that the Ag nanoparticles&rsquo, inclusion in the composite fluid has the potential to improve the total solar energy conversion. The nanoparticles&rsquo, presence minimizes the losses in the electrical power component of the PVT systems as the thermal conversion increases. The enhanced performances recorded suggest that these nanofluids could represent suitable candidates for solar energy conversion applications.

Nanofluids offer the potential to address the low thermal conductivities found in conventional heat transfer fluids, through their unique electrical, optical and thermal properties, but their implementation remains restricted due to absorption and stability limitations. Here, we characterize and exploit the distinctive plasmonic properties exhibited by polyvinyl-alcohol stabilized silver nanostructures by tuning their absorption and thermal properties through controlling the nanoparticle size, morphology and particle-size distribution configuration at the synthesis stage. The photo-thermal efficiency of different water-based silver nanofluids under a standard AM1.5G weighted solar spectrum were explored, the influence of each of these components on the resulting fluids performance within a direct absorption solar thermal collection system being considered. Nanofluids, containing an extensive ensemble of particle size-distributions (5 nm–110 nm in diameter) in addition to anisotropic particle morphologies (e.g. prisms, hexagons and other non-spherical geometries), exhibited a significant enhancement in the absorption and photo-thermal energy transfer. Enhancements of 5%–32% in the photo-thermal conversion efficiency were achieved, the enhancement being dependent upon the presence of multiple particle size-distributions and the particle concentration. The enhancement is influenced by the interactions occurring between the individual particle size-distributions but also by the collective behaviour of the particles ensemble. The critical particle diameter, above which the photo-thermal characteristics of the nanofluid become dominated by the larger sized particles present, was identified as 150 nm. The increased performance of these nanofluids, which adopt a more complex particle-size configuration, suggests that they can represent suitable candidates for solar-thermal applications.

Plasmon enhanced luminescent down-shifting (PLDS) represents a passive design strategy in which the narrow spectral responsivity of photovoltaics (PVs) is increased through the application of a semi-transparent, fluorescent, polymer nanocomposite encapsulation. However, the additional loss pathways facilitated through the integration of the PLDS layer into the optical system must be overcome for the retrofitted structure to offer an enhancement to the underlying PV-device. In this study, through exploiting the antireflection properties of thin films and PLDS coatings, some of these loss mechanisms were addressed using a transfer matrix model. Two initial designs of this structure enhanced (SE) PLDS architecture were developed for a monocrystalline silicon (mc-Si) PV device using Ag nanoparticles to modify the properties of the poly (methyl-methacrylate) - PMMA encapsulation and antireflection coatings (ARC). Through the careful consideration of the composition and optical thickness of the ARC and the position at which it is integrated within the stratified SE-PLDS architecture, a 52% enhancement of the photocurrent is predicted to be produced, as compared to the conventional PV-device. Reducing the SE-PLDS layer's thickness further extended the improvement up to a 55% total enhancement in the mc-Si cell electrical generating capacity, even in the absence of plasmon assisted photoluminescence.

Hybridised photovoltaic-thermal (PVT) systems, obtained by merging photo-voltaic (PV) and photo-thermal (PT) technologies, can lead to enhanced conversion efficiencies. Liquid spectral beam splitters (SBSs) offer control of the ‘thermal’ and ‘electrical’ components of the solar spectrum. Combining PVT systems with liquid SBSs facilitates enhanced control of the thermal and electrical outputs, further improving the PVT systems efficiency and making them economically viable. Traditionally, liquid SBSs contain nanostructures suspended in a base-fluid to capitalise on the enhanced heat transfer capabilities offered by the nanostructures' surface morphology. These nanofluids have certain disadvantages, such as stability problems, environmental hazards and synthetic cost concerns, which preclude them from becoming a viable substitute for commercial (single-phase) fluids. This study offers an alternative strategy by employing a set of newly developed fluids containing organic and organometallic imidazo[4,5-f][1,10]phenanthroline derivatives for SBS-PVT systems. These new working fluids were designed to mimic the behaviour of luminescent down-shifting (LDS) molecules while offering enhanced thermophysical characteristics over the host base-fluid. Their optical, fluorescent and thermophysical properties enabled an increased heating rate within the working fluid. Their integration as working fluids in an SBS-PVT system lead to optical efficiencies of ~63% i.e. an 18%–20% improvement over the standalone PV technology. The fluid properties displayed a 61% increase in the economic value of the energy captured when compared to the host base-fluid alone for the same PVT system. Consequently, these novel fluids and the organic molecules they contain can be effectively designed as high performance spectrally selective fluids for PVT applications.

The industrial sector of flexible printed electronics has shown a dynamic growth in the last decades. Therefore, demand for new inks, coatings and printing methods leading to improved performances of the electronic components at room temperature is also increasing. Here, we present a study on the conductive properties of silver layers obtained by different coating and printing methods. The results obtained proved that drop-on-demand inkjet printing of water-based inks containing micron-sized silver flakes with narrow-size distribution is a feasible method for in situ fabrication of conductive silver coatings that does not require additional heat treatment. A rigorous optimization Taguchi experiment was carried out considering the major process parameters. This experiment showed that the printing pressure was the dominant factor defining the quality of the printed coatings and tracks.

The stability of thin poly(methyl-methacrylate) (PMMA) films of low molecular weight on a solid substrate is controlled by the areal coverage of gold nanoparticles (NPs) present at the air-polymer interface. As the polymer becomes liquid the Au NPs are free to diffuse, coalesce, and aggregate while the polymer film can change its morphology through viscous flow. These processes lead at the same time to the formation of a fractal network of Au NPs and to the development of spinodal instabilities of the free surface of the polymer films. For thinner films a single wavelength is observed, while for thicker films two wavelengths compete. With continued heating the aggregation process results in a decrease in coverage, the networks evolve into disordered particle assemblies, while the polymer films flatten again. The disordering occurs first on the smallest scales and coincides (in thicker films) with the disappearance of the smaller wavelength. The subsequent disordering on larger scales causes the films to flatten.

The requirement for low-cost access to energy storage technologies is increasing with the continued growth of renewable energy. The growth of the hydrogen economy is also expected to emerge to improve energy security and meet the growing pressures of environmental requirements. Hydrogen and redox flow batteries (RFB) have promising energy storage characteristics that can allow increased penetration of renewable energy and reduction in grid energy. The strong synergy between natural gas and hydrogen anticipates that new efficient methods of hydrogen production such as microwave plasma processing of natural gas might have a leading role. Additionally, the improvements in the carbon allotropes properties and their cost are expected to influence large-scale energy storage system costs. A technical and economic comparison of vanadium and all-iron RFB with hydrogen will be explored on an individual and integrated basis. The findings show hydrogen’s capability for bulk energy storage and highlights the benefits ...

peer-reviewed Thin and ultrathin polymer films combined with nanoparticles (NPs) are of significant interest as they are used in a host of industrial applications. In this paper we describe the stability of such films (hpoly ≤ 30 nm) to dewetting, specifically, how the development of a spinodal instability in a composite NP–polymer layer is controlled by the embedding of Au NPs. At working temperatures (T = 170 °C) above the polymer glass transition temperature (Tg ≈ 100 °C) the absence of Au NPs leads to film rupture by nucleation dewetting, while their presence over a large surface area enhances the development of a spinodal instability without destroying the film continuity. When the NPs embed, the surface undulations are suppressed. The dynamics change from an unstable to a stable state, and the thin composite NP–polymer layer returns to a flat configuration, while the wavelength of the pattern remains constant. Moreover, we demonstrate from a thermodynamic perspective that NPs will remain on the surface or embed in the polymer film depending on their free energy, which is determined by the NP interactions with the underlying polymer, the native SiOx layer, and the Si substrate. peer-reviewed

We demonstrate control, via electro-hydrodynamic (EHD) induced polymer instabilities and nanoparticle mobility, of hierarchical fractal arrangements of gold nanoparticles on patterned thin polymer films. The induced changes in the film curvature enhance fractal formation for high and not for low mobility nanoparticles. The high mobility nanoparticles cluster in circular fractal networks on the rims of a hexagonally ordered array of EHD-induced polymer peaks. These arrangements exhibit plasmonic properties for surface-enhanced Raman scattering (SERS) spectroscopy.

The stability of polystyrene thin films of low molecular weight on a solid substrate is shown to be controlled by the presence of uniformly distributed gold sputtered at the air–polymer interface. Continuous gold coverage causes the formation of wrinkles. High coverage and Au nanoparticle (NP) density leads to the development of a spinodal instability while low coverage and NP density retards the nucleation dewetting mechanism that beads up the thin polymer film into drops when no coverage is present. Heating at temperature larger than the polymer glass transition temperature for extended periods allows the gold NPs to coalesce and rearrange. The area of polymer surface covered by NPs decreases as a result and this drives the films from unstable to metastable states. When the gold NPs are interconnected by polymer chains a theoretically predicted spinodal instability that patterns the film surface is experimentally observed. Suppression of the instability and a return to a flat film occurs when the polymer interconnections between particles are broken. While the polymer films maintain their physical continuity changes in their chemical surface composition and thickness are observed. The observed film metastability is nevertheless in agreement with theoretical prediction that includes these surface changes.

peer-reviewed Direct coating methods using metal particles from aqueous solutions or solvent-based inks become central in the roll-to-roll fabrication processes as these methods can lead to continuous or pre-defined conductive layers on a large variety of substrates. For good electrical conductivity, the metal particles have to be brought into contact, and traditionally, additional sintering treatments are required. Such treatments can degrade the sensitive substrates as paper or polymer films. In this study, the possibility of obtaining conductive layers at room temperature is investigated for direct coating methods with an emphasis on drop-casting and inkjet printing. Thus, it is shown that electrical conductive layers can be achieved if the metal particles can compact during the drop-substrate impact interaction. It is theoretically shown that the compaction process is directly related to the particle and ink drop size, the initial fractional particle loading of the ink, solvent viscosity, and drop velocity. The theoretical predictions on compaction are experimentally validated, and the particle compaction's influence on changes in the electrical conductivity of the resulting layers is demonstrated. (C) 2016 AIP Publishing LLC. PUBLISHED peer-reviewed

International audience; Strong electric fields produce forces that can overcome the surface tension in thin liquid polymer films and in this way induce an instability of the free surface of the film, that triggers the formation of structures on a micrometer length scale. Here, we study experimentally a polymer–air–polymer system for several combinations of polymer films. These results are accompanied by theoretical considerations based on coupled long-wave time evolution equations for the two free surface profiles. The linear stability and nonlinear time evolution are investigated and compared to the experimental findings. The prediction that the instability always evolves through a mirror mode that couples the two surfaces in an anti-phase manner agrees well with the experimental results. The model describes well the linear (early stage) evolution of the instability. In the non-linear (later stage) evolution, topographical differences in the instability pattern occur if the mobilities of the two layers significantly differ and an unpredicted acceleration of growth is seen in thinner less mobile films. Possible reasons for the mismatch are discussed.

Emissive probes are standard tools in laboratory plasmas for the direct determination of the plasma potential. Usually they consist of a loop of refractory wire heated by an electric current until sufficient electron emission. Recently emissive probes were used also for measuring the radial fluctuation-induced particle flux and other essential parameters of edge turbulence in magnetized toroidal hot plasmas [R. Schrittwieser et al., Plasma Phys. Controlled Fusion 50, 055004 (2008)]. We have developed and investigated various types of emissive probes, which were heated by a focused infrared laser beam. Such a probe has several advantages: higher probe temperature without evaporation or melting and thus higher emissivity and longer lifetime, no deformation of the probe in a magnetic field, no potential drop along the probe wire, and faster time response. The probes are heated by an infrared diode laser with 808 nm wavelength and an output power up to 50 W. One probe was mounted together with the lens system on a radially movable probe shaft, and radial profiles of the plasma potential and of its oscillations were measured in a linear helicon discharge.