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Numerical investigation of energy performance and cost analysis of Moroccan’s building smart walls integrating vanadium dioxide
摘要： Thermochromic materials such as vanadium dioxide (VO2) have the capability to regulate their infrared reflectivity depending on ambient temperature. Such smart materials are attractive for applications like smart windows and smart roofs. In this paper, we investigate numerically the impact of tungsten (W) doped VO2 application as a smart outdoor wall layer on the building energy consumption in the Mediterranean climate. Temperature distributions through wall configurations with and without W doped VO2 were calculated using finite differences method implemented in Matlab environment. Calculations take into consideration dynamic variations of W doped VO2 absorptivity depending on outdoor temperature variations. Decrement factor, time lag, transmission and peak loads of cooling and heating were calculated. Results have shown that the indoor surface temperature is attenuated during summer by 2–3 °C depending on orientation. Cooling energy saving due to the use of W doped VO2 in summer is around 70% monthly which is equivalent to save $21.6/month of electricity invoiced amount. During winter, W doped VO2 maintains the same value of absorptivity as the uninsulated wall. Thus, results show small differences for indoor surface temperature and heating energy consumption. The application of W doped VO2 in intelligent thermal wall insulation offers a real-time dynamic variation of building’s envelope solar absorptivity and makes smart walls concept more feasible.
关键词： Energy efficiency,Smart wall,Radiative thermal rectification,Thermochromic,Real-time dynamic absorptivity,Vanadium dioxide
更新于2025-09-23 15:23:52
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Broadband light-trapping enhancement of graphene absorptivity
摘要： Low optical absorptivity of graphene limits the quantum efficiency of graphene-based optoelectronic devices. We demonstrate a broadband enhancement of absorptivity in an architecture of graphene intercalation inside a simple-cubic woodpile photonic crystal. Significant light-trapping effect is achieved due to spectrally broad and dense resonances in the architecture, especially modes propagating nearly parallel to the interface between the photonic crystal and the background material. We demonstrate an overall absorptivity ～10 to 17 times larger than the free-standing bare graphene monolayer with bandwidth to central frequency ratio 0.3, and ～5 to 11 times larger with bandwidth to central frequency ratio 1.33. A distributed intercalation of three graphene monolayers proves a ～70% overall absorptivity with bandwidth to central frequency ratio 0.3.
关键词： absorptivity,broadband enhancement,graphene,light trapping,photonic crystal
更新于2025-09-23 15:23:52
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Interfacial engineering revolutionizers: perovskite nanocrystals and quantum dots accentuated performance enhancement in perovskite solar cells
摘要： Utilization of efficient nanomaterials in perovskite solar cells (PSCs) for effectual conversion of solar energy to electrical energy has prompted the extensive progression of PSCs as a suitable alternative to silicon-based photovoltaic (PV) technologies. Most recent progressions are inclusive of nanoscale materials incorporation particularly nanocrystals (NCs) and quantum dots (QDs) with unique sizes, morphological and compositional aspects aimed at PSCs modification. In all conventional architectures of the PSCs, there are number of interfaces between the transport layers and active absorber perovskite layer. Nanocrystals and quantum dots have been employed for the interfacial engineering in PSCs owing to their remarkable optoelectronic and photo-physical characteristics favoring the facile and efficient power generation and reducing dependence on silicone-based PVs. Myriad of NCs and QDs having inorganic and/or inorganic perovskite composition have been investigated, however, the overall synthetic costs, procedural complications, current, and voltage (J–V) hysterical response and stability toward air and light needs further meticulous investigations due to which PV community has been disseminating experimental results rapidly since last few years. Considering the potential of perovskite NCs and QDs, current review has for the first time explored the most recent progressions done in utilization of these nanoscale materials in augmenting PSCs PV functionality through interface modification. Magnifying extent of nanoscale materials for PSCs modification and current investigation signifies the future candidacy of perovskite NCs and QDs as humanity gallants for provisioning of cheaper and sustainable power sources.
关键词： Absorptivity,photovoltaics,bandgap,diffusion length,charge transfer
更新于2025-09-23 15:21:01
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Laser metal deposition of copper on diverse metals using green laser sources
摘要： Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.
关键词： Multi-material,DED,High-speed imaging,LMD,Copper,Green 515-nm laser,Laser metal deposition,Powder grain incorporation,Additive manufacturing,Directed energy deposition,Absorptivity
更新于2025-09-19 17:13:59
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Conical microstructuring of titanium by reactive gas assisted laser texturing
摘要： Femtosecond laser micromachining is an important and flexible method to generate precisely targeted surfaces on various materials. On titanium, the laser structuring process strongly depends on the laser parameters. For example, an increasement of the pulse length and repetition rate favors melting processes instead of ablation and microstructuring. We report on an investigation of reactive halogens (iodine, bromine, chlorine) and halocarbons as additives to the laser structuring process of pure titanium and the common alloy Ti-6Al-4V with 0.75 ps laser pulses. The choice of the halogen allows control of whether solely the chemical composition or the surface microstructure should be altered. Bromine was found to be an efficient additive to generate homogeneous microstructures based on micropillars at convenient conditions (air, atmospheric pressure). The resulting surfaces have been characterised by thermal emission infrared photography, scanning electron microscopy, energy dispersive X-ray spectroscopy, reflective UV/Vis spectroscopy and contact angle measurements. The bromine/air processed titanium surfaces revealed superhydrophilicity, strongly increased thermal emissivity and a high absorptivity (“black metal”).
关键词： Superhydrophilicity,Reactive halogens,Absorptivity,Titanium,Femtosecond laser micromachining,Microstructuring,Thermal emissivity
更新于2025-09-16 10:30:52
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Spatially and Spectrally Resolved Absorptivity: New Approach for Degradation Studies in Perovskite and Perovskite/Silicon Tandem Solar Cells
摘要： Instability in perovskite solar cells is the main challenge for the commercialization of this solar technology. Here, a contactless, nondestructive approach is reported to study degradation across perovskite and perovskite/silicon tandem solar cells. The technique employs spectrally and spatially resolved absorptivity at sub-bandgap wavelengths of perovskite materials, extracted from their luminescence spectra. Parasitic absorption in other layers, carrier diffusion, and photon smearing phenomena are all demonstrated to have negligible effects on the extracted absorptivity. The absorptivity is demonstrated to reflect real degradation in the perovskite film and is much more robust and sensitive than its luminescence spectral peak position, representing its optical bandgap, and intensity. The technique is applied to study various common factors which induce and accelerate degradation in perovskite solar cells including air and heat exposure and light soaking. Finally, the technique is employed to extract the individual absorptivity component from the perovskite layer in a monolithic perovskite/silicon tandem structure. The results demonstrate the value of this approach for monitoring degradation mechanisms in perovskite and perovskite/silicon tandem cells at early stages of degradation and various fabrication stages.
关键词： tandem,absorptivity,photoluminescence,perovskite,degradation
更新于2025-09-12 10:27:22
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Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation
摘要： The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 μm, 10.6 μm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650°C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.
关键词： energy coupling efficiency,absorptivity,high temperatures,surface oxidation,laser material processing
更新于2025-09-11 14:15:04