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2021, iScience
Unusual condensation dynamics occur on the hierarchical Black Silicon metasurface Near-zero water removal time and good water yield are simultaneously achieved Great scalability and multifunctionality are accessible to the proposed water panel
Nanoscale Research Letters, 2016
Although black silicon is used widely as an antireflection coating in solar cells, the corresponding electrical properties are usually poor because the accompanied enlarged surface area can result in increased recombination. Moreover, the high aspect ratio of fragile nanostructured black silicon makes conformal passivation even more challenging. Micropillars are promising alternative candidates for efficiently collecting carriers because the diffusion distance for minority carriers to reach the p-n junction can be shortened; however, the pillar diameter is usually larger than the wavelength of light, inherently increasing the surface reflection. In this paper, we report an approach for decreasing the surface reflection of black silicon and micropillar structures: combining them together to create a dual-scale superstructure that improves the electrical and optical properties concurrently. The reflection of the micropillars decreased significantly as the surface was decorated with a thin black silicon layer, and the thickness of black silicon required for low reflection was reduced as the black silicon was positioned atop micropillars. Three-dimensional finite difference time domain simulations supported these results. Moreover, with such a thin decoration layer, the superstructure displayed improved power conversion efficiency after silicon nitride passivation, suggesting great potential for such superstructures when applied in solar cells.
ACS Applied Nano Materials
Active cooling-based atmospheric water generators, despite their growing demand, continue to be energy intensive and offer poor collection efficiencies (energy consumption per liter of water production). Despite progress in micro-/ nanofabrication techniques and functional coatings, advanced surfaces have not been successfully scaled onto such harvesters to accelerate condensation and improve their efficiencies. Here, we present a scalable dualnanostructured hierarchical surface that comprises sporadically distributed bundles of randomly oriented faceted microcones having facets composed of nanostructures, which are either bumps or ridges. Condensate removal on this surface occurs via drop-to-film coalescence, followed by film shedding in the form of macrodrops. Compared to a conventional plain metal surface used for condensation, the improvement in latent heat transfer coefficient using a hierarchically textured surface ranged from 19.9% at a subcooling of ∼8°C to 1048.4% at a subcooling of ∼1°C in laboratory scale experiments, subcooling being defined with respect to the dew point. To demonstrate utility at industrial scale and to ensure scalability of the modified surfaces, we create a prototype assembly comprising a tube-fin heat exchanger with hierarchically textured fins, cooled using a standard refrigeration cycle, producing ∼25 L of water per day. The prototype containing hierarchically textured fins provides ∼10.8% enhanced water collection at ∼10.4% improved average collection efficiency compared to the traditional water generator when tested in outdoor conditions.
2008 58th Electronic Components and Technology Conference, 2008
Creation of superhydrophobic self-cleaning surfaces is an important objective for a variety of applications. Indeed, numerous routes to generate superhydrophobic surfaces have been proposed. In this paper, a facile way of forming superhydrophobic surfaces is reported that uses Au assisted HF/H 2 O 2 etching of silicon wafers. The Au layer was deposited onto a silicon wafer via e-Beam evaporation. By controlling the evaporation and etching times, the surface roughness can be manipulated and superhydrophobic surfaces with different optical properties can be generated. The effect of etchant concentration on superhydrophobicity was investigated by altering surface structures. Contact angles were measured with a CCD camera equipped goniometer; these values determined the water repellency. Light reflection on the as prepared black surfaces was measured to assess the efficiency for low cost solar cell applications. This approach offers a new way both to theoretically study the surface roughness effect and to investigate engineering applications of self-cleaning surfaces in solar cells, MEMS, anti-bacteria coating, and microfluidic devices.
2017
In this paper, we report an easy and relatively cost effective fabrication technique of a wide band omnidirectional antireflective black silicon surface based on silicon nanowires (SiNWs). An effective and economical one step silver electroless catalytic etching method in an aqueous solution of AgNO3 and HF is used for the synthesis of the black silicon surface. The formation mechanism for SiNW arrays is explained in terms of a localized nanoelectrochemical cell. The length and diameter of the nanowires were controllable as we found a commensurate relationship between dimensions and the etching time. Different sample sizes were used to prove the technique's large scale production potential. Wide range near zero reflection is reported in the visible region due to the strong trapping and antireflective properties in addition to a wide angle up to 60 . Raman scattering measurements confirmed the quantum size effect and phonon scattering in the fabricated structure with different di...
Energy Environ. Sci., 2014
Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al 2 O 3 . Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications.
Nature Nanotechnology, 2015
The nanostructuring of silicon surfaces-known as black silicon-is a promising approach to eliminate front-surface reflection in photovoltaic devices without the need for a conventional antireflection coating. This might lead to both an increase in efficiency and a reduction in the manufacturing costs of solar cells. However, all previous attempts of integrating black silicon into solar cells have resulted in cell efficiencies much below 20% due to the increased charge carrier recombination at the nanostructured surface. Here we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing chemical and electrical passivation. We demonstrate that efficiencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have a real potential to industrial production. Furthermore, we show that use of black silicon can result in 3% increase in the daily energy production when compared to a reference cell with the same efficiency, due to its better angular acceptance.
2016
This work presents an experimental study on the atmospheric water condensation on micro-grooved substrates. The influence of several physical and geometric parameters (relative humidity, substrate inclination with horizontal, groove size) on the process of condensation and drainage is presented. The process is studied by weighing collected water and visualizing the drops formed on the substrate. The grooves appear to markedly increase the collected amount of water by promoting drop coalescence and lowering pinning forces, resulting in early shedding when compared to a smooth surface with same wetting properties.
ACS Applied Materials & Interfaces, 2016
Macroporous layers are grown onto n-type silicon by successive photoelectrochemical etching in HF containing solution and chemical etching in KOH. This specific latter treatment gives highly antireflective properties of the Si surface. The duration of the chemical etching is optimized to render the surface as absorbent as possible and the morphology of the as-grown layer is characterized by scanning electron microscopy. Further functionalization of such structured Si surface is carried out by atomic layer deposition of a thin conformal and homogenous TiO 2 layer that is crystallized by an annealing at 450°C. This process allows using such surfaces as photoanodes for water oxidation. The 40 nm-thick TiO 2 film acts 2 indeed as an efficient protective layer against the photocorrosion of the porous Si in KOH, enhances its wettability and enlarge the light absorption of the photoelectrode. The macroporous Si has a beneficial effect on water oxidation in 1 M KOH and leads to a considerable negative shift of onset potential of ~400 mV as well as a 50 % increase in photocurrent at 1 V vs SCE.
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2021, 2021
Interest in blue energy harvesting systems is rapidly growing and becoming widespread given its promise as a renewable and clean energy source. Blue energy harvesting from raindrop impact would allow lowpower systems to operate in remote areas without the need for battery replacement and related maintenance. Insufficient power output is the most critical limitation that makes the conventional types of rain energy harvester (REH) typically unusable or/and infeasible. To overcome this limitation, a bioinspired metasurface skin is proposed in this paper to serve as the membrane for a piezoelectric type of REHs. The proposed metasurface membrane is comprised of a system of biaxial-cuts inspired by snake scale. The power enhancement of the bio-inspired harvester with a metamembrane was studied and compared to its equivalent conventional harvester with a plain membrane when the substrate was under raindrop pressure. The Finite Element Model (FEM) results showed that the metamembrane could transfer more stress deformation to the piezo-element layer, thus enhancing power output. This is attributable to the metasurface membrane polarizing the PVDF better than a conventional plain membrane because of its higher ability to stretch the PVDF. The proposed bio-inspired harvester could be used for different public facilities such as tents, umbrellas, awnings, temporary roofs, coverings, and tarps to provide power for sensing, lighting, signage, digital displays, etc., especially in heavy-rain regions.
Science advances, 2017
Dewetting is a ubiquitous phenomenon in nature; many different thin films of organic and inorganic substances (such as liquids, polymers, metals, and semiconductors) share this shape instability driven by surface tension and mass transport. Via templated solid-state dewetting, we frame complex nanoarchitectures of monocrystalline silicon on insulator with unprecedented precision and reproducibility over large scales. Phase-field simulations reveal the dominant role of surface diffusion as a driving force for dewetting and provide a predictive tool to further engineer this hybrid top-down/bottom-up self-assembly method. Our results demonstrate that patches of thin monocrystalline films of metals and semiconductors share the same dewetting dynamics. We also prove the potential of our method by fabricating nanotransfer molding of metal oxide xerogels on silicon and glass substrates. This method allows the novel possibility of transferring these Si-based patterns on different materials,...
RSC Adv.
In this paper, we report an easy and relatively cost effective fabrication technique of a wide band omnidirectional antireflective black silicon surface based on silicon nanowires (SiNWs).
International Journal of Heat and Mass Transfer, 2022
Dew formation is due to the radiative cooling of a surface. Surface emissivity is classically considered without the contribution of water condensation. However the latter, with an emissivity of w =0.98, can occupy more than 80% of the surface and strongly affect is radiative properties. Here we present experimental and theoretical studies of the effective surface emissivity, taking into account the presence of the condensing water. The main results are concerned with the effect of the dry surface emissivity on condensation. On the one hand it appears that there is a significant difference between high and low emissivity substrates in the duration of a transient regime at the begining of condensation, making the overall condensation yield smaller for low emissivity substrates. On the other hand, in permanent regime of condensation, the effective surface emissivity is dominated by the presence of drops and the condensation only weakly depends on the dry surface emissivity. These results are of practical importance and can be extended to all application involving radiative heat transfer with condensation.
Applied Surface Science, 2019
18.78% efficiency of crystalline silicon (Si) solar cells was achieved through introducing the combined nanopore/pyramid textures. These hierarchical structures possessed the ultra-low reflectivity with values less than 6% under the various illumination angles from 0 to 60 degree, evidencing their remarkable omnidirectional light-trapping capability. Although the greatly improved light-trapping effect of the hierarchical structures was demonstrated, we found that the increased formation durations of Si nanopores led the substantial increase of photoluminescent characteristics that could limit the efficient separation of photogenerated carriers through charge recombination. Moreover, the positive correlation in surface roughness of nanopore arrays with respect to the elongated etching durations was evidenced, and these issues could increase the series resistance of solar cells owing to poor interfacial contact between nanopores and front electrodes. Thus, there existed the optimal combination between two-scale textures critically for both photonic and electrical
Applied Physics A, 2014
Metasurfaces have been receiving increasing interest due to the complex array of radiation controlling properties that are possible with single-layer films. This talk and work will focus on metasurfaces that can provide light filtering according to wavelength, polarization, and other properties of an incident beam, and applied to a variety of sensors. Also, metasurfaces that exhibit light trapping and localization that can be used for energy generation will be described. One last group of metasurfaces will be discussed that display complex dispersion curves that exhibit fast-and slow-light properties that can be used to study the complex electromagnetic phenomena.
Solar Energy Materials and Solar Cells
Optical losses at the front surface of a silicon solar cell have a significant impact on efficiency, and as such, efforts to reduce reflection are necessary. In this work, a method to fabricate and passivate nanowire-pyramid hybrid structures formed on a silicon surface via wet chemical processing is presented. These high surface area structures can be utilised on the front surface of back contact silicon solar cells to maximise light absorption therein. Hemispherical reflectivity under varying incident angles is measured to study the optical enhancement conferred by these structures. The significant reduction in reflectivity (<2%) under low incident angles is maintained at high angles by the hybrid textured surface compared to surfaces textured with nanowires or pyramids alone. Finite Difference Time Domain simulations of these dual micro-nanoscale surfaces under varying angles supports the experimental results. In order to translate the optical benefit of these high surface area structures into improvements in device efficiency, they must also be well passivated. To this end, atomic layer deposition of alumina is used to reduce surface recombination velocities of these ultra-black silicon surfaces to below 30 cm/s. A decomposition of the passivation components is performed using capacitance-voltage and Kelvin Probe measurements. Finally, device simulations show power conversion efficiencies exceeding 21% are possible when using these ultra-black Si surfaces for the front surface of back contact silicon solar cells.
Nature Communications, 2018
Water scarcity is a particularly severe challenge in arid and desert climates. While a substantial amount of water is present in the form of vapour in the atmosphere, harvesting this water by state-of-the-art dewing technology can be extremely energy intensive and impractical, particularly when the relative humidity (RH) is low (i.e., below~40% RH). In contrast, atmospheric water generators that utilise sorbents enable capture of vapour at low RH conditions and can be driven by the abundant source of solar-thermal energy with higher efficiency. Here, we demonstrate an air-cooled sorbent-based atmospheric water harvesting device using the metal−organic framework (MOF)-801 [Zr 6 O 4 (OH) 4 (fumarate) 6 ] operating in an exceptionally arid climate (10-40% RH) and sub-zero dew points (Tempe, Arizona, USA) with a thermal efficiency (solar input to water conversion) of~14%. We predict that this device delivered over 0.25 L of water per kg of MOF for a single daily cycle.
Scientific reports, 2015
This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design ...
2024
Solar-driven interfacial evaporation (SIE) is an emerging research topic that is gaining attention due to its potential in addressing global water scarcity issues. This review provides a comprehensive overview of base materials, recent innovations in photothermal materials and the design of evaporators for effective water desalination and purification. The recent development of SIE is meticulously discussed, providing a deep understanding of the key performance indicators and state-of-the-art materials. Additionally, this review examines novel strategies that have been reported in the literature for enhancing the efficiency and scalability of SIE systems. These strategies involve using photothermal materials and exploring innovative device configurations. Finally, we discuss the existing challenges and future research directions, emphasizing the potential of SIE in addressing global water scarcity and contributing to a sustainable future.
Nanoscale, 2017
Efforts to realize thin-film solar cells on unconventional substrates face several obstacles in achieving good energy-conversion efficiency and integrating light-management into the solar cell design. In this report a technique to circumvent these obstacles is presented: transferability and an efficient light-harvesting scheme are combined for thin-film silicon solar cells by the incorporation of a NaCl layer. Amorphous silicon solar cells in p-i-n configuration are fabricated on reusable glass substrates coated with an interlayer of NaCl. Subsequently, the solar cells are detached from the substrate by dissolution of the sacrificial NaCl layer in water and then transferred onto a plastic sheet, with a resultant post-transfer efficiency of 9%. The light-trapping effect of the surface nanotextures originating from the NaCl layer on the overlying solar cell is studied theoretically and experimentally. The enhanced light absorption in the solar cells on NaCl-coated substrates leads to ...
2012
In Thin Film Silicon (TF-Si) solar cells light harvesting schemes must guarantee an efficient light trapping in the thin absorber layers without decreasing the silicon layers quality and consecutively the p-in diodes electrical performance. TF-Si solar cells resilience to the substrate roughness is reported to be possibly improved through optimizations of the cell design and of the silicon deposition processes. By further tailoring the superstrate texture, amorphous silicon / microcrystalline silicon (a-Si:H/µc-Si:H) tandem solar cells with an initial efficiency up to 13.7 % and a stabilized efficiency up to 11.8 % are demonstrated on single-scale textured superstrates. An alternative approach combining large and smooth features nanoimprinted onto a transparent lacquer with small and sharp textures from asgrown LPCVD ZnO is then shown to have a high potential for further increasing TF-Si devices efficiency. First results demonstrate up to 14.1 % initial efficiency for a TF-Si tandem solar cell.
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