Wavelengths Of Solar Spectrum Research Articles

Performance evaluation of a porous polymer-nickel foam compound cooler combining radiative and evaporative cooling

The radiative cooling technology and evaporative cooling technology have drawn intense attentions due to zero energy consumption and negligible carbon footprint, and the afflatus to combine the above two passive cooling technologies has been strongly inspired. The compound cooling mode combining radiative cooling and evaporative cooling can theoretically break through the application limitations under the harsh environmental conditions, but the specific cooling performance needs to be further investigated in conjunction with actual environmental conditions. Herein, a porous polymer-nickel foam (PP-NF) compound cooler is fabricated. The upper porous polymer radiative coating (PPRC) is the radiative cooling layer, and the emissivity is as high as 97% within the atmospheric window (8–13 μm), while the reflectivity is about 98% and 94% in the visible wavelength range (0.38–0.78 μm) and the solar spectrum wavelength range (0.25–2.5 μm), demonstrating remarkable radiative cooling capability. The bottom nickel foam filled with anhydrous calcium chloride (CaCl2) is the evaporative cooling layer, which can absorb water in nighttime to meet the needs of efficient evaporative cooling in daytime. The comprehensive properties of the PP-NF cooler are very impressive for cooling applications, and the outdoor experimental and theoretical results show that the temperature drop and cooling power of the PP-NF cooler can reach 2.7 °C (12:00–13:00) and 100.30 W/m2 (12:00–16:00), which are increased by 42.1% and 24.7% compared to the PPRC cooler with radiative cooling only. Furthermore, the cooling performance of the PP-NF cooler is better than the evaporative cooler in high humidity environment with the relative ambient humidity exceeding 63% through the quantitative analysis of experimental and related theoretical results. The PP-NF cooler has a bright application prospect, and it is very likely to play an indispensable role in the improvement and optimization of the energy framework in the foreseeable future.

Comparison of Soil Moisture Content Retrieval Models Utilizing Hyperspectral Goniometer Data and Hyperspectral Imagery From an Unmanned Aerial System

AbstractTo understand surface biogeophysical processes, accurately evaluating the geographical and temporal fluctuations of soil moisture is crucial. It is well known that the surface soil moisture content (SMC) affects soil reflectance at all solar spectrum wavelengths. Therefore, future satellite missions, such as the NASA Surface Biology and Geology mission, will be essential for mapping and monitoring global soil moisture changes. Our study compares two widely used moisture retrieval models: the multilayer radiative transfer model of soil reflectance (MARMIT) and the soil water parametric (SWAP)‐Hapke model. We evaluated the SMC retrieval accuracy of these models using unmanned aerial systems (UAS) hyperspectral imagery and goniometer hyperspectral data. Laboratory analysis employed hyperspectral goniometer data of sediment samples from four locations reflecting diverse environments, while field validation used hyperspectral UAS imaging and coordinated ground truth collected in 2018 and 2019 from a barrier island beach at the Virginia Coast Reserve Long‐Term Ecological Research site. The (SWAP)‐Hapke model achieves comparable accuracy to MARMIT using laboratory hyperspectral data but is less accurate when applied to UAS hyperspectral imagery than the MARMIT model. We proposed a modified version of the (SWAP)‐Hapke model, which achieves better results than MARMIT when applied to laboratory spectral measurements; however, MARMIT's performance is still more accurate when applied to UAS imagery. These results are likely due to differences in the models' descriptions of multiply‐scattered light and MARMIT's more detailed description of air‐water interactions.

Super-hydrophobic graphene-coated thermoplastic polyurethane porous monolith with superior photothermal effect for solar-assisted efficient cleanup of crude oil spill

Frequent occurrences of oil spill accidents have posed a serious threat to ecological system and human health, hence it is imperative to explore new-typed absorbent materials to efficiently clean up high-viscosity crude oil in an environmentally-friendly way. Herein we reported a reduced graphene oxide-wrapped and fluoroalkylsilane-modified thermoplastic polyurethane porous monolith (abbr. F-rGO@TPU monolith) with superior photothermal effect for solar-driven high-efficiency cleanup of crude oil spill. Owing to superior superhydrophobicity (water contact angle of 153°) and porosity (87.4 %), the as-prepared F-rGO@TPU monolith possessed high saturated absorption capacity (6.5–53.7 g/g) and splendid oil/water separation efficiency (over 99.3 %) for various low-viscosity oils/organic solvents. Excellent reversible compressibility and fatigue resistance (1000 compression cycles under 80 % strain) allowed the monolith to repetitively absorb oil via simple manual squeezing. By virtue of the outstanding photothermal effect of reduced graphene oxide coating, the F-rGO@TPU monolith exhibited almost full absorption (96.0 %) of solar spectrum (wavelength range of 250–2500 nm) and efficient light-to-heat conversion capability (achieving 80 °C in 5 min under 1.0 kW/m2 solar irradiation), enabling it to in situ reduce the viscosity of crude oil for rapid absorption. More importantly, the solar-heated monolith could continuously and fast separate crude oil/water mixture by a pump-assisted absorption device (crude oil flux of 510 kg/(m2·h)), revealing immense potential in oil spill remediation.

Investigations on the Influence of Surface Textures on Optical Reflectance of Multi-crystalline Silicone (MC-Si) Crystal Surfaces-Simulations and Experiments

MC-Si is the most widely used material for making solar PV cells. In spite of the considerable research on improving the conversion efficiency of MC-Si solar PV cells still it remains well within the range of 15-20%. Optical reflectance being the major loss of incident solar energy, efforts are being made to reduce the optical reflectance of solar cell surfaces. Among the several methods proposed, creation of well-defined surface topography on the cell surface remains a promising option. Micro/nano level features with various dimensions and distributions have been created on MC-Si crystal surfaces using a femto-second pulsed laser and the influence of surface topography on optical reflectance in the incident light wave length of 350 – 1000 nm have been studied and compared with the simulation results obtained using OPAL2 software. Experimental results indicate that surface textures on the wafer surface lead to the reduction of optical reflectance in the range of 20-35% in comparison with plain surface. Width of micro grooves have less significant effect on the optical reflectance in comparison with pitch between the micro grooves. Best reduction in reflectance is exhibited by the texture having a groove width of 30 mm and a pitch of 100 mm. A post texturing etching operation is found to have detrimental effect on the ability of micro/nano level features in decreasing the optical reflectance in the preferred wavelength of solar spectrum due to the flattening of nano level features created within the micro grooves due to laser texturing.

High-Entropy-Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion.

Photothermal materials with broadband optical absorption and high conversion efficiency are intensively pursued to date. Here, proposing by the d-d interband transitions, we report an unprecedented high-entropy alloy FeCoNiTiVCrCu nanoparticles that the energy regions below and above the Fermi level (±4 eV) have been fully filled by the 3d transition metals, which realizes an average absorbance greater than 96 % in the entire solar spectrum (wavelength of 250 to 2500 nm). Furthermore, we also calculated the photothermal conversion efficiency and the evaporation rate towards the steam generation. Due to its pronounced full light capture and ultrafast local heating, our high-entropy-alloy nanoparticle-based solar steam generator has over 98 % efficiency under one sun irradiation, meanwhile enabling a high evaporation rate of 2.26 kg m-2 h-1 .

High‐Entropy‐Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion

AbstractPhotothermal materials with broadband optical absorption and high conversion efficiency are intensively pursued to date. Here, proposing by the d‐d interband transitions, we report an unprecedented high‐entropy alloy FeCoNiTiVCrCu nanoparticles that the energy regions below and above the Fermi level (±4 eV) have been fully filled by the 3d transition metals, which realizes an average absorbance greater than 96 % in the entire solar spectrum (wavelength of 250 to 2500 nm). Furthermore, we also calculated the photothermal conversion efficiency and the evaporation rate towards the steam generation. Due to its pronounced full light capture and ultrafast local heating, our high‐entropy‐alloy nanoparticle‐based solar steam generator has over 98 % efficiency under one sun irradiation, meanwhile enabling a high evaporation rate of 2.26 kg m−2 h−1.

Significant zinc release from widely-used commercial lithopone pigments under solar irradiation

Lithopone pigments are an important group of white inorganic pigments, with production exceeding 240,000 tons/year in China. Nevertheless, our understanding of its environmental behavior is still limited. In this work, we reported the fast and extensive release of Zn2+ from the commercial lithopone pigment under solar exposure. The lithopone pigment released 40.97% of its total Zn within 24-h simulated sunlight exposure, generating a significant amount of nanoparticles. The commercial lithopone pigment had bandgap energy of 3.63 eV. It can be excited within the solar spectrum (wavelength <342 nm). As suggested by the photocurrent and surface photovoltage results, the pigment generated electrons and holes with good separation and transfer efficiency upon solar irradiation. The pigment also produced hydroxyl radical and superoxide by the oxidation of surface-bound OH− and H2O by the holes and direct transfer of the electrons to oxygen molecules. The photogenerated holes can oxidize the pigment, leading to its photo-dissolution and consequently the release of Zn2+. The water chemistry, including pH, coexisting anions, and organic carbons, influenced the photo-dissolution kinetics of the pigment by changing the valence band edge, forming stable precipitates, competing for the holes, and screening effect. The release of Zn2+ from the commercial lithopone pigment was fast and extensive under natural conditions, with 35.16% Zn released within 6-h solar exposure. Our results highlighted the crucial role of photochemistry in the environmental risk assessments and regulations of commercial lithopone pigments.

Full Solar-Spectrum Power-Generation System Based on High Efficiency and Wide Spectral Splitter Film and Fresnel Lens

Based on high efficiency and wide spectral splitter film and Fresnel lens, we have theoretically investigated a full solar-spectrum power-generation system. Designed nano-multilayers are fabricated on Fresnel lens. Then short wavelengths (400 nm ~ 1100 nm) of solar-spectrum can be transmitted 95% to the solar cell, and long wavelengths (1100 nm ~ 2500 nm) of solar-spectrum can be reflected 90% and focused to the thermoelectric cell. This system can combine the efficiency of solar cells and thermoelectric cells to generate electricity across the entire solar spectrum. In theory, the limit for total conversion efficiency is $\eta =56.64$ %.

Thermal and cost analysis of various air filled double glazed reflective windows for energy efficient buildings

The enormous amount of energy is being consumed by buildings in an attempt to deliver thermal comfort in buildings. This paper aims at reducing/increasing the total solar heat gain through various combinations of double glazed reflective windows of buildings. The spectral characteristics of six reflective glasses namely bronze, green, grey, opal blue, sapphire blue and gold-reflective glasses at a normal angle of incidence by using UV-3600 Shimadzu spectrophotometer according to ASTM E 424 standards were experimentally measured. The solar optical properties of the glasses were deduced by developing a MATLAB code using spectral data which was obtained from experiments in the solar spectrum wavelength range of 300 nm–2500 nm. Thirty air-filled double-glazed reflective windows have been studied for both thermal and cost analysis in the Indian composite climatic zone (New Delhi 28.580 N, 77.200 E). The configuration C13 (Grey reflective glass-Air gap 10 mm-Gold reflective glass) is observed to be the best air-filled double glazed window from the highest annual cost savings ($ 79.29 per annum in SE direction) and lower payback period (1.42 years) point of views among thirty double-glazed reflective glasses studied. The results of this paper are useful in the design of sustainable passive solar buildings.

Enhancement of light trapping for thin film solar cells

ABSTRACTLight trapping is one of the key challenges for next generation thin film solar cells. In this work, we have identified the distinct light trapping effects for short and long wavelength solar spectrum range, by investigating lighting trapping structures on both sides of Si thin film solar cells. The sub-wavelength photonic front surface by wet etching and multi-layer photonic crystal reflector on the bottom surface are studied in detail for its solar energy absorption characteristics. Our study reveals the drastic difference of the light trapping effects within the solar spectrum wavelength. This work may provide guidance for the efficiency enhancementfor next generation thin film photovoltaic cells.

Structural SPR Tunability of Metal@Graphene Core–Shell Nano-Needle and Nano-Disk

In present paper, a design of the graphene-coated metal (Ag/Au/Cu) nano-disk (2D) and nano-needle (1D) has been studied within the quasi-static approximation. The core@shell nano-geometries display dual dipolar plasmonic resonances which can be influenced by the resonance coupling between the plasmonic modes of the core and shell. These results indicate two different types of plasmon coupling and their wide range of SPR tunabilty: one is symmetric (1100~1600 nm) and other is anti-symmetric coupling (700~1120 nm). The resonance tunability in the symmetric and the anti-symmetric modes are strongly dependent on the sizes of the metallic core (semi major axes of the core 16~24 nm), graphene mono layer (GML) shell thickness (0.01~0.05 nm), and the ASR (0.06~0.12) of the core@shell nano-structure. Metal@GML nano-geometries are embedded in organic environment of the two different polymer matrices PCDTBT:PC71BM (em=3.36) and PTB7:PC71BM (em=3.47) that show an appropriate SPR tunability instead of non-coated metallic nano-disk and nano-needle. We have analyzed optical properties of coated and non-coated nano-geometries in terms of SPR tunability and extinction efficiency (Qext). For a fixed ASR, the symmetric modes of nano-disks have a wide range of SPR tunability in the IR range, while for nano-needles, both the modes having wide range of tunability in visible to IR region. Similarly for a fix TGML, the symmetric modes of nano-needles have a high tunability in the IR region. Hence, both the nano-geometries having a great potential for light trapping in the desirable range of wavelength of solar spectrum.

Analyzing p-type Conjugated Conducting Poly (diaminonaphthalene) Doped Poly (vinyl alcohol) Bulk Hetrojunction Film for Organic Solar Cells

Bulk Hetrojunction configuration for those electronics devices which require interpenetrating strength with large doner-acepter interfacial area is the matter of concern in microelectronics. At the same time developing p-type conjugated conducting polymers with easy synthesis, high charge carrier mobility, strong absorption properties and suitable energy gap for bulk hetrojunction (BHJ) are also required for sake of efficient applications. BHJ solar cell architecture, where in bulk, phase separation between the two components are required in controlled form are achieved by both accepter and donor materials which enhance the solar cell performance in terms of parameters like power conversion efficiency and fill factor. Poly (diaminonaphthalene) doped Poly (vinyl alcohol) (PDAN doped PVA), a p-type conjugated conducting polymer film, may be the materials for bulk semiconductor hetrostructure. The D.C conductivity at room temperature of PDAN doped PVA film was found to be 2.0408 x 10-4 mho m-1 which gives the mobility in the range of 0.43 cm2/Vs. The economic chemical oxidation method was used for synthesizing PDAN doped PVA films. The Arrhenius plot provides the energy band gap of the order of 1.312 eV which is smaller than the limit 1.77 eV for approximately 700 nm range wavelength of solar spectrum for photovoltaic mechanism. The spatial parameter “redundance” calculated from Atomic Force Microscopy (AFM) which provides the fractal morphology of the sample, was found to be -0.18 for PDAN doped PVA film thus suggests for less disordered surface which satisfies the desired criteria for electronics applications.

Imaging the Anomalous Charge Distribution Inside CsPbBr3 Perovskite Quantum Dots Sensitized Solar Cells.

Highly luminescent CsPbBr3 perovskite quantum dots (QDs) have gained huge attention in research due to their various applications in optoelectronics, including as a light absorber in photovoltaic solar cells. To improve the performances of such devices, it requires a deeper knowledge on the charge transport dynamics inside the solar cell, which are related to its power-conversion efficiency. Here, we report the successful fabrication of an all-inorganic CsPbBr3 perovskite QD sensitized solar cell and the imaging of anomalous electrical potential distribution across the layers of the cell under different illuminations using Kelvin probe force microscopy. Carrier generation, separation, and transport capacity inside the cells are dependent on the light illumination. Large differences in surface potential between electron and hole transport layers with unbalanced carrier separation at the junction have been observed under white light (full solar spectrum) illumination. However, under monochromatic light (single wavelength of solar spectrum) illumination, poor charge transport occurred across the junction as a consequence of less difference in surface potential between the active layers. The outcome of this study provides a clear idea on the carrier dynamic processes inside the cells and corresponding surface potential across the layers under the illumination of different wavelengths of light to understand the functioning of the solar cells and ultimately for the improvement of their photovoltaic performances.

Embedded Metal Electrode for Organic-Inorganic Hybrid Nanowire Solar Cells.

We demonstrate here an embedded metal electrode for highly efficient organic-inorganic hybrid nanowire solar cells. The electrode proposed here is an effective alternative to the conventional bus and finger electrode which leads to a localized short circuit at a direct Si/metal contact and has a poor collection efficiency due to a nonoptimized electrode design. In our design, a Ag/SiO2 electrode is embedded into a Si substrate while being positioned between Si nanowire arrays underneath poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), facilitating suppressed recombination at the Si/Ag interface and notable improvements in the fabrication reproducibility. With an optimized microgrid electrode, our 1 cm2 hybrid solar cells exhibit a power conversion efficiency of up to 16.1% with an open-circuit voltage of 607 mV and a short circuit current density of 34.0 mA/cm2. This power conversion efficiency is more than twice as high as that of solar cells using a conventional electrode (8.0%). The microgrid electrode significantly minimizes the optical and electrical losses. This reproducibly yields a superior quantum efficiency of 99% at the main solar spectrum wavelength of 600 nm. In particular, our solar cells exhibit a significant increase in the fill factor of 78.3% compared to that of a conventional electrode (61.4%); this is because of the drastic reduction in the metal/contact resistance of the 1 μm-thick Ag electrode. Hence, the use of our embedded microgrid electrode in the construction of an ideal carrier collection path presents an opportunity in the development of highly efficient organic-inorganic hybrid solar cells.

Solar Irradiance from 165 to 400 nm in 2008 and UV Variations in Three Spectral Bands During Solar Cycle 24

Accurate measurements of the solar spectral irradiance (SSI) and its temporal variations are of primary interest to better understand solar mechanisms, and the links between solar variability and Earth’s atmosphere and climate. The SOLar SPECtrum (SOLSPEC) instrument of the Solar Monitoring Observatory (SOLAR) payload onboard the International Space Station (ISS) has been built to carry out SSI measurements from 165 to 3088 nm. We focus here on the ultraviolet (UV) part of the measured solar spectrum (wavelengths less than 400 nm) because the UV part is potentially important for understanding the solar forcing of Earth’s atmosphere and climate. We present here SOLAR/SOLSPEC UV data obtained since 2008, and their variations in three spectral bands during Solar Cycle 24. They are compared with previously reported UV measurements and model reconstructions, and differences are discussed.

Optical Confinements in Correlated Spectral Characteristics of Vertically Aligned Silicon Nanometric Wires Followed by a Facile Fabrication Thereof

Nanometric wires, in particular, vertically aligned silicon nanowires, possess a huge prospect in current thin film solar cell technologies. A bottom-up process to acquire vertically aligned silicon nanowire (Si-NW) on c-Si wafer was demonstrated and characterized. A well coverage of Si-NWs on c-Si, ca. 6.5 × 108/cm2, was obtained. SEM micrograph confirmed a variation in Si-NW size in length as well as in diameter. On the other hand, inherent optical characteristics of nanometric wires define the performance of such nanowire-based thin film solar cell. Therefore, key factors, such as absorption profile, energy flow, electromagnetic (EM) field, and generation rate distribution in typical model, “Si-NW on c-Si slab,” have been observed at different wavelengths of solar spectrum. A single Si-NW of cylindrical shape was modelled on c-Si and optimized to elucidate the aforementioned characteristics. Light absorption at 700 nm was found to be the best in this scenario, and therefore, EM field and Poynting vector distribution were simulated at the same wavelength. It was revealed that at 700 nm, strongest sites of EM field and energy flow became more available and confined. Exciton generation rate was found to be distributed and confined all the way down to the bottom of the wire. A correlated phenomenon such as optical confinements in spectral characteristics in nanoscale is elucidated. Such a focused prediction in spectral optical characteristics and facile fabrication route is indispensable in optoelectronics as well as nanowire-based advanced electronic design.

Optical properties and thermal stability of La1−xSrxCoO3−δ (0.2 ⩽ x ⩽ 0.8) ceramics

Perovskite-type La1−xSrxCoO3−δ (0.2⩽x⩽0.8) ceramics were prepared by tape casting and solid state reaction method. The room temperature optical properties of these samples were studied in detail. The temperature dependent emittance measurements and high-temperature durability tests were carried out. Results showed that these materials exhibited low reflectance at the solar spectrum wavelengths and high reflectance in the infrared region, with an optimal spectral selectivity of 3.2. The investigated samples showed low thermal emittance at high temperatures. More importantly, the sample was highly stable in air at 800°C, as the performance criterion value was lower than 0.05 after 10 cycles (90h) heat treatment. Our results demonstrate that the La1−xSrxCoO3−δ ceramics have the potential to emerge as high temperature (∼800°C) solar absorbers for the future solar power systems.

Wireless InGaN–Si/Pt device for photo-electrochemical water splitting

We demonstrate a wireless device comprising a gallium nitride (GaN)–silicon-based photo-electrode, and a platinum cathode. Compared with conventional two-electrode photo-electrochemical systems, this wireless monolithic device showed potential for a wider range of applications, and reduced the resistance losses resulting from the wiring and aqueous solution. The efficiency was improved when the electrolyte was changed from KHCO3 to NaOH because water oxidation capability of the surface of the GaN was enhanced. A wider solar spectrum wavelength range was exploited by adopting InGaN as a photo-absorption layer; the improved efficiency for hydrogen generation was 0.90%.

Potential of ITO nanoparticles formed by hydrogen treatment in PECVD for improved performance of back grid contact crystalline silicon solar cell

This paper discusses the prospect of using indium tin oxide (ITO) nanoparticles as back scatterers in crystalline silicon solar cells instead of commonly used metal nanoparticles as ITO nanoparticles have comparatively low dissipative losses and tunable optical properties. ITO nanoparticles of ∼5–10nm size is developed on the rear side of the solar cell by deposition of ∼5–10nm thick ITO layer by DC magnetron sputtering followed by hydrogen treatment in PECVD. The silicon solar cell is fabricated in the laboratory using conventional method with grid metal contact at the back surface. Various characterizations like FESEM, TEM, AFM, XRD, EQE and IV characteristics are performed to analyze the morphology, chemical composition, optical characteristics and electrical performance of the device. ITO nanoparticles at the back surface of the solar cell significantly enhances the short circuit current, open circuit voltage and efficiency of the solar cell. These enhancements may be attributed to the increased absorption and carrier collection at longer wavelengths of solar spectrum due to enhanced light trapping by the ITO nanoparticles and surface passivation by the hydrogen treatment of the back surface.

Characteristics of a-SiC:H/a-SiGe:H/a-Si:H Thin Film Solar Cells Enhanced by CH4 Flow Rates Controlling in P-Layer

We fabricated a a-SiC:H / a-SiGe:H / a-Si:H thin film solar cell by adjusting CH4 flow rate in order to absorb long wavelength of solar spectrum without stacked structures such as triple junctions. The a-SiC:H, a-SiGe:H and a-Si:H layers with sheet resistance 7∼8 ohm/sq were deposited on indium tin oxide (ITO) glass by 13.56 MHz radical-assisted plasma-enhanced chemical vapor deposition (RA-PECVD). The working pressure and substrate temperature were 750 mTorr and 250°C, respectively. The a-SiC:H films for p-layer thickness of 300 Å were deposited using 10% CH4 diluted in H2. The thickness of a-SiGe:H for i-layer corresponded to 2000 Å. The n-layer was fabricated using 1% PH3 in diluted H2. The optical properties of these films were measured by UV-VIS spectrophotometer. The thickness of the film was estimated by FE-SEM were observation. The various values of Jsc, Voc, FF and conversion efficiency were evaluated by the solar simulator.