Sunlight Research Articles

Analysis of graphene coatings on various metallic/oxide crystal/composite material substrates using machine learning for enhanced solar thermal energy conversion

Because energy interest demands clean and sustainability in the last ten years. Solar thermal energy conversion, where sunlight can be absorbed to convert it into heat can stand as an alternative for this purpose. Graphene dispersed with different substrates enables us to get torsion control over light absorption and heat transport. This work discusses the optothermal properties of graphene-based coatings on different substrates such as CuO, MAPBI3, Fe, etc. The optothermal properties of such CuO-graphene, MAPBI3-graphene, and Fe-graphene combinations display the highest average absorptance of 96.8% across the solar spectrum between 0.2 and 2.5 μm followed by 86.7% by MAPBI3-graphene. However, Fe-graphene depicts a significantly lower value of 24.3%. A critical inspection of these optothermal properties would enrich one with critical knowledge of design optimisation in graphene-coated solar absorbers. Thus, the data collection time is greatly reduced using ML compared to running simulations which have a step size of about 8 h per change. Where the machine learning efficacy is 98% for the thickness optimization of Fe, CuO, and MAPBI3 with 25% test data. Of much potential interest are the solar absorbers developed using these materials in fields such as solar thermal energy harvesting, air/water heaters, and industrial heating systems.

Designing Biomimetic Leaves for Solar Spectrum Similarity and Even Multifunction

Designing Biomimetic Leaves for Solar Spectrum Similarity and Even Multifunction

A dozen predicted SiGe alloys with low enthalpies and strong absorption of sunlight for photovoltaic applications.

Silicon germanium alloy materials have promising potential applications in the optoelectronic and photovoltaic industries due to their good electronic properties. However, due to the inherent brittleness of semiconductor materials, they are prone to rupturing under harsh working environments, such as high stress or high temperature. Here, we conducted a systematic search for silicon germanium alloy structures using a random sampling strategy, in combination with group theory and graph theory (RG2), and 12 stable SiGe structures in 2-8 stacking orders were predicted. All 12 stable SiGe crystals exhibit a popular bandwidth of 1.06-1.19 eV, approaching the optimal Shockley Queisser limit (≈1.4 eV). Among these, 6 structures showed quasi-direct band gaps. Considering their potential photovoltaic applications, we systematically studied the changes in their enthalpy, stability, mechanical stability (elastic moduli), lattice parameters, band structures, and light absorption under a stress load of up to 20 GPa. These new SiGe crystals featured relatively low enthalpies (even as low as 0.009 eV per atom), and good stability and mechanical properties. In addition, the absorption spectra of these materials demonstrated a high absorption intensity for the solar spectrum that was approximately 3 times higher than that of conventional diamond silicon, even under a 20 GPa stress. The present study uses the predicted 2-8H SiGe to provide new insights into the photovoltaic applications of SiGe alloy structures.

Comprehensive Study of Highly efficient Rb2AgInX6 (X = Cl, Br, I) based Lead-Free Double Perovskite Solar Cells

Abstract Lead-free Double Perovskite Solar Cells (DPSCs) have generated great study interest recently as a potential perovskite absorber layer, due to their cost-effectiveness, impressive stability, and superior performance. In this study, we investigated Rb2AgInX6(Cl, Br, I) based DPSCs using SCAPS-1D simulation software. Various properties, such as the density of states for conduction and valance bands, carrier concentration, and carrier mobility (electrons and holes), were calculated for simulation. Furthermore, we have optimized defect density, electron affinity, and thickness of absorber layers for Rb2AgInX6-based DPSCs. We investigated how DPSC parameters were impacted by operating temperature and then performed band gap tuning for Rb2AgInBr6-based DPSC along with their temperature stability. Tandem solar cells (TSC) have had an enormous influence on the field of photovoltaics (PV) because of their ability to effectively use a wider range of solar spectrum and reduce unwanted energy loss. In this context, we have also simulated Rb2AgInBr6/Rb2AgInI6 based an all double perovskite tandem solar cells and optimized the same for future experimental applications. The optimized PCE of 12.14 %, 26.49 %, and 13.95 % were obtained for Rb2AgInX6(X=Cl, Br, I respectively) based DPSCs. In comparison, the PCE of 38.70 % was obtained for tandem structure.

High‐Performance Overall Water Splitting Dominated by Direct Ligand‐to‐Cluster Photoexcitation in Metal–Organic Frameworks

AbstractExpanding the spectral response of photocatalysts to facilitate overall water splitting (OWS) represents an effective approach for improving solar spectrum utilization efficiency. However, the majority of single‐phase photocatalysts designed for OWS primarily respond to the ultraviolet region, which accounts for a small proportion of sunlight. Herein, we present a versatile strategy to achieve broad visible‐light‐responsive OWS photocatalysis dominated by direct ligand‐to‐cluster charge transfer (LCCT) within metal–organic frameworks (MOFs). Three synthesized OWS MOFs, namely Fe2MCbz (M2+ = Mn2+, Co2+, Ni2+), exhibited intrinsic OWS capability without the requirement for extra photosensitizer or sacrificial agent or cocatalyst. Among these, Fe2NiCbz was identified as the superior performer, and when dispersed with polyacrylonitrile nanofibers using electrospinning technology, it achieved the highest OWS rates of 170.2 and 85.1 μmol g−1 h−1 for H2 and O2 evolution, surpassing all previously documented MOF‐based photocatalysts. Experimental and theoretical analyses revealed that direct LCCT played a crucial role in enhancing the photocatalytic efficiency, with exceptional performance of Fe2NiCbz attributed to its well‐optimized energy level structures and highly efficient charge transfer mechanism. This work not only sets a benchmark in OWS MOF photocatalysts but also paves the way for maximizing solar spectrum utilization, thereby advancing renewable hydrogen production strategy.

High-Performance Overall Water Splitting Dominated by Direct Ligand-to-Cluster Photoexcitation in Metal-Organic Frameworks.

Expanding the spectral response of photocatalysts to facilitate overall water splitting (OWS) represents an effective approach for improving solar spectrum utilization efficiency. However, the majority of single-phase photocatalysts designed for OWS primarily respond to the ultraviolet region, which accounts for a small proportion of sunlight. Herein, we present a versatile strategy to achieve broad visible-light-responsive OWS photocatalysis dominated by direct ligand-to-cluster charge transfer (LCCT) within metal-organic frameworks (MOFs). Three synthesized OWS MOFs, namely Fe2MCbz (M2+ = Mn2+, Co2+, Ni2+), exhibited intrinsic OWS capability without the requirement for extra photosensitizer or sacrificial agent or cocatalyst. Among these, Fe2NiCbz was identified as the superior performer, and when dispersed with polyacrylonitrile nanofibers using electrospinning technology, it achieved the highest OWS rates of 170.2 and 85.1 μmol g-1 h-1 for H2 and O2 evolution, surpassing all previously documented MOF-based photocatalysts. Experimental and theoretical analyses revealed that direct LCCT played a crucial role in enhancing the photocatalytic efficiency, with exceptional performance of Fe2NiCbz attributed to its well-optimized energy level structures and highly efficient charge transfer mechanism. This work not only sets a benchmark in OWS MOF photocatalysts but also paves the way for maximizing solar spectrum utilization, thereby advancing renewable hydrogen production strategy.

Sustainable passive radiation cooling transparent film for mobile phone protective screens

Passive daytime radiative cooling (PDRC) is a promising approach to address energy, environmental, and safety issues caused by global warming, with high emissivity in a transparent atmospheric window and high reflectivity in the solar spectrum. However, most demonstrations of PDRC rely mainly on complex and expensive spectral selective nanophotonic structures, requiring specialized photonic structures that are both expensive and difficult to obtain. The superiorities of low-cost, abundant resources, renewability, and high value-added biomass resources prompt Gleditsia sinensis polysaccharides (GSP) to be used in thermal emission materials to explore further the characteristics of regulating object temperature within a specific range without any external energy consumption. The three-layer thermal emission film (PDMS3PG3/t4) obtained by the scalable scraping method has high transparency, hydrophobicity (114.2°), and super flexibility. The spectral variations of non-selective PDMS3PG3/t4 (1.0wt% GSP, 800 μm thickness) in the 3-5μm and 8-13μm waveband ranges were discussed in detail, and high emissivities of 69.1% and 92.2% were obtained, respectively. PDMS3PG3/t4 was appointed a mobile phone screen film and experimented with a 4.9°C average temperature difference below ambient temperature, materializing prime PDRC and desiring to broaden the passive cooling technology and reduce the global energy burden.

Improved absorption of phosphates through interface junctions and photothermal–energy–storage capability of Ca(OH)2–[Co3O4–Co3(PO4)2]

Improved absorption of phosphates through interface junctions and photothermal–energy–storage capability of Ca(OH)2–[Co3O4–Co3(PO4)2]

Backscattering properties of trigonal Ge-Au Janus nanoparticles with different ambient refractive indices in the visible solar spectrum

Backscattering properties of trigonal Ge-Au Janus nanoparticles with different ambient refractive indices in the visible solar spectrum

Recent updates on full solar spectrum metal sulphides photocatalyst for hydrogen peroxide generation: Modification strategies and mechanistic insights

Recent updates on full solar spectrum metal sulphides photocatalyst for hydrogen peroxide generation: Modification strategies and mechanistic insights

Hybrid Nanofluids-Based Direct Absorption Solar Collector: An Experimental Approach

In the last years, studies have demonstrated the potential of hybrid nanofluids to enhance the performance of direct absorption solar collectors. These working fluids containing noble metals (gold, silver) are known for their local surface plasmon resonance which is the main cause for the increased absorption within the solar spectrum. In the current paper, new direct absorption solar collectors prototypes using water-ethylene glycol solution and 0.1 wt.% silver nanoparticles + reduced graphene oxide dispersed in water-ethylene glycol mixture were designed, built, and tested under outdoor conditions, at two flow rates (1.0 and 1.5 l·min−1) and two inlet temperatures (20 ∘C and 30 ∘C), over several days in September 2023, at Brasov, Romania. The results suggested that by using silver nanoparticles + reduced graphene oxide nanofluid, the efficiency is improved related to water-ethylene glycol solution. The maximum relative enhancement in efficiency was 16.72% related to the base fluid. Also, at 1.0 l·min−1, the instantaneous and accumulative energies delivered were about 13.51% and 42.91%, respectively, higher than the water-ethylene glycol solution. Finally, the current results were compared to other research carried out on full-scale direct absorption solar collectors tested in outdoor conditions.

MTiTaO6: Cr3+ (M = Al3+, Ga3+, Sc3+) Phosphors with Ultra‐Broadband Excitation Spectra and Enhanced Near‐Infrared Emission for Solar Cells

AbstractAchieving ultra‐broadband absorption and enhancing the near‐infrared (NIR) emitting properties of NIR phosphors is a key challenge to realize its multiple applications, such as solar spectrum conversion, spectral analysis, and night vision. Here, a novel NIR phosphor system MTiTaO6: Cr3+ (M = Al3+, Ga3+, Sc3+), with an excitation spectrum as broad as 421 nm and enhanced NIR emission is reported. It is the widest excitation spectrum among the known Cr3+‐doped NIR phosphors. Structural and spectroscopic analysis shows that the ultra‐broadband excitation spectrum originates from the overlap of multiple luminescence centers. Additionally, the emission peak is red‐shifted from 816 to 871 nm with increasing M ion radius, and the emission intensity is enhanced, which not only makes the emission spectra more compatible with the response curve of c‐Si solar cells, but also gives it an advantage in NIR spectroscopy applications. Comparison of the excitation spectra with the solar spectrum and spectral analysis of the emission spectra of water and alcohol demonstrate its promising applications.

Efficient Double-Layer Evaporators with Adjustable Pores for Sustainable Solar Evaporation.

Solar-driven desalination technology is currently an important way to obtain freshwater resources. Significantly, porous materials are used as substrate materials of interface solar evaporator, and their specific impact of water transport property and thermal management during evaporation is worth exploring. In this paper, poly(vinyl alcohol) (PVA) sponges were prepared by a chemical foaming method, adjusted the PVA polymerization degree, and formaldehyde-hydroxyl ratio to regulate the pore size, and polypyrrole (PPy) was grown in situ on the surface skeleton of PVA sponge to construct a new interfacial solar evaporator (PPy/PVA) with different pore structures. As the size of the evaporator pore changes, the trends in the water transport property and thermal management capability are opposite. Among them, the PPy/PVA-3 evaporator achieves a surface temperature of 38.9 °C and an evaporation rate of 1.764 kg m-2 h-1 under 1 Sun light. And the evaporation efficiency exceeds the theoretical limit (100%). This is because it has the optimal pore structure to balance the competition mechanism between the two aspects. At the same time, the evaporator exhibits good cyclability, stability, and self-cleaning capability. In addition, the evaporator has practical applicability with good purification of both organic dyes and seawater.

A Simple Micro/Nano‐Porous Structure With Day‐Night Dynamic Thermal Control and High Thermal Conductivity for Enhanced Thermoelectric Power Generation

AbstractThe main challenge of an all‐weather power generation system that combines radiative cooling and thermoelectricity is to dynamically regulate the temperature sources at both ends of the thermoelectric device. Previous studies have used stacked and flipped structures, thermochromic materials, and other methods. However, the above methods have complex structures, low thermal conductivity efficiency, and difficult‐to‐prepare materials. Therefore, in this paper, a porous structure of carbon nanomaterials with simple preparation, dynamically adjustable heat source during day and night, and high thermal conductivity in combination with thermoelectric devices with ultra‐high electrical efficiency is proposed. The structure has a solar spectrum absorption of 98.6%. Graphene film is used as a substrate material to enhance the longitudinal thermal conductivity. Experiments showed that the maximum voltage during day and night can reach 847 and 106 mV, the maximum temperature difference is 12.63 and 1.42 °C, and the maximum power density is 2112.96 mW m−2 when combined with thermoelectric devices. Simulation models are used to analyze the environmental sensitivity of power generation units and to predict their power generation potential. This work provides superior photothermal/radiative cooling structures combined with thermoelectric elements for efficient all‐weather energy conversion and power output.

Free-form surface-based polar-axis rotational direct solar radiation spectrum measurements

Accurate measurements of direct solar radiation spectra are crucial for atmospheric science, climatology, agriculture, and solar energy. Existing systems depend on costly dual-axis tracking devices, leading to high maintenance and error rates. This study presents a free-form surface-based polar-axis rotating solar direct radiation spectrometer, enabling year-round measurements across all latitudes without mobile tracking. The system operates in the 380–780 nm range with a spectral resolution better than 2 nm. Simulation results demonstrate spectral curve area errors between 0.68% and 1.22%, and outdoor experiments in Changchun, China, confirm the accuracy of measurements against the AM1.5 G standard.

Innovative Power Strategies for CubeSats: Enhancing Solar Energy Capture and Efficient Storage Solutions

CubeSats, a revolutionary class of small satellites, have significantly democratized access to space by offering compact, cost-effective, and highly versatile platforms for scientific, commercial, and educational applications. These miniaturized spacecrafts have become indispensable tools for conducting Earth observation, atmospheric studies, deep-space exploration, and technology demonstrations. However, the efficient management of power systems remains a critical challenge due to the constraints imposed by their small size, limited surface area for solar energy harvesting, and the harsh conditions of space. This paper explores innovative approaches to optimizing the energy systems of CubeSats, focusing on advancements in solar energy harvesting, energy storage technologies, and power management strategies. It highlights the potential of high- efficiency photovoltaic materials, such as multi-junction and perovskite solar cells, to enhance energy capture by utilizing broader portions of the solar spectrum. The study also examines energy storage technologies, including lithium-ion, lithium-polymer, and emerging solid-state batteries, comparing their performance, reliability, and applicability in space missions. Furthermore, hybrid energy storage systems, which combine different storage technologies like batteries and supercapacitors, are analyzed for their ability to dynamically balance energy supply and demand, ensuring stability and efficiency under variable conditions. The research delves into advanced optimization techniques, such as Maximum Power Point Tracking (MPPT) algorithms, which adaptively maximize energy extraction from solar panels, and thermal management strategies that mitigate efficiency losses due to overheating. Load scheduling, depth-of-discharge control, and real-time diagnostics are discussed as critical strategies to extend battery lifespan and ensure continuous operation. Mathematical models and experimental data are integrated to validate these techniques and provide actionable insights for the design and operation of CubeSat energy systems. By addressing the unique challenges of CubeSat power management, this study contributes to the development of robust, sustainable, and high-performance energy solutions. These advancements not only enhance CubeSat mission capabilities and longevity but also pave the way for more ambitious applications, including interplanetary exploration and multi- satellite constellations. The findings of this research are intended to benefit academia, space agencies, and industries, fostering innovation in small satellite technology and expanding the possibilities for cost-effective and impactful space exploration.

Photovoltaic-Thermal Side-Absorption Concentrated Module with Micro-Structures as Spectrum-Division Component for a Hybrid-Collecting Reflection Solar System

A photovoltaic-thermal side-absorption concentrated module (PT-SACM) based on spectrum division for photovoltaic-thermal hybrid applications is carried out. In order to reduce the absorption by materials and the axial-chromatic aberration caused by the transmissive optical system and to improve the performance of the entire system, a reflective system, the parabolic mirror array, fabricated by the ultra-precision diamond turning technology, is proposed herein. For the purposes of spectrum division, thinner volume, lightweight, and wide acceptance angle, the proposed module is designed with a diffraction optical element (DOE), a light-guide plate with a micro-structure array and a parabolic mirror array. Among them, the DOE can separate the solar spectrum into the visible band, which is converted to electrical energy via photovoltaics, and the infrared band, whose thermal energy is collected. Experimental measurements show that the overall optical efficiency of the entire system reached 38.32%, while a deviation percentage of 3.5% is calculated based on the simulation. The system has successfully demonstrated the separation of visible and infrared bands of the solar spectrum. Meanwhile, the lateral displacement between the micro-structures of the light-guide plate and the focus of the parabolic mirror array can be used to compensate for the angular deviation of the sun incidence, thereby achieving wide-angle acceptance via the proposed solar concentration system.

Vanadium pentoxide-coated smart windows for passive radiative cooling applications

Passive radiative cooling (PRC)-based smart windows are emerging as a potential solution for reducing the energy needs of buildings, both homes and offices alike. While a lot of research has occurred in this regard, vanadium oxide-based materials are studied very recently. We carry out a finite element method-based simulation study to understand the behavior of using vanadium pentoxide (V2O5) as a coating on glass windows. The proposed design can help in saving energy by emitting cooler rays inside the building when direct sun rays fall on the coated glass surface, thereby reducing internal room temperatures. It is also a solution to global warming, as the emissions from ACs will reduce due to the lower inside temperature of buildings thereby reducing demand on power usage. We found that the ambient temperature ([Formula: see text]) inside buildings can be reduced by up to [Formula: see text] when the outer temperature is [Formula: see text]. Also, the surface radiosity of V2O5 windows is twice that of glass windows and increases with the outer temperature. Lastly, we compare the performance of V2O5 with that of VO2 and find that they have similar characteristics of radiant exitance, surface radiosity and surface emissivity of long-wave infrared (LWIR) rays thus making V2O5 as a possible candidate for PRC which is low cost and affordable to many people.

High‐Efficiency PbS Quantum Dots Infrared Solar Cells via Numerical Simulation and Experimental Optimization

AbstractLow‐bandgap lead sulfide quantum dots (PbS QDs) can efficiently harness the infrared (IR) light in the solar spectrum beyond 1100 nm, showing great application potential in the bottom subcells of tandem solar cells. However, achieving further efficiency improvements in PbS QDs IR solar cells still faces many challenges. In this work, the effects of the absorber layer thickness, the carrier mobility in the absorber layer, the defect density in the absorber layer and at the absorber/electron transfer layer (ETL) interface, and the doping density of the ETL and hole transfer layer (HTL) on the performance of PbS QDs (≈0.95 eV) IR solar cells are systematically investigated through SCAPS‐1D simulation. A theoretical efficiency of 16.95% and 2.15% is calculated for PbS QDs IR solar cells under AM 1.5 and 1100 nm‐filtered illumination, respectively. Based on the simulation results, the corresponding PbS QDs IR solar cells are fabricated with an efficiency of 11.53% under AM 1.5 illumination, a remarkable 1100 nm‐filtered efficiency of 1.30%, and a high external quantum efficiency of 70.50% at 1290 nm. Hence, these findings will accelerate the optimization of the performance of PbS QDs IR solar cells approaching their theoretical efficiency limit.

Hydrogel‐Based Photothermal‐Catalytic Membrane for Efficient Cogeneration of Freshwater and Hydrogen in Membrane Distillation System

AbstractPhotothermal‐catalytic (PTC) process is a promising way to produce freshwater and clean hydrogen by integrating solar‐driven desalination and water splitting. However, efficient solar spectrum utilization coupled with effective mass and thermal management poses key challenges in developing multifunctional PTC systems. Here, a highly stable hydrogel membrane (CdS/MX‐HM) that incorporates MXene and in‐situ generated CdS as the PTC materials into a customized vacuum membrane distillation (VMD) setup is demonstrated. The CdS/MXene composites utilize the full solar spectrum, with MXene contributing to photothermal ability and serving as a co‐catalyst to enhance photocatalytic performance, which are effectively integrated into the membrane system. These functional materials are immobilized within the hydrophilic PVA/chitosan hydrogel layer, which creates a supramolecular network that provides excellent stability and protection while offering an interface for PTC processes. Supported by the hydrophobic PTFE membrane substrate, the integrated system enables fast gas transfer to the permeate, completing the dual‐function design. Through systematic optimization of membrane structure and operational parameters, the PTC‐VMD system achieves a water flux of 1.63 kg m−2 h−¹ and a hydrogen production rate of 3099 µmol m−2 h−1 under one sun irradiation, demonstrating its potential as a sustainable solution for the water‐energy nexus challenge.