High Solar Energy Conversion Efficiency Research Articles

Mesoporous cellulose/TiO2/SiO2/TiN-based nanocomposite hydrogels for efficient solar steam evaporation: low thermal conductivity and high light-heat conversion

Solar steam evaporation is regarded as a green and efficient method to achieve desalination and purification. However, the low-efficiency photothermal conversion of its evaporator is an obstacle to widespread application. Focusing on the interface evaporation method through photothermal conversion, the current bottleneck of the technology is that it is impossible to achieve in-depth interface control of the incident light path to obtain higher water evaporation efficiency. We propose a mesoporous cellulose-based hydrogel for the manufacture of a high-efficiency solar steam evaporator. This type of solar evaporator achieves an enhanced capillary force and optical path extension to increase the photothermal conversion efficiency and evaporation rate. These evaporation performance advantages can all be attributed to the dense mesoporous structure, low thermal conductivity, and high light absorption efficiency. The results showed that under a solar light intensity of 1.5 kW m−2, the mesoporous structure of the MCNT–TiO2–SiO2–TiN hydrogel-based evaporator has an excellent evaporation rate (1.853 kg m−2 h−1) and high solar energy conversion efficiency (77.39%) due to the low thermal conductivity (0.71997 W m−1 k−1), high light absorption efficiency (98.3%, wavelength 190–3000 nm) and good hydrophilic properties (XRD and FT-IR tests). Our results demonstrate a new full-hydrogel solar steam evaporation method by using a simple, easily obtained, reusable, and low-cost solar desalination and purification system based on evaporation can yield fresh water from seawater and sewage. The evaporation technique can be used to produce a simple, easily obtained, reusable, and low-cost solar desalination and purification system for pure freshwater resources from seawater and sewage.

Solar Thermal Energy Conversion Enhanced by Selective Metafilm Absorber Under Multiple Solar Concentrations at High Temperatures

Concentrating solar power, particularly parabolic trough system with solar concentrations less than 50, requires spectrally selective solar absorbers that are thermally stable at high temperatures of 400°C above to achieve high efficiency. In this work, the solar-thermal performance of a selective multilayer metafilm absorber is characterized along with a black absorber for comparison by a lab-scale experimental setup that measures the steady-state absorber temperature under multiple solar concentrations. Heat transfer analysis is employed to elucidate different heat transfer modes and validate the solar-thermal experiment. Due to the superior spectral selectivity and excellent thermal stability, the metafilm absorber deposited on the cost-effective stainless steel foil could achieve the solar-thermal efficiency 57% at a steady-state temperature of 371°C under 10 suns during the lab-scale experiment with losses, while a highest efficiency of 83% was projected under the same conditions for practical solar thermal applications. The results here will facilitate the research and development of novel solar materials for high-efficiency solar thermal energy conversion.

Beyond lotus: Plasma nanostructuring enables efficient energy and water conversion and use

Over millions of years, natural evolution created intricate plant microstructures to most effectively convert and use energy and water. Here we use one-step plasma carbonization and surface nanostructuring of microscopic textures of sacred lotus (Nelumbo nucifera), to dramatically surpass its natural performance in light harvesting, water transport and evaporation. The plasma exposure produces vertically-oriented graphenes (VGs) on the lotus micro-textured surfaces (lotus/VG), without any external carbon source. The nanostructures exhibit high photonic absorption of 99.2% (~twice the pristine lotus), customized centralized water pathway, run-through channels and super-hydrophilicity for ultrafast water transport (~5 times the pristine lotus), and potential for scalable, low cost production. The lotus/VG evaporator exhibits a high solar energy conversion efficiency (~90%) at 1 sun, competitive with synthetic materials. Furthermore, the lotus/VG nanostructures are applied for sludge drying and wastewater treatment, demonstrating great potential of this nanotechnology-enhanced natural material for renewable solar energy utilization.

Sugarcane‐Based Photothermal Materials for Efficient Solar Steam Generation

AbstractSolar steam generation is a promising strategy for harvesting solar energy for diverse applications such as desalination and wastewater treatment. Here, we demonstrate the fabrication of polypyrrole modified sugarcane (PPy‐SC) as efficient photothermal material for solar steam generation. The PPy‐SC possesses various close‐packed open channels in horizontal plane and super hydrophilic wettability which is beneficial for rapid transportation of water molecules. In combination with its abundant porosity (47%), low apparent density (80 mg cm−3), low thermal conductivity (0.042 W m−1 K−1), and broad light absorption (90%). The prepared PPy‐SC exhibits a high evaporation rate of 1.59 kg m−2 h−1 and conversion efficiency of 90.6%, under 1 sun irradiation. In addition, the PPy‐SC also shows good performance in desalination. With the merits of low‐cost, eco‐friendly, simple fabrication process, high solar energy conversion efficiency, the PPy‐SC shows great potential as an efficient photothermal material for solar steam generation.

Engineering the Optoelectronic Properties of Colloidal Alloyed Copper Chalcogenide Quantum Dots for High‐Efficiency Solar Energy Conversion

Colloidal alloyed copper chalcogenide Cu2 − xSe1 − ySy (CuSeS) quantum dots (QDs) are promising building blocks for solar energy applications because of their unique size/composition‐tunable optical bandgap, which is well matched to the sunlight spectrum. Nevertheless, poor charge separation/transfer and low photostability induced by their intrinsically abundant surface defects/traps tremendously hinder the realization of high‐performance solar energy conversion systems such as solar‐driven photoelectrochemical (PEC) devices. Herein, the synthesis of copper chalcogenide CuSeS core QDs with effective CdS shell passivation is presented. These core/shell QDs exhibit optimized optoelectronic properties with a particularly ultralong lifetime, indicating the formation of type‐II band structure for efficient spatial charge separation, which is further probed using ultrafast transient absorption (TA) spectroscopy. To demonstrate the feasibility of solar energy conversion, solar‐driven PEC cells using such core/shell QDs as light‐converters are fabricated, yielding an impressive saturated photocurrent density of ≈4 mA cm−2 with preeminent durability under 1 sun illumination. This finding highlights a potential technique to engineer the optoelectronic properties of colloidal alloyed copper chalcogenide nanomaterials for high efficiency and stable solar energy conversion devices.

Perovskite solar cell-thermoelectric tandem system with a high efficiency of over 23%

Photovoltaic-thermoelectric (PV-TE) tandem system has been considered as a viable approach to fully exploit solar energy by making full use of both solar light and solar heat generation. Herein, we demonstrate an efficient perovskite solar cell (PSC)-thermoelectric (TE) hybrid system with four-terminal configuration. To balance the light-to-electricity and heat-to-electricity efficiency and ultimately realize high solar energy conversion efficiency, we performed both simulation and experiment by tuning the bandgap of top PSC. Using perovskite with a composition of CH3NH3Pb(I0.95Br0.05)3 (band gap: 1.61 eV), we achieved a state-of-the-art efficiency of over 23%, with 18.3% from the PSC and the rest contributed by heat conversion using TE module. Our work proves that the low-grade heat produced by PSCs can be recovered and utilized by thermoelectric modules, and provides a promising route to improve the utilization rate of solar radiation based on PSCs.

Coupling Plasmonic and Cocatalyst Nanoparticles on N⁻TiO₂ for Visible-Light-Driven Catalytic Organic Synthesis.

The use of the surface plasmon resonance (SPR) effect of plasmonic metal nanocomposites to promote photocarrier generation is a strongly emerging field for improving the catalytic performance under visible-light irradiation. In this study, a novel plasmonic photocatalyst, AuPt/N–TiO2, was prepared via a photo-deposition–calcination technique. The Au nanoparticles (NPs) were used herein to harvest visible-light energy via the SPR effect, and Pt NPs were employed as a cocatalyst for trapping the energetic electrons from the semiconductor, leading to a high solar-energy conversion efficiency. The Au2Pt2/N–TiO2 catalyst, herein with the irradiation wavelength in the range 460–800 nm, exhibited a reaction rate ~24 times greater than that of TiO2, and the apparent quantum yield at 500 nm reached 5.86%, indicative of the successful functionalization of N–TiO2 by the integration of Au plasmonic NPs and the Pt cocatalyst. Also, we investigated the effects of two parameters, light source intensity and wavelength, in photocatalytic reactions. It is indicated that the as-prepared AuPt/N–TiO2 photocatalyst can cause selective oxidation of benzyl alcohol under visible-light irradiation with a markedly enhanced selectivity and yield.

First principles evaluation on photocatalytic suitability of 2H structured and [0001] oriented WS2 nanosheets and nanotubes

Pristine WS2 multilayer nanosheets (NSs), which thickness hNS varies from 1 to 12 monolayers (MLs), as well as single- and multi-walled nanotubes (SW and MW NTs) of different chirality, which diameter dNT exceeds 1.9 nm, display photocatalytic suitability to split H2O molecules. Obviously, such a phenomenon can occur since the band gap of these nanostructures corresponds to the energy range of visible light between the red and violet edges of spectrum (1.55 eV < Δεgap < 2.65 eV). For all the studied WS2 NSs and NTs, the levels of the top of the valence band and the bottom of the conduction band must be properly aligned relatively to H2O oxidation and reduction potentials separated by 1.23 eV: εVB < εO2/H2O < εH+/H2 < εCB. The values of Δεgap decrease with growth of hNS and increase with enlargement of dNT. 1 ML nanosheet can be considered as a limit of infinite SW NT thickness growth (dNT→∞), which band gap increases up to ∼2.65 eV. First principles calculations have been performed using the hybrid DFT-HF method (HSE06 Hamiltonian) adapted for 2H WS2 bulk. The highest solar energy conversion efficiency (15-18%) expected at Δεgap = 2.0-2.2 eV (yellow-green range) has been found for 2 ML thick (stoichiometric) WS2 (0001) NS as well as WS2 NTs with diameters 2.7-3.2 nm (irrespectively on morphology and chirality indices n of nanotubes). Moreover, unlike discrete variation of hNS magnitudes, tuning of dNT values provides much higher energy resolution.

Nature-inspired salt resistant polypyrrole–wood for highly efficient solar steam generation

Solar steam generation has emerged as a promising and sustainable method of addressing the water shortage issue. The fabricated PPy–wood exhibits high solar energy conversion efficiency and excellent salt resistant performance.

Hierarchical macro-mesoporous g-C3N4 with an inverse opal structure and vacancies for high-efficiency solar energy conversion and environmental remediation.

Hierarchical macro-mesoporous structures with an efficient mass transfer and light harvesting offer great advantages for photocatalysis. Nitrogen vacancy modified ordered hierarchical macro-mesoporous g-C3N4 (Nv MM CN) was fabricated by a dual-templating method combining an ordered SiO2 colloidal crystal and NH4Cl. The as-prepared Nv MM CN was applied for photocatalytic degradation of antibiotics and production of hydrogen. Nv MM CN showed 27 times higher photocatalytic degradation efficiency and 7.5 times higher hydrogen production than bulk g-C3N4 (Bulk CN) under visible light irradiation. The 3D well interconnected macro-mesoporous structure and the porous system accelerated adsorption as well as the reaction rate and the inverse opal photonic crystals provided multiple scattering effects to strengthen light absorption. Meanwhile, the nitrogen vacancy introduced acted as a separation center to capture electrons or holes to improve the separation efficiency of charges. This efficient, stable, and environmentally friendly visible light-driven Nv MM CN may be an alternative for effective implementation in wide-ranging energy and environmental applications.

Fabrication of bilayered attapulgite for solar steam generation with high conversion efficiency

Solar steam generation has been attracting wide attention for boosting the evolution of solar-energy-harvesting technology. Here, we demonstrate the fabrication of a novel bilayer photothermal material based on attapulgite/poly acrylamide composite (APAC), which was prepared by the solution polymerization of acrylamide (AM) in the presence of attapulgite using N, N′-Methylene bisacrylamide (MBA) as a crosslinker, for efficient solar steam generation. The APAC shows better thermal stability with a decomposition temperature of 250 °C, good mechanical property with a compress strength of up to 125 KPa at 75% strain and a low apparent density (0.0191 g·cm−3) with abundant porosity accompanying with a low thermal conductivity (0.07 W m−1 K−1). To enhance the light absorption of APAC, a thin carbon layer was created on the surface of APAC via a facile flame treatment. Under our conditions, the bilayered APAC shows a high vapor rate of 1.2 kg m−2 h−1 under 1 sun illumination, equal to 85% solar-to-vapor efficiency. With the merits of cost-efficient, scalable manufacture, high solar energy conversion efficiency, the APAC may hold the great potential as high-performance photothermal materials for solar energy generation.

Highly Improved Solar Energy Harvesting for Fuel Production from CO2 by a Newly Designed Graphene Film Photocatalyst

Our growing energy demands must be met by a sustainable supply with reduced carbon intensity. One of the most exciting prospects to realize this goal is the photocatalyst-biocatalyst integrated artificial photosynthesis system which affords solar fuel/chemicals in high selectivity from CO2. Graphene based photocatalysts are highly suitable for the system, but their industrial scale use requires immobilization for improved separation and recovery of the photocatalyst. Therefore for practical purposes, design and fabrication of film type graphene photocatalyst with higher solar energy conversion efficiency is an absolute necessity. As a means to achieve this, we report herein the successful development of a new type of flexible graphene film photocatalyst that leads to >225% rise in visible light harvesting efficiency of the resultant photocatalyst-biocatalyst integrated artificial photosynthesis system for highly selective solar fuel production from CO2 compared to conventional spin coated graphene film photocatalyst. It is an important step towards the design of a new pool of graphene film based photocatalysts for artificial photosynthesis of solar fuels from CO2.

Revealing Photoluminescence Modulation from Layered Halide Perovskite Microcrystals upon Cyclic Compression.

Halide perovskites show promise for high-efficiency solar energy conversion and light-emitting diode devices owing to their bandgap, which falls within the visible optical range. However, due to their rigidity, GPa pressures are necessary to control the complex interplay between their electronic and crystallographic structure. Layered perovskites are likely to be controlled using much lower pressures by exploiting the optical anisotropy of the embedded organic molecules in the structure. This work introduces layered perovskite microplatelets and demonstrates the extreme sensitivity of their emission to cyclic mechanical loading in the range of tens of MPa. A drastic change in their emission is observed in situ, from near-white to an enhanced blue color. This process is reversible, as is evident from a hysteresis loop in the photoluminescence (PL) intensity of the microplatelets. A combination of experimental analysis and computational modelling shows that such behavior cannot be attributed to changes in the crystallographic structure of the flakes. Instead, it suggests that, thanks to their structural anisotropy, microplate alignment and reorientation are responsible for the observed PL modulation. The possibility to tune the optical emission of layered perovskite crystals via low pressures makes them highly interesting as active materials in applications where stress sensing or light modulation is desired.

Electronic and optical properties of strained noble metals: Implications for applications based on LSPR

The localized surface plasmon resonance (LSPR) of noble metal nanoparticles provides a means to significantly enhance light-matter interaction. Thus, it is recently introduced into photovoltaics and photocatalysis for enhancing the transformation of solar light, where the efficiency of intra- and inter-band electron transitions fundamentally affects the overall performance of the systems. Considering the commonness and tunability of strain in nanoparticles, in this work we examine its potential effects on the intra- and inter-band electron transitions and related plasmonic properties of noble metals by the first-principles calculations and Drude theory. It is meaningful to find that strain can significantly modulate the electronic structures of noble metals that are closely related to the sp intra- and d–sp inter-band electron transitions. As a consequence, compressive strain notably increases the intra-band, but decrease the inter-band electron transition probabilities in the visible and near-infrared spectral range. Moreover, it significantly increases the near-field enhancement and light absorption efficiency for the LSPR in the visible and near-infrared range. Whereas the effect of tensile strain is exactly opposite. These results are very useful as guides in optimizing the nanostructure design for higher solar energy conversion efficiency and optoelectronic devices based on the LSPR of noble metals.

Surface Reorganization Leads to Enhanced Photocatalytic Activity in Defective BiOCl

Introducing defects into semiconductor photocatalysts has been identified as an effective approach to extend the visible-light absorption and achieve high-efficiency solar energy conversion. However, the band gap model system of defect states may not truly describe the evolutions in real materials as the narrower band gap would limit the photocatalytic activity via suppressing the charge separation. Here, we report that reorganizing the surface termination in a defective semiconductor plays a key role in determining the photocatalytic performance. We directly observed that the surface reorganizations are accompanied by the formation of defects in layered structured bismuth oxychloride (BiOCl). Both experimental and theoretical results demonstrate that varying terminations have strong effects on the electronic structure and electron–hole pair recombination, which is shown to be the driving force of the promotion of visible-light photocatalytic activity in BiOCl. We also reveal that the surface reorganizati...

Formation of Large Grain and Compact CH3NH3Pb(I&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$_{\rm 1\hbox{--}x}$&lt;/tex-math&gt; &lt;/inline-formula&gt;Br&lt;italic&gt; &lt;sub&gt;x&lt;/sub&gt; &lt;/italic&gt;)3 Film by Multisteps Solvent Postannealing for High-Efficiency Perovskite Solar Cells

The reaction toward MAPb(I $_{\rm 1\hbox{--}x}$ Br x )3 by the perovskite precursor is difficult to form a continuous film over a large area. In this paper, we develop a multisteps solvent-postannealing method based on a high-coverage MAPbI3 film a template for preparing uniform and compact MAPb(I $_{\rm 1\hbox{--}x}$ Br x )3 film with film-through large grain and uniform distribution of Br elements. The formed MAPbI3 film must be annealed in the mixture vapor of dimethyl sulfoxide and aqueous HBr to achieve the simultaneous modification of composition and crystallinity, and then it has to be repaired further using CH3NH2 vapor annealing to eliminate the defects of the film surface and crystal grain boundaries. The corresponding perovskite solar cells (PSCs) yield a maximum power conversion efficiency of 17.23% with an open-circuit voltage ( V oc) of 1.025 V, a short-circuit current ( J sc) of 20.88 $\text{mA}\cdot\text{cm}^{-\text{2}}$ , and a fill factor (FF) of 80.54%, based on a structure of ITO/PEDOT:PSS/MAPb(I $_{\rm 1\hbox{--}x}$ Br x )3/PC61BM/Bphen/Ag, with an enhancement of 18% compared with that of the optimized MAPbI3 PSCs because of the simultaneous increase in V oc, J sc, and FF. This paper provides a feasible and effective method to fabricate high-quality MAPb(I $_{\rm 1\hbox{--}x}$ Br x )3 films for high-efficiency solar energy conversion devices.

Turnip-inspired BiVO4/CuSCN nanostructure with close to 100% suppression of surface recombination for solar water splitting

Inspired by the morphologies and function of the root and the stalk of a turnip, which has evolved with the unique pattern of growth for enhancing transport phenomenon, a novel architecture of BiVO4/CuSCN architecture is fabricated on fluorine-doped tin oxide coated glass by initially fabricating bulky BiVO4 film (the root) and subsequently depositing p-type CuSCN nanorods (the stalk). With the creation of BiVO4/CuSCN nanorod heterojunction photoanodes, the photocurrent density increases to 1.78 mA cm−2 compared to 1.22 mA cm−2 of bare BiVO4 at 1.23 V vs. reversible hydrogen electrode. More importantly, the onset potential for oxygen evolution reaction exhibits a dramatic cathodic shift (~ 230 mV). The heterojunction also possesses internal quantum efficiency of approximately 50% in the range from 350 to 450 nm with relatively high solar energy conversion efficiency (0.5%) and much higher oxidation efficiency (~ 90%). The unique electrode architecture design favoring the simple water splitting process over conventionally fabricated electrode by providing more active sites and facilitates transportation and consumption of photoinduced holes could open up a new route for the high-efficiency photoanodes.

Cylindrical thermoelectric generator with water heating system for high solar energy conversion efficiency

Thermoelectric generator (TEG) with water heating system, which utilizes solar energy with a high total energy conversion efficiency, is promising environmental technology for eco-housing and factories to reduce their carbon footprints. In this study, a newly developed cylindrical TEG consisting of ring-disk thermoelectric material is proposed showing that the total energy conversion efficiency is higher than that of a conventional pillar-type TEG. The cylindrical TEG is implemented using high-performance CoSb3-based filled skutterudite thermoelectric materials and a unique 45Ni-55Fe electrode as the hot-side junction. The solar TEG performance is demonstrated under the real sunlight, which is concentrated by a Fresnel lens. The maximum thermoelectric efficiency of the presented solar TEG is 1.8%, with a water heating efficiency of 59% when the temperature difference across the TEG is 428 °C. Further improvement should be achieved by lowering the internal resistance of the TEG and increasing the average dimensionless figure of merit of the thermoelectric materials.

Facile synthesis of interlocking g-C3N4/CdS photoanode for stable photoelectrochemical hydrogen production

A simple and facile two-step method, including electrophoretic deposition and chemical bath deposition strategies, has been used to fabricate a novel interlocking g-C3N4/CdS photoanode on conductive substrate. Integrating a large area of intercontact g-C3N4/CdS heterojunction with an intimate connection between the photocatalysts and the substrate, the separation and migration of the photogenerated carriers by g-C3N4 and CdS are significantly improved, and the internal resistance of the photoanode is effectively reduced. The optimal g-C3N4/CdS photoanode exhibits an excellent visible light photocurrent density of 5.4 mA cm-2 at 0.0 V bias (vs. Ag/AgCl) and the photoelectrochemical H2 production rate reaches 81.1 μmol h-1 cm-2. Moreover, the stability of this interlocking g-C3N4/CdS photoanode not only reflects in a 9-hour long time recycling photoelectrochemical H2 production test, but also in an outstanding steady structure which even be stabilized in an ultrasonic treatment. The present study provides a practical and convenient technique to develop such an earth abound and low-cost CdS/C3N4 photoanode which can be used for high efficiency and stable photoelectrochemical solar energy conversion.

Influence of SrTi1-xCoxO3 NPs on electrocatalytic activity of SrTi1-xCoxO3 NPs/PEDOT-PSS counter electrodes for high efficiency dye sensitized solar cells

Dye sensitized solar cell (DSSC) based on the improvement of cell performance by modification of cell components is still an interesting issue to be explored. Consequently, various natural dyes and materials/compounds have been investigated to replace the expensive synthetic dye and Pt counter electrode (CE), respectively. According to our previous work on the study of transition metal doped SrTiO3 nanoparticles (NPs), it was obvious that various properties of these materials could be altered with potential to apply for different devices. In this work, it is our purpose to search for a novel composite material based on Co-doped SrTiO3 NPs to replace Pt CE. Therefore, composite SrTi1-xCoxO3 NPs/PEDOT-PSS pastes (x = 0, 0.025, 0.05, 0.075 and 0.1) were prepared and tested for CE of DSSC. Interestingly, the cyclic voltammetry (CV) measurements indicated that SrTi1-xCoxO3 NPs could function as an excellent catalyst in iodide/triiodide redox reaction. Moreover, electrochemical impedance spectroscopy (EIS) results showed the consistent reduction of charge transfer resistance of SrTi1-xCoxO3 NPs/PEDOT-PSS CE. Surprisingly, the highest solar energy conversion efficiency of 8.39%, compared with 8.27% of Pt CE, was achieved in a cell with SrTi0.925Co0.075O3 NPs/PEDOT-PSS CE.