Solar Energy Harvesting Applications Research Articles

Ultrasonic spray deposition as a new route to luminescent MOF film synthesis

The deposition of high-quality metal-organic framework (MOF) films is still challenging but offers potential applications in gas storage, catalysis, sensing, lighting, and solar energy harvesting. This work reports a single-step, simple, fast and inexpensive method for in situ synthesis and deposition of crystalline luminescent Tb2(BDC)3 (Tb = terbium) (BDC = 1,4-benzenedicarboxylate) MOF films using ultrasonic spray deposition on top of several types of substrates including glass slides, metal oxides films, filter paper, and polyimide sheets. The glass supported films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), profilometry, infrared (IR), and luminescence spectroscopies. As expected, the emission spectra present high-intensity characteristic emission bands of the sensitized terbium luminescence for all the films. Nevertheless, the temperature of the substrate, during deposition, plays a crucial role in the final structural and morphological characteristics of the MOFs, which in turn, dramatically modifies the excitation features. The MOF-film synthesis/deposition method here reported can be extended to other MOF structures and substrates.

Subwavelength nonimaging light concentrators for the harvesting of the solar radiation

Light trapping and the broadband absorption of the solar radiation is of interest to various solar energy harvesting applications. In the current work, we report a new paradigm for light trapping, that is light trapping based on arrays of subwavelength nonimaging light concentrators (NLCs). We numerically show that silicon NLC arrays provide >75% broadband absorption enhancement of the solar radiation compared with that of optimized nanopillar arrays. The paper focuses on free-floating arrays of subwavelength compound parabolic concentrators (henceforth CPC arrays) as a case study. The calculations reveal that CPC arrays function as anti-transmission layers as only few photons transverse the CPC arrays which is in contrast to nanopillar arrays that function as anti-reflection layers. We show that the absorption enhancement in CPC arrays is due to efficient occupation of Mie modes which is motivated by the unique CPC geometry, and we demonstrate light trapping at the Yablonovitch limit. Finally, we examine the performance of a photovoltaic cell based on CPC arrays with respect to base doping levels and surface recombination. We show that the short-circuit current density of the CPC-based cell is >75% higher than the short-circuit current density of a photovoltaic cell based on optimized nanopillar arrays. We believe that light trapping based on NLC arrays paves the way to various applications such as ultra-thin photovoltaic cells.

Dual plasmonic Au/TiN nanofluids for efficient solar photothermal conversion

Fabrication highly efficient photothermal conversion nanofluids is a fascinating topic in solar energy harvesting applications. Herein, we present TiN is an excellent alternative plasmonic nanofluid for solar thermal conversion. The optical absorption property and the photothermal conversion performance of titanium nitride (TiN) are superior to another five traditional materials such as carbon nanotube, graphene, Au, Ag and metal sulfide (CuS). Dual localized surface plasmon resonance (LSPR) effect between Au and TiN nanoparticles make the hybrid nanocomposite (Au/TiN) possess superior optical absorption to TiN at the same concentration. The maximal temperature rise of 100 ppm TiN after irradiation for 20 min is 14.2 °C. The photothermal conversion efficiency of TiN is much higher than another five conventional nanofluids. All Au/TiN nanofluids with different Au loadings show higher maximal temperature rise than TiN, indicating dual LSPR effect is beneficial for better photo-thermal conversion performance.

N-N type core-shell heterojunction engineering with MoO3 over ZnO nanorod cores for enhanced solar energy harvesting application in a photoelectrochemical cell

Herein, we report an easy and scalable chemical bath deposition and spin coating route of n-n hetero-architecture engineering to fabricate MoO3-ZnO core-shell nanorods (NRs) based photoanode, which is indeed the first time demonstration of this particular nano-heterojunction for solar energy conversion and hydrogen energy generation in a photoelectrochemical (PEC) cell. We further tune the MoO3 shell thickness by varying spin coated layer thickness. An average thickness ∼100 nm of MoO3over 450 nm ZnO NRs significantly improves the photocurrent from 3.3 to 27.6μAcm−2. A 7.5 fold increase in applied bias photon to current conversion efficiency (ABPE) value is achieved upon visible light illumination (Visible light, 10 mWcm−2) with a maximum value of 0.15% than bare ZnO NRs (0.02%). In addition, hydrogen gas (5 μmolcm−2) is evolved even at no external potential applied to the PEC cell with this MoO3-ZnO. The physical insight of the enhanced PEC performance is also elucidated. We find the n-n hetero-architecture to provide a suitable solution to maximize solar light absorption along with enhanced charge carrier separation which also boosts the charge transportation and mobility in the junction region due to suitable core-shell interfacial band alignment and modulation of interfacial electronic structure. Mainly, the MoO3 shell provides a potential solution to get more catalytically active sites and the outer Mo-O dipole layer transfers holes to the electrolyte for easy oxidation of water.

Highly broadband plasmonic Cu film modified Cu2O/TiO2 nanotube arrays for efficient photocatalytic performance

To develop an efficient photocatalyst electrode for solar energy harvesting and photocatalysis application in the visible region, broadband plasmonic Cu film combined with Cu2O/TiO2 nanotube arrays heterojunction (Cu film/Cu2O/TiNT) has been successfully fabricated by anodization combined with electrodeposition method. Interestingly, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and UV–Vis diffuse reflectance spectroscopy reveal that the combined consequence of both Cu film and Cu2O in the as-synthesized ternary composite considerably enhances light absorption in the visible spectral. This activity is attributed to the more efficient charge separation/transportation and the presence of Cu film with strong plasmon resonance (SPR) effect. Moreover, the combined effects of both Cu film and Cu2O on TiNT approved highest catalytic current density and highest photocatalytic activity on methylene blue (MB). The efficiency and the rate of MB photodegradation over the Cu film/Cu2O/TiNT were found to be triple compared to TiNT. Within only 30 min of reaction time, the photodegradation of MB reaches nearly 100%.

Self-assembled porphyrin and macrocycle derivatives: From synthesis to function

Abstract

Additive manufacturing of photoactive polymers for visible light harvesting

In recent years, 3D printing has gained a great deal of attention in the energy field, with numerous reports demonstrating its application in fabrication of electrochemical devices. The near-complete freedom of design offered by 3D printing technologies make them very appealing, since complex 3D parts can be directly fabricated. However, its application in photochemistry and solar energy harvesting remains, so far, an uncharted territory. In this work, a photoactive monomer was incorporated into commercially available 3D printing resin, which was subsequently used to successfully fabricate 3D photosensitizing structures for singlet oxygen generation. Results indicate that the SLA fabricated small-scale (0.1 ml) photoactive continuous flow reactor shows activity in singlet oxygen synthesis reaction under visible light irradiation (420 nm).

Eco-friendly AgInS2/ZnS quantum dot nanohybrids with tunable luminescent properties modulated by pH-sensitive biopolymer for potential solar energy harvesting applications

Semiconductor quantum dots (QDs) are very interesting candidates for the development of green-energy based nanomaterials and devices. However, currently they present serious concerns because the large majority of efficient QDs have been synthesized using organometallic routes with toxic heavy metals. Herein, we designed and produced novel fluorescent ternary and quaternary QD nanostructures based on AgInS2 (AIS) core and ZnS (ZAIS) shell stabilized with carboxymethyl cellulose (CMC) polymer ligand for potential applications in green solar energy harvesting. Colloidal AgInS2 QDs were prepared by co-precipitation process using a one-pot aqueous green route directly stabilized by CMC at room temperature and varying pH conditions. Then, an outlayer of ZnS was grown and thermally annealed to improve and tune their optical properties and split the emission range, leading to core–shell alloyed nanostructures. Their physicochemical and optical properties were extensively characterized, demonstrating that photoluminescent monodispersed AIS and ZAIS QDs were produced with size typically ranging from 8.5 ± 2.4 nm and 3.2 ± 1.1 nm under acidic or alkaline media, respectively. Therefore, by adjusting the parameters of synthesis, the QD nanohybrids showed tunable optical properties ranging from UV to NIR, with maxima absorption/emission in the visible-range of the light spectrum (from λ = 650 to 750 nm). More importantly, the optical properties demonstrated remarkable enhancement of quantum yield of over one order of magnitude due to the combination of processing parameters and engineered core–shell nano-architecture of AgInS2–ZnS. Thus, these luminescent nanomaterials offer great perspectives for developing innovative broad spectral converters for a wide range of applications in solar energy harvesting.

Optimization of conditions for improved solar energy harvesting application by hydrothermally grown TiO2 nanorods

In this study, using the optimum annealing temperature and time for hydrothermally grown TiO2 nanorods, photooxidation of water at different pH values of the electrolyte solution is investigated. The composition, crystallinity and topographic studies of films, sintered at different temperatures of 200–500 °C for 2 h and annealed for 1–4 h at 400 °C, were evaluated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and field emission scanning electron microscopy. The sintering at high temperature and for longer time demonstrates an increase in crystallinity, but at the same time agglomeration of nanorods for prolonged heating and at high temperature leads to cracking at the surface of the films. Further, UV–Vis spectroscopic studies revealed prolonged heating and high-temperature sintering resulted in a red shift in light absorption edge of the films. The chronoamperometric measurement results under regular interrupted chopping revealed that the sample annealed at 400 °C for 2 h gives the best photoelectrochemical response with photocurrent density of 522 µA cm− 2 using 0.5M NaOH. The chronoamperometric response under different pH values of 13.7, 7.2 and 2.5 proved that TiO2 gives the best response under a basic pH of 13.7 and the least under acidic media. The electrochemical impedance studies provided an insight into the charge transfer mechanism under dark and illumination with Rct value of 1188.8 Ω under dark and 164.5 Ω under light conditions for the film annealed at 400 °C for 2 h.

Application of an inverse-design method to optimizing porphyrins in dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) have attracted much interest during the past few decades. However, it is still a tremendous challenge to identify organic molecules that give an optimal power conversion efficiency (PCE). Here, we apply our recently developed, inverse-design method for this issue with the special aim of identifying porphyrins with promisingly high PCE. It turns out that the calculations lead to the prediction of 15 new molecules with optimal performances and for which none so far has been studied. These porphyrin derivatives will in the near future be synthesized and subsequently tested experimentally. Our inverse-design approach, PooMa, is based on the strategy of providing suggestions for molecular systems with optimal properties. PooMa has been developed as a tool that requires minimal resources and, therefore, builds on various approximate methods. It uses genetic algorithm to screen thousands (or often more) of molecules. For each molecule, the density-functional tight-binding (DFTB) method is used for calculating the electronic properties. In the present work, five different electronic properties are determined, all of which are related to optical performance. Subsequently, a quantitative structure-property relationship (QSPR) model is constructed that can predict the PCE through those five electronic properties. Finally, we benchmark our results through more accurate DFT calculations that give further information on the predicted optimal molecules.

Step impedance resonator-based tunable perfect metamaterial absorber with polarization insensitivity for solar cell applications

In this work, a step impedance resonator (SIR)-based structure is proposed to develop a compact tunable metamaterial (MTM)-based perfect absorber for solar cell applications. This MTM absorber is able to improve the absorption over a wide range of visible frequency range from 550 to 650 THz. The absorption is high around the frequency 600 THz. The proposed model is designed based on SIR technique to achieve miniaturization. The parametric study of overall size of the proposed MTM absorber analyzed over the frequency range 430-750 THz. The thickness of dielectric spacer, and top most layer (MTM Structure) illustrates the tunable characteristics of the proposed model. A complete comparative analysis of proposed model with different dielectric spacers like AlGaAs, InAs, GaAs, and AlAs are presented with the help of absorption (S11) and transmission (S12). The proposed model is suitable for high efficiency solar cell energy harvesting applications.

A broadband plasmonic light absorber based on a tungsten meander-ring-resonator in visible region

We present the design and numerical simulations of a broadband plasmonic light absorber (PLA) based on a tungsten meander-ring-resonator (MRR) structure in visible region. The proposed PLA is composed of a periodic MRR array and a continuous tungsten (W) film separated by a dielectric substrate. Simulation results indicate that the absorbance of our PLA is up to 99.9% at 538 THz, and it is over 90% from 370 to 854 THz across the whole visible region. The simulated electric field distributions reveal that the stronger broadband absorption is caused by the excitation of localized surface plasmon (LSP), propagating surface plasmon (PSP) and guide mode resonances. Further simulation indicates that designed PLA is polarization insensitive and has a wide angle for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the impact of the geometric parameters of the designed PLA on the absorption spectrum was also studied systematically. Owing to its superior performance, the proposed PLA based on tungsten MRR can be a potential application in thermal imaging, emissivity control and solar energy harvesting.

Perfect metamaterial absorber with high fractional bandwidth for solar energy harvesting.

A new perfect metamaterial absorber (PMA) with high fractional bandwidth (FBW) is examined and verified for solar energy harvesting. Solar cells based on perfect metamaterial give a chance to increase the efficiency of the system by intensifying the solar electromagnetic wave that incident on the device. The designed structure is mostly offered in the visible frequency range so as to exploit the solar’s energy efficiently. Parametric investigations with regard to the measurements of the design structure are fulfilled to characterize the absorber. The finite-difference time-domain (FDTD) method-based CST simulator was used to keep the pattern parameters and absorbance analysis. The metamaterial shows almost 99.96% and 99.60% perfect absorption at 523.84 THz and 674.12 THz resonance frequencies. Moreover, absorption’s FBW is studied, and 39.22% FBW is found. The results confirm that the designed PMA can attain very high absorption peak at two modes such as transverse electric (TE) and transverse magnetic (TM) mode. Other than the numerical outcomes demonstrated that the suggested configuration was also polarization angle insensitive. In addition, the change of absorbance of the structure has provided a new kind of sensor applications in these frequency ranges. Therefore, the suggested metamaterial absorber offers perfect absorption for visible frequency ranges and can be used for renewable solar energy harvesting applications.

A theoretical and experimental formalism of electronic structure of BFO:Cr thin films and modulation of their electrical properties upon visible light illumination

BiFeO3 (BFO) and BiFe1-xCrxO3 (BFCO) (x = 0, 0.01, 0.02, 0.03) thin films have been fabricated using chemical solution deposition technique. The bandgap of BFO and BFCO thin films is found to be lying in the visible region making these films suitable candidates for potential solar energy harvesting applications. Density functional theory based calculations have also been performed to study the effect of B-site (Cr) doping on the electronic properties of BFO and BFCO. The BiFe1-xCrxO3 (x = 0.02) thin films exhibited well saturated PE hysteresis loops with a maximum remanent and saturation polarization of about 43 μC/cm2 and 64 μC/cm2, respectively. In contrast to pure BFO, a high value of short circuit current density (Jsc) of magnitude 766.60 μA/cm2 along with the open circuit voltage (Voc) of 106 mV was obtained for BiFe0.98Cr0.02O3 thin film structure under illumination with a laser of wavelength 470 nm and intensity 20 mW/cm2. The Au/BiFe0.98Cr0.02O3/ITO/glass heterostructure displays a remarkably enhanced value of Ion/Ioff ratio (8.4 × 104). The observed results clearly highlight the potential of Cr doped BFO thin film structure for the development of cost effective light-driven devices.

Why self-cleaning is important for solar thermal receivers?

Surface cleaning remains essential for the sustainable operation of high performance solar thermal receivers. Cleaning of optical surfaces, such as solar troughs and absorbers, requires energy intensive efforts because of the large surface area involvement such as those observed in solar farms. In addition, self-cleaning of such surfaces becomes demanding because of lowering the cleaning costs, reducing the waste of resources, such as clean water, and minimizing the complication of the mechanical systems incorporated. Self-cleaning of surfaces is associated with the low adhesion between the surface and the foreign particles; in which case, these particles can be removed easily from the surfaces in a cost-effective way. The surface energy and contact area of the surface are two main important parameters influencing the particle adhesion on the surfaces. In this case, reducing the surface energy and forming micro/nano size pillars on the surface through texturing lower the particle adhesion on the surfaces significantly. In solar thermal energy harvesting applications, metallic or composite materials are used and texturing the surface remains challenging in terms of cost and precision of operation when conventional texturing methods are used. One of the methods to create surface texture consisting of micro/nano pillars is to use the laser beam ablation. This results in hierarchical distribution of surface texture with desired pillar heights1. In addition, laser surface texturing offers significant advantages over the conventional techniques. Some of these advantages include fast processing, precision of operation, and low cost. Although the laser processing involves with high temperature processing and thermally induced stresses remain important, the defects sites can be minimized via controlling the process parameters during the texturing. Introducing the assisting gas on the texturing surface enables to generate compounds such as oxide or nitride species, which lower the surface energy considerably. Consequently, investigation of laser texturing of solar energy materials while incorporating the assisting gas becomes essential. In the present perspective, the laser surface texturing of solar energy materials for thermal power applications is presented together with challenges and future perspectives. Specifically, the followings will be presented: (1) the texture characteristics of laser treated metallic and ceramic surfaces; (2) wetting state of the textured surface, and optical properties of textured surface in terms of absorption of the solar irradiation.

Low Temperature Fabrication of Transparent Conductive Electrode With High Ultraviolet Transmittance Down to Wavelength of 250 nm

Indium tin oxide (ITO) is a broadly deployed transparent conductive electrode (TCE) with various applications in solar energy harvesting and optoelectronics. However, the low transmittance of ITO in the ultraviolet range has motivated researchers to opt for alternative materials as TCE. In this paper, the fabrication of a hybrid TCE made up of silver nanowire (AgNW) and peroxo‐constructed amorphous strontium stannate (pcaSS) is reported, employing facile spin coating solution‐processed method at 150 °C. The fabricated TCE demonstrated low sheet resistance of 32.8 Ω sq−1 and high transmittance of 88.2% at 550 nm. Furthermore, benefitting from the ultra‐high band gap of as‐synthesized pcaSS (4.5 eV), this TCE maintained its high transmittance (above 80%) inside ultraviolet range down to wavelength of 250 nm. This research contributes to the fabrication of more efficient solar energy and ultraviolet optoelectronic devices.

Ultrafast Electron Trapping and Defect-Mediated Recombination in NiO Probed by Femtosecond Extreme Ultraviolet Reflection-Absorption Spectroscopy.

Understanding the chemical nature of defect sites as well as the mechanism of defect-mediated recombination is critical for the rational design of energy conversion materials with improved efficiency. Using femtosecond extreme ultraviolet (XUV) spectroscopy in conjunction with X-ray photoelectron spectroscopy (XPS), we present results on the ultrafast electron dynamics in NiO prepared with varying concentrations of defect states. We find that oxygen vacancy defects do not serve as the primary recombination center, but rather the recombination rate scales linearly with the density of Ni metal defects. This suggests that grain boundaries between Ni metal and NiO are responsible for fast carrier recombination in partially reduced NiO. Our kinetic model shows that the photoexcited electrons self-trap via small polaron formation on the subpicosecond time scale. Additionally, we estimate an absolute measurement of small polaron formation rates, direct versus defect-mediated recombination rates, and the small polaron diffusion coefficient in NiO. This study provides important parameters for engineering NiO based materials for solar energy harvesting applications.

Multilayered Plasmonic Nanostructures for Solar Energy Harvesting

Optical properties of core-shell-shell Au@SiO2@Au nanostructures and their solar energy harvesting applications are theoretically investigated using Mie theory and heat transfer equations. The theoretical analysis associated with size-dependent modification of the bulk gold dielectric function agrees well with previous experimental results. We use the appropriate absorption cross-section to determine the solar energy absorption efficiency of the nano-heterostructures, which is strongly structure-dependent, and to predict the time-dependent temperature increase of the nanoshell solution under simulated solar irradiation. Comparisons to prior temperature measurements and theoretical evaluation of the solar power conversion efficiency are discussed to provide new insights into underlying mechanisms. Our approach would accelerate materials and structure testing in solar energy harvesting.

AgI–Ag2S heterostructures for photothermal conversion and solar energy harvesting

Abstract Heterostructures are emerging as efficient optical absorbers for photothermal therapy and solar thermal applications because of their excellent photothermal properties. In the current work, AgI–Ag2S heterostructures with enhanced and broadened optical absorption properties were prepared as photothermal materials. The synthesized AgI–Ag2S heterostructures are more efficient than the corresponding AgI and Ag2S nanopartilces and exhibit stronger absorption within the spectrum from 500 nm to 1100 nm. In comparison to the solar spectrum, the aqueous suspension containing 0.03 wt% AgI–Ag2S heterostructures delivers a solar weighted absorption (Am) value of 97.7% at a penetration distance of 1 cm, which means 97.7% solar energy has been absorbed. Under the illumination of an 808 nm laser at the power of 420 mW, the photothermal efficiency of the AgI–Ag2S heterostructures is determined to be 52%. For the solar simulation experiment, the solar thermal efficiency of the suspension is evaluated to be 97%. The results of the current work provide a solid evident that heterostructures without metal nanoparticles can also have superior photothermal properties than the corresponding single component nanoparticles. It is also evident that AgI–Ag2S heterostructures have potential applications in photothermal therapy and solar energy harvesting.

Periodically Ordered Nanoporous Perovskite Photoelectrode for Efficient Photoelectrochemical Water Splitting.

Nonmetallic materials with localized surface plasmon resonance (LSPR) have a great potential for solar energy harvesting applications. Exploring nonmetallic plasmonic materials is desirable yet challenging. Herein, an efficient nonmetallic plasmonic perovskite photoelectrode, namely, SrTiO3, with a periodically ordered nanoporous structure showing an intense LSPR in the visible light region is reported. The crystalline-core@amorphous-shell structure of the SrTiO3 photoelectrode enables a strong LSPR due to the high charge carrier density induced by oxygen vacancies in the amorphous shell. The reversible tunability in LSPR of the SrTiO3 photoelectrode was observed by oxidation/reduction treatment and incident angle adjusting. Such a nonmetallic plasmonic SrTiO3 photoelectrode displays a dramatic plasmon-enhanced photoelectrochemical water splitting performance with a photocurrent density of 170.0 μA cm-2 under visible light illumination and a maximum incident photon-to-current-conversion efficiency of 4.0% in the visible light region, which are comparable to the state-of-the-art plasmonic noble metal sensitized photoelectrodes.