Materials For Solar Energy Harvesting Research Articles

Highly efficient molybdenum nanostructures for solar thermophotovoltaic systems: One-step fabrication of absorber and design of selective emitter

Efficient solar energy harvesting materials or structures have become a topic of great interest in response to the ever-increasing energy demand. Refractory transition metals have been found to exhibit attractive properties in broadband absorptance, making them highly effective in solar thermophotovoltaic (STPV) systems that aim to surpass the Shockley-Queisser limit. Typically, broadband absorbers are made from hybrid materials or complex geometrical structures, which require multi-step fabrication technologies. In this study, we successfully developed a highly efficient broadband absorber based on molybdenum (Mo) nanosheets using a one-step physical vapor deposition process. The nanosheets result in the high absorber efficiencies of 96.1 % for blackbody radiation (BBR) at 5778 K and of 96.4 % for air mass (AM) 1.5 spectrum, and are insensitive to polarization and incident angle. After annealing at 1650 K for 24 h, the Mo nanosheets absorber demonstrates outstanding thermal stability without compromising the efficiency of the STPV system. To complete the STPV system, a selective narrowband Mo-based gratings emitter was further designed with a high emissivity of 96 % at a wavelength of 2.17 μm, resulting in a high PV cell efficiency of 41.8 % around 1723 K. Through a series of theoretical calculations, the proposed STPV system can achieve an overall conversion efficiency of 40.2 % by a trade-off between the structure temperature and the sun concentration. Furthermore, an efficiency of 35.5 % can be achieved at a low temperature of 1073 K with a low solar concentration of 500 suns.The results provide tremendous opportunities for widespread applications of high-performance STPV systems.

Introduction to emerging materials for solar energy harvesting

Guest Editors Joel M. R. Tan, Frank E. Osterloh, and Lydia Wong introduce this Journal of Materials Chemistry A themed collection on emerging materials for solar energy harvesting.

Influence of atmospheric conditions on the formation and structural properties of two-dimensional SbSI films

Two-dimensional heavy pnictogen chalcohalides, such as SbSI, SbSeI, and BiSI, are promising materials for solar energy harvesting (SEH) devices. In this paper, we report the influence of atmospheric conditions on the formation and structural properties of SbSI films fabricated under N2 and air atmospheres using a modified two-step method. Under N2 atmosphere, a preferentially (121)-oriented SbSI film without impurities formed. In contrast, under air atmosphere, a film with mixed crystalline phases of SbSI and secondary Sb2O3 formed. The Sb2O3 phase could be reduced by applying excess sulfur. These results provide a fundamental step toward optimizing the properties of chalcohalides for SEH device applications.

Photo-thermal conversion properties of Cr, Mo, and W nanofluids in polyethylene glycol prepared by laser ablation in liquid method for direct absorption solar collectors applications

Nanofluids (NFs) are promising materials for solar-energy harvesting. The main drawback of NFs is their instability and longtime preparation methods that the purpose of this work relies on overcoming these problems. The Cr, Mo, and W NFs in polyethylene glycol (PEG) were synthesized by laser ablation in liquid (LAL). The capability of the prepared NFs in photo-thermal conversion was investigated under 60 min solar simulator irradiation at 1 Sun and thermo-physical properties of them (SER, Etotal, E%, and B) were calculated, indicating Cr NF has the highest photo-thermal conversion efficiency (E%≅85% at its near-to-surface). The comparison of nanoparticles radius obtained with transmission electron microscopy (TEM) and the hydrodynamic radius obtained with dynamic light scattering (DLS) methods, reveals that nanoparticles were surrounded by a thick layer of PEG molecules, leading to the super-stable and long-life NFs. The effect of the nanoparticle concentration, light intensity, and consecutive heating–cooling cycles on the performance of NFs was investigated. Under 1 h sunlight illumination (∼850–960 W/m2 intensity), the surface temperature of Cr NF reaches ≅ 65 ℃, indicating the Cr NF is highly eligible for photo-thermal conversion in the real outdoor condition. The low cost and simplicity of the synthesis method, no need to use stabilizer, super durability, high-thermal stability, low rate constant of heat dissipation, and high photo-thermal conversion efficiency confirms that Cr/PEG NF can be used as potential working fluid for direct absorption solar collectors (DASCs).

Non-Covalent Assembly of Multiple Fluorophores in Edible Protein/Lipid Hydrogels for Applications in Multi-Step Light Harvesting and White-Light Emission.

The design and production of biodegradable and sustainable non-toxic materials for solar-energy harvesting and conversion is a significant challenge. Here, our goal was to report the preparation of novel protein/lipid hydrogels and demonstrate their utility in two orthogonal fundamental studies-light harvesting and white-light emission. Our hydrogels contained up to 90% water, while also being self-standing and injectable with a syringe. In one application, we loaded these hydrogels with suitable organic donor-acceptor dyes and demonstrated the energy-transfer cascade among four different dyes, with the most red-emitting dye as the energy destination. We hypothesized that the dyes were embedded in the protein/lipid phase away from the water pools as monomeric entities and that the excitation of any of the four dyes resulted in intense emission from the lowest-energy acceptor. In contrast to the energy-transfer cascade, we demonstrate the use of these gels to form a white-light-emitting hydrogel dye assembly, in which excitation migration is severely constrained. By restricting the dye-to-dye energy transfer, the blue, green, and red dyes emit at their respective wavelengths, thereby producing the composite white-light emission. The CIE color coordinates of the emission were 0.336 and 0.339-nearly pure white-light emission. Thus, two related studies with opposite requirements could be accommodated in the same hydrogel, which was made from edible ingredients by a simple method. These gels are biodegradable when released into the environment, sustainable, and may be of interest for energy applications.

Lead immobilization for environmentally sustainable perovskite solar cells.

Lead halide perovskites are promising semiconducting materials for solar energy harvesting. However, the presence of heavy-metal lead ions is problematic when considering potential harmful leakage into the environment from broken cells and also from a public acceptance point of view. Moreover, strict legislation on the use oflead around the world has driven innovation in the development of strategies for recycling end-of-life products by means of environmentally friendly and cost-effective routes. Lead immobilization is a strategy to transform water-soluble lead ions into insoluble, nonbioavailable and nontransportable forms over large pH and temperature ranges and tosuppress lead leakage if the devices are damaged. An ideal methodology should ensure sufficient lead-chelating capability without substantially influencing the device performance, production cost and recycling. Here we analyse chemical approaches to immobilize Pb2+ from perovskite solar cells, such as grain isolation, lead complexation, structure integration and adsorption of leaked lead, based on their feasibility to suppress lead leakage to a minimal level. We highlight the need for a standard lead-leakage test and related mathematical model to be established for the reliable evaluation of the potential environmental risk of perovskite optoelectronics.

Easily Repairable and High-Performance Carbon Nanostructure Absorber for Solar Photothermoelectric Conversion and Photothermal Water Evaporation

Carbon materials are a category of broadband solar energy harvesting materials that can convert solar energy into heat under irradiation, which can be used for photothermal water evaporation and photothermoelectric power generation. However, destruction of the carbon nanostructure during usage will significantly decrease the light-trapping performance and, thus, limit their practical applications. In this article, an easily repairable carbon nanostructure absorber with full-solar-spectrum absorption and a hierarchically porous structure is prepared. The carbon absorber shows a superhigh light absorption of above 97% across the whole solar spectrum because of multiple scatterings within the carbon nanostructure and photon interaction with the carbon nanoparticles. The excellent light absorption performance directly leads to a good photothermal effect. As a consequence, the carbon absorber integrated with a thermoelectric module can obtain a large power (133.3 μW cm-2) output under 1 sun. In addition, the carbon absorber combined with the sponge can achieve a high photothermal water evaporation efficiency of 83.6% under 1 sun. Its high-efficiency solar-to-electricity and photothermal water evaporation capabilities demonstrate that the carbon absorber with superhigh absorption, simple fabrication, and facile repairability shows great potential for practical fresh water production and electric power generation.

Light harvesting hexamolybdenum cluster integrated with the 3D ordered semiconductor inverse opals for optoelectronic property

Solar energy-harvesting materials have significantly contributed to the development of energy-saving applications for several decades. We have mainly used a new concept composed of the electrophoretic deposition technique and photonic crystal structural engineering to understand the tunable light-absorption and electronic conduction properties. A hexamolybdenum cluster compound (denoted as the Mo6 cluster) was successfully functionalized on a tin pyrophosphate semiconductor integrated within an inverse opal photonic crystal. The size of the periodical pores, surface modification, and chemical composition of the infiltration material of the inverse opal film have been investigated to control the photonic bandgap in the visible range and the efficiency of the deposited Mo6 cluster. The photoactive Mo6 clusters act as a visible light harvester and generate an efficient photo-induced current upon light absorption that is enhanced by a slow photon effect occurring at the photonic stopband edges. The electron and proton are transferred in the inorganic-organic network via hydrogen bonds by a hopping mechanism to generate a rapid photoconductivity response during light irradiation. Specific attention focused on the role of humidity and temperature regarding the reproducibility of the experiments and the photosensitivity of the nanocomposite. The suitable tunable photo-induced conduction property in organic-inorganic materials opens a new opportunity for the applicability of cluster-based compounds in visible optoelectronic devices.

Using Photonic Glasses as Colored Covers for Solar Energy Harvesting

AbstractThe increasing demand for renewable energy is promoting technologies that integrate solar energy harvesting materials with the human living environment, such as building‐integrated photovoltaics. This places requirements on developing colored covers with a trade‐off between efficiency and aesthetics, providing a new stage for the large‐scale application of structural color technologies. This study investigates the theoretic feasibility of employing the photonic glass, a random packing of monodisperse dielectric microspheres, as the colored cover for solar energy harvesting. Based on numerous optical simulations, the color and average solar transmissivity of the photonic glasses with varying parameters are evaluated. Results show that using non‐absorbing microspheres with relatively high refractive index, about 3 µm thick photonic glasses can enable colors with lightness over 50 while keeping average solar transmissivity over 80%. Due to the short‐range structural correlation, it is demonstrated that photonic glasses can generate purple, blue, cyan, light green, and gray colors, but cannot help with yellow and red hues. Finally, the effects of several enhancement methods are clarified, and possible ways for expanding the color range are demonstrated. These results provide a comprehensive guide to the practical implementations of structural color using photonic glasses, particularly in the colorization of solar energy materials.

Donor-acceptor carbazole-based conjugated microporous polymers as photocatalysts for visible-light-driven H2 and O2 evolution from water splitting

Although novel donor–acceptor conjugated microporous polymers (D-A CMPs) that absorb visible light broadly and allow the efficient isolation of photoinduced electrons and holes are being sought for water splitting photocatalysis, their elusive energy band structures have made it a challenge to produce both H2 and O2 simultaneously. In this paper, for the first time, we develop a series of semiconducting D-A CMPs with various sulfur and nitrogen contents and degrees of conjugation for effective photocatalytic H2 and O2 generation from water. Here, we used a carbazole (Cz) moiety as the donor, and pyrene (Py), triphenyltriazine (TPT), benzothiadiazole (BT), and thiazolylthiazole (TzTz) as the acceptors. The resulting D-A CMPs had large surface areas (up to 1530 m2 g–1) and high thermal stabilities (Td10: up to 623 °C; char yield: up to 83 wt%). Moreover, the Cz-TzTz CMP provided an excellent hydrogen evolution rate (HER), reaching 15.3 mmol g–1 h–1 in the presence of ascorbic acid as the sacrificial electron donor, but without the need for an additional Pt co-catalyst. Interestingly, the Cz-TPT CMP provided an excellent oxygen evolution rate (OER) of 3.38 mmol g–1 h–1 when using AgNO3 as a sacrificial electron acceptor; this value is competitive with those of most previously reported organic photocatalysts. These highly active CMP-based photocatalysts appear to be useful materials for solar energy harvesting and conversion.

Relative straggle of sputtering parameters as a potential measure of power conversion efficiency of Perovskite materials

The growing demand for electricity necessitates the development of time-efficient computational methods in search of better solar energy-harvesting materials. One challenge has been ways to improve the power conversion efficiencies (PCEs) of potential harvesters.In this paper, an ion sputtering approach was used to study the problem of estimation of the power conversion efficiencies (PCEs) of perovskite solar device materials through their surface sputtering signatures. This rests on a hypothesis that the similarity between the phenomenon of photon excitation from light-sensitive absorbers, leading to electricity generation, and ejection of energetic particles from sputtered surfaces, could be exploited to estimate PCE. Hence, a Monte Carlo (MC) simulation of the sputtering of surfaces of perovskite materials with energetic ions was performed; and a number of quantities that could be used for the estimation of PCE were calculated. The results indicated that the relative straggle of surface sputtering parameters of the materials could be an effective measure of the theoretical maximum power conversion efficiencies of these materials. In particular, the relative straggle of the projected range of the ions in the respective materials was found to be close to reported experimental results of PCEs in the literature.

MXene-Based Materials for Solar Cell Applications

MXenes are a class of two-dimensional nanomaterials with exceptional tailor-made properties, making them promising candidates for a wide variety of critical applications from energy systems, optics, electromagnetic interference shielding to those advanced sensors, and medical devices. Owing to its mechano-ceramic nature, MXenes have superior thermal, mechanical, and electrical properties. Recently, MXene-based materials are being extensively explored for solar cell applications wherein materials with superior sustainability, performance, and efficiency have been developed in demand to reduce the manufacturing cost of the present solar cell materials as well as enhance the productivity, efficiency, and performance of the MXene-based materials for solar energy harvesting. It is aimed in this review to study those MXenes employed in solar technologies, and in terms of the layout of the current paper, those 2D materials candidates used in solar cell applications are briefly reviewed and discussed, and then the fabrication methods are introduced. The key synthesis methods of MXenes, as well as the electrical, optical, and thermoelectric properties, are explained before those research efforts studying MXenes in solar cell materials are comprehensively discussed. It is believed that the use of MXene in solar technologies is in its infancy stage and many research efforts are yet to be performed on the current pitfalls to fill the existing voids.

Aspect ratio dependent air stability of PbSe nanorods and photovoltaic applications.

Development of unique strategies to overcome Shockley–Queisser (SQ) limit in solar cells has gained a great deal of interest. Multiple exciton generation (MEG) process has been considered as one of the best approaches to the SQ limitation. In this respect, PbSe quantum dots (QDs) and nanorods (NRs) have been regarded as promising solar energy harvesting materials owing to their noticeable MEG yields. Although air stability has been regarded as one of the main disadvantage of PbSe QDs, no study has pointed out to the air sensitivity of PbSe NRs yet. Here, we reveal the effect of aspect ratio on air sensitivity and optical properties of PbSe NRs and discover that NRs with higher aspect ratios are more air stable, attributed to the reduced density of NR ends with air sensitive {100} facets. Furthermore, a band offset was created by utilization of tetrabutylammonium iodide and 1,2-ethanedithiol ligands in cell designs. We found that solar cells based on pristine PbSe NRs are limited by low open circuit voltages due to leakage current pathways. On the other hand, modified cells comprising light absorbing layers prepared by blending NRs and QDs and hole transporting QD layer exhibit a 10-fold improvement in solar cell efficiency.

High‐Efficiency Photothermal Water Evaporation using Broadband Solar Energy Harvesting by Ultrablack Silicon Structures

Development of broadband absorption materials for solar energy harvesting is an important strategy to address global energy issues. Herein, it is demonstrated that an ultrablack silicon structure with abundant surface texturing can absorb about 98.7% solar light within the wavelength range of 300 to 2500 nm, i.e., a very large range and amount. Under 1 sun irradiation, the ultrablack silicon sample's surface temperature can increase from 21.2 to 51.2 °C in 15 min. During the photothermal water evaporation process, the ultrablack silicon sample's surface temperature can still reach a highest temperature of 43.2 °C. The average photothermal conversion efficiency (PTCE) can be as high as 72.96%. The excellent photothermal performance to the excellent light‐trapping ability of the pyramidal surface nanostructures during solar illumination, which leads to extremely efficient absorption of light, is attributed. In addition, the large water contact area also enables fast vapor transport. The stability of the photothermal converter is also examined, presenting excellent structure and performance stabilities over 10 cycles. This indicates that the ultrablack Si absorber can be a promising photothermal conversion material for seawater desalination, water purification, photothermal therapy, and more.

Co and Ni assisted CdS@g-C3N4 nanohybrid: A photocatalytic system for efficient hydrogen evolution reaction

Although the green production of H2 through water splitting has prompted the search for solar energy harvesting materials, this still remains an ongoing challenge in the field. We report here a novel and cost-effective photocatalytic system, Co and Ni assisted CdS-NRs/g-C3N4 nanohybrid, with the potential to significantly accelerate the solar-assisted water-splitting reaction. In this system, the co-catalysts (Co and Ni) are selectively incorporated as redox mediators to impart electrons and holes away from CdS-NRs/g-C3N4. As a result, an excellent H2 production rate of 11376 μmol g−1h−1, turnover number (TON) of 1945 (after 24 h), and external quantum yield (EQY) of 4.4% were obtained at 420 nm and under mild reaction conditions. In addition, when the reaction media was tested in the absence of co-catalysts, a notable decrease in activity was observed indicating the promising role of Ni and Co as cocatalysts. The process of redox shuttle proceeds without adding sacrificial reagents, and relies entirely on the employed cocatalysts to competently separate the oxidation and reduction steps. It is anticipated that this unique cocatalysts-supported nanohybrid can create a synergistic effect between the cocatalysts and the CdS-NRs/g-C3N4 heterojunction, providing more active sites to the catalytic system for the subsequent water splitting redox reaction. The experimental results reveal that the selective and optimum use of dual cocatalysts can be a promising approach to trigger both the production of H2 and improve the stability of the photocatalytic system for overall water splitting.

Enhanced Photovoltaic and Photosensing Performances in Gadolinium-Doped Bismuth Ferrite

Recent emerging developments have demonstrated that bismuth ferrite is one of the promising lead-free perovskite materials for solar-energy harvesting, photoelectrochemical conversion, and photodetector. This work reports high short-circuit photocurrent densities ~1.2×1033 µA/cm2 in p-type gadolinium (Gd)-doped BiFeO3 ceramic with n-type indium-tin-oxide under 405 nm irradiation and sunlight at 102 mW/cm2 intensity, respectively. A polarization-enhanced photosensing responsivity (R) of ~5.4×10-2 A/W and detectivity (D*) of ~1.5×1011 Jones were achieved at low 405 nm irradiation. Enhanced photovoltaic conversion via a prior electric-field poling can be attributed to the p-n junction and field-modulated Schottky barrier in conjunction with domain nucleation, ordered polar nano-regions (PNRs), and increased O 2p-Fe 3d orbital hybridization. The network of domain walls and grain boundaries serves as conduction pathways for the photo-generated charge carriers. The remarkable improvement of photocurrent in polycrystalline Gd-doped BiFeO3 opens a window for using bismuth ferrite materials in self-powered UV-visible photodetector.

Highly active composite TiO2-polypyrrole nanostructures for water and air depollution under visible light irradiation

Abstract Engineering photocatalytic materials for solar energy harvesting and environmental remediation is a very promising prospect to solve energy and environment issues. Here we report the preparation of a nanocomposite formed by TiO2 with nanostructured polypyrrole (PPyNS-TiO2) and its photocatalytic properties. We show that this nanocomposite is very active for water and air treatment under UV and visible light irradiation. This activity is higher than that of bare TiO2 and PPyNS, and much improved compared to that of TiO2-bulk polypyrrole (PPybulk-TiO2). The nanostructuration of the conjugated polymer is a key factor for the photocatalytic activity of the composite. The large enhancement of the photocatalytic activity is ascribed to the heterojunction between PPyNS and TiO2, which broadens the absorption of visible light and facilitates the charge carriers’ separation. These results foresee the composite PPyNS-TiO2 photocatalyst for water and air purification in environment remediation.

Using Deep Machine Learning to Understand the Physical Performance Bottlenecks in Novel Thin‐Film Solar Cells

AbstractThere is currently a worldwide effort to develop materials for solar energy harvesting which are efficient and cost effective, and do not emit significant levels of CO2 during manufacture. When a researcher fabricates a novel device from a novel material system, it often takes many weeks of experimental effort and data analysis to understand why any given device/material combination produces an efficient or poorly optimized cell. It therefore takes the community tens of years to transform a promising material system to a fully optimized cell ready for production (perovskites are a contemporary example). Herein, developed is a new and rapid approach to understanding device/material performance, which uses a combination of machine learning, device modeling, and experiment. Providing a set of electrical device parameters (charge carrier mobilities, recombination rates, trap densities, etc.) in a matter of seconds thus offers a fast way to directly link fabrication conditions to device/material performance, pointing a way to further and more rapid optimization of light harvesting devices. The method is demonstrated by using it to understand annealing temperature and surfactant choice and in terms of charge carrier dynamics in organic solar cells made from the P3HT:PCBM, PBTZT‐stat‐BDTT‐8:PCBM, and PTB7:PCBM material systems.

Crystal Engineering: An Outlook for the Future

Crystal Engineering has traditionally dealt with molecular crystals. It is the understanding of intermolecular interactions in the context of crystal packing and in the utilization of such understanding in the design of new solids with desired physical and chemical properties. We outline here five areas which come under the umbrella of Crystal Engineering and where we feel that a proper planning of research efforts could lead to higher dividends for science together with greater returns for humankind. We touch on themes and domains where science funding and translation efforts could be directed in the current climate of a society that increasingly expects applications and utility products from science and technology. The five topics are: 1) pharmaceutical solids; 2) industrial solid state reactions; 3) mechanical properties with practical applications; 4) MOFs and COFs framework solids; 5) new materials for solar energy harvesting and advanced polymers.

Tuning the electronic structure of GeC/WS2 van der Waals heterostructure by electric field and strain: A first principles study

Van der Waals (vdW) heterostructures made by stacking two-dimensional (2D) materials, open up a wide landscape of possibilities in bandgap engineering, due to the distinct properties of the building layers and diverse stacking arrangements possible. In this work, ab initio calculations based on density functional theory were performed to systematically investigate the tuning of electronic properties of GeC/WS2 heterostructures by applying either a vertical external electric field or a biaxial strain. GeC/WS2 heterostructures exhibit a direct band gap and a type-II vdW heterostructure. The bandgap of GeC/WS2 heterostructure can be dramatically modulated by applying a vertical external electric field or a biaxial strain, and semiconductor-metal transitions are observed under high electric field and large strain. The change of band gap is due to the shift of band edges of the heterostructure due to the static electric field induced potential energy and strain induced deformation potential. Differences in the pattern of change style can be assigned to changes of the bands assigned to CBM and VBM. It is interesting to note that the shift of band edge by electric field is screened by a factor of 3.54 as compared to the electrostatic calculation. The deformation potential of the CBM consisted of W 5d orbital is −1.58 eV, and that of the VBM consisted of C 2p orbital is −0.01 eV. In addition, the optical properties of the heterostructure exhibit a significant enhancement compared to the constituent layers, which indicates improved light absorption. The above results suggest that GeC/WS2 vdW heterostructures can find applications as opto-electronic devices and efficient solar energy harvesting materials.