Solar Energy Harvesting Devices Research Articles

Taking the temperature of hot carriers

Nanophotonics Hot carriers are expected to arise in plasmonic nanostructures because of the nonradiative decay of surface plasmons. However, identifying and determining just how “hot” these carriers actually are has been challenging. Reddy et al. devised a technique that looks at the carrier transport through a single molecular junction, which effectively acts as an energy filter, and show that it can be used to determine the distribution of hot carriers in a plasmonic nanostructure (see the Perspective by Martin-Moreno). These hot carriers could be harnessed to enhance the performance of technologies, including plasmon-driven photochemistry, solar energy–harvesting devices, and efficient photodetectors. Science , this issue p. [423][1]; see also p. [375][2] [1]: /lookup/doi/10.1126/science.abb3457 [2]: /lookup/doi/10.1126/science.abc4905

Enhanced Power Conversion Efficiency via Hybrid Ligand Exchange Treatment of p-Type PbS Quantum Dots.

PbS quantum dot solar cells (QDSCs) have emerged as a promising low-cost, solution-processable solar energy harvesting device and demonstrated good air stability and potential for large-scale commercial implementation. PbS QDSCs achieved a record certified efficiency of 12% in 2018 by utilizing an n+-n-p device structure. However, the p-type layer has generally suffered from low carrier mobility due to the organic ligand 1,2-ethanedithiol (EDT) that is used to modify the quantum dot (QD) surface. The low carrier mobility of EDT naturally limits the device thickness as the carrier diffusion length is limited by the low mobility. Herein, we improve the properties of the p-type layer through a two-step hybrid organic ligand treatment. By treating the p-type layer with two types of ligands, 3-mercaptopropionic acid (MPA) and EDT, the PbS QD surface was passivated by a combination of the two ligands, resulting in an overall improvement in open-circuit voltage, fill factor, and current density, leading to an improvement in the cell efficiency from 7.0 to 10.4% for the champion device. This achievement was a result of the improved QD passivation and a reduction in the interdot distance, improving charge transport through the p-type PbS quantum dot film.

Optical, stability and energy performance of water-based MXene nanofluids in hybrid PV/thermal solar systems

Solar thermal collectors have been recognized as promising devices for solar energy harvesting. The absorbing properties of the working fluid are crucial because they can significantly influence the efficiency of the solar thermal collectors. The performance of photovoltaic-thermal (PV/T) systems can be optimized by applying nanofluids as working fluids. MXene is a newly developed 2-D nanomaterial that has proven excellent potential in electrical applications with a lack of research in the thermal and optical applications. The present work extensively studied the optical potential of the water/MXene nanofluids with respect to the variation of MXene concentrations (0.0005–0.05 wt%) and types of surfactant (CTAB or SDBS) used in a hybrid PV/T system. The relationship between the investigated parameters was evaluated through an experimental correlation. The evaluation of the nanofluids in term of the transmittance was conducted through the Rayleigh method. The MXene concentrations and the types of the surfactant play predominant role in the transmittance, absorbance and dispersion stability of the water/MXene nanofluids. The corresponding effects due to these factors become the most noticeable in the wavelengths of 300–1350 nm. Low concentration of the MXene and shorter path lengths lead to higher transmittance. The application of the low concentration of water/MXene nanofluids as the optical filtration in a hybrid PV/T system yields a higher performance compared to a conventional PV/T system. Therefore, this research work provides novelty value in understanding the impacts of using water/MXene nanofluid in the hybrid PV/T solar collectors to harness additional energy.

A plasmon-enhanced broadband absorber fabricated by black silicon with self-assembled gold nanoparticles

A lithography-free, self-assembly fabrication route exploiting black silicon (B-Si) microstructures to design a perfect absorber based on densely and disordered packed gold nanoparticles (AuNPs)-modified silicon forests have been proposed in this paper. The geometrical dimensions of microstructures were controlled by altering the flow rate of SF6/O2 in the reactive ion etching (RIE) chamber. The RIE B-Si shows a unique geometry that consists of a combination of sharp “needles” at the top and rounded “holes” at the bottom, and also shows an excellent adaptive relationship with Au deposition. By combining the light-trapping capability of the B-Si and the plasmonic nature of AuNPs in the near-infrared (NIR) range, an experimental absorption of 96.5% is achieved in a wide range from 350 to 2500 nm. This material has the potential for photonic applications, including solar energy harvesting or NIR-sensitive optoelectronic devices.

A more realistic performance evaluation of solar convertors: the need for exergic spectral analysis of radiative heat transfer

Solar energy harvesting devices have got considerable attention and significant efforts have been made to optimise their performance recently. Exergy analysis is a useful approach to evaluate the thermodynamic behaviour of the related system. However, the exergy theory of radiation is not well developed, yet. The conventional theory of Petela for radiation exergy, is not well applied for solar energy convertors which are working in a certain spectrum bandwidth such as photovoltaic (PV) panels. More specifically, the inlet exergy of PVs are generally assumed to be the full spectrum exergy, which is not the case for the available panels. In the present study, the exergy fraction functions are presented. As an application, the second law efficiency of various PV panel types are estimated based on the proposed method. It is shown that up to 55% error for exergic efficiency of PV panels might occur by using the conventional relation.

Plasmon-assisted partially reduced TiO2 nanotube arrays for photoelectrochemical water splitting

The partially reduced TiO2 nanotube arrays (R-TNTs) has been extensively investigated for photoelectrochemical (PEC) water splitting. However, the severe charge recombination and limited light harvesting hinder their photocurrent output. Herein, we present a strategy for prepared R-TNTs photoanode which can facilitate the charge separation and transfer simultaneously via formation of homojunction induced by the Ti3+ self-doping and oxygen vacancies. Additionally, we deposited plasmonic Au nanoparticles on the R-TNTs surface to extend the light absorption in visible region and accelerate the charge transfer at the solid-liquid interface via plasmonic effect. As a result, in PEC water splitting experiments, the optimized Au modified R-TNTs (Au@R-TNTs) photoanode exhibits a photocurrent density of 1.64 mA·cm−2 with solar-to-hydrogen conversion efficiency up to 0.55% under AM 1.5 G illumination, 4-fold and 2-fold higher than that of the pristine TNTs, respectively. The photocatalytic activity in the visible region was dramatically improved. The exploration of interfacial carrier dynamics in homojuntion and the investigation of the synergistic effects of plasmonic enhanced photocatalyst provides guideline for designing solar energy harvesting devices.

Efficient and Stable PbS Quantum Dot Solar Cells by Triple-Cation Perovskite Passivation.

Solution-processed quantum dots (QDs) have a high potential for fabricating low-cost, flexible, and large-scale solar energy harvesting devices. It has recently been demonstrated that hybrid devices employing a single monovalent cation perovskite solution for PbS QD surface passivation exhibit enhanced photovoltaic performance when compared to standard ligand passivation. Herein, we demonstrate that the use of a triple cation Cs0.05(MA0.17FA0.83)0.95Pb(I0.9Br0.1)3 perovskite composition for surface passivation of the quantum dots results in highly efficient solar cells, which maintain 96% of their initial performance after 1200 h shelf storage. We confirm perovskite shell formation around the PbS nanocrystals by a range of spectroscopic techniques as well as high-resolution transmission electron microscopy. We find that the triple cation shell results in a favorable energetic alignment to the core of the dot, resulting in reduced recombination due to charge confinement without limiting transport in the active layer. Consequently, photovoltaic devices fabricated via a single-step film deposition reached a maximum AM1.5G power conversion efficiency of 11.3% surpassing most previous reports of PbS solar cells employing perovskite passivation.

Broadband plasmonic absorber based on all silicon nanostructure resonators in visible region

We present a broadband plasmonic absorber (PA) based on all silicon nanostructure resonators in visible region, which can be functioned as metamaterial (MM) blackbody for nearly all light radiation. Distinct from previous designs, the proposed PA is only consisted of periodic all silicon circular-split-ring (CSR) nanostructure resonators array adhered on a continuous gold substrate. Simulation results indicate that the absorbance of the proposed PA is greater 98% from 514 THz to 638 THz, and the absorption peak is up to 99.9% at 520 THz and 626.5 THz, respectively. The proposed PA is polarization-insensitive and toleration of wide incident angles for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the designed PA can tolerate some geometric parameters errors in fabrication. Thus, the proposed PA for MM blackbody can be potential application in the photodetectors, thermal imaging, photoelectrochemical, and solar energy harvesting devices.

Graphene-based highly efficient and broadband solar absorber

We propose graphene-based solar absorber for broadband absorption response. The absorber is designed by sandwich graphene layer between the dielectric layer and resonator layer. The use of graphene layer improves the absorption in the dielectric layer. The design results in the form of absorption, reflection and normalised electric field are analysed for graphene-based design and simple design (without graphene layer). The design with the graphene layer is giving better absorption behaviour in the range of 100 THz to 1600 THz. The design results are also analysed for the different physical design parameters like gold resonator width (G_W), silver resonator width (S_W), gold dielectric layer height (G_H) and total structure width (W). The increase in the gold resonator and silver resonator width reduces the absorption and increase in height of gold dielectric layer increases the absorption. The designed structure is absorbing not only visible energy but also infrared energy and ultraviolet energy. The designed graphene-based broadband solar absorber is applicable in solar energy harvesting, light trapping and photovoltaic devices.

Computational Design of Novel Hydrogen-Doped, Oxygen-Deficient Monoclinic Zirconia with Excellent Optical Absorption and Electronic Properties

Monoclinic ZrO2 has recently emerged as a new highly efficient material for the photovoltaic and photocatalytic applications. Herein, first-principles calculations were carried out to understand how Hydrogen doping can affect the electronic structure and optical properties of the material. The effects of Hydrogen interstitial and substitutional doping at different sites and concentrations in m-ZrO2 were examined by an extensive model study to predict the best structure with the optimal properties for use in solar energy conversion devices. Hydrogen interstitials (Hi) in pristine m-ZrO2 were found to lower the formation energy but without useful effects on the electronic or optical properties. Hydrogen mono- and co-occupying oxygen vacancy (Ov) were also investigated. At low concentration of Hydrogen mono-occupying oxygen vacancy (HOv), Hydrogen atoms introduced shallow states below the conduction band minimum (CBM) and increase the dielectric constant, which could be very useful for gate dielectric application. The number and position of such defect states strongly depend on the doping sites and concentration. At high oxygen vacancy concentration, the modeled HOv-Ov structure shows the formation of shallow and localized states that are only 1.1 eV below the CBM with significantly high dielectric constant and extended optical absorption to the infrared region. This strong absorption with the high permittivity and low exciton binding energies make the material an ideal candidate for use in solar energy harvesting devices. Finally, the band edge positions of pristine and doped structures with respect to the redox potentials of water splitting indicated that Hydrogen occupying oxygen vacancies can increase the photocatalytic activity of the material for hydrogen generation due the extremely improved optical absorption and the band gap states.

Beyond Seashells: Bioinspired 2D Photonic and Photoelectronic Devices

AbstractThe discovery of novel materials that possess extraordinary optical properties are of special interest, as they inspire systems for next‐generation solar energy harvesting and conversion devices. Learning from nature has inspired the development of many photonic nanomaterials with fascinating structural colors. 2D photonic nanostructures, inspired by the attractive optical properties found on the inner surfaces of seashells, are fabricated in a facile and scalable way. The shells generate shining clusters for preying on phototactic creatures through interaction with incident solar light in water. By alternately depositing graphene and 2D ultrathin TiO2 nanosheets to form 2D–2D heterostructures and homostructures, seashell‐inspired nanomaterials with well‐controlled parameters are successfully achieved. They exhibit exceptional interlayer charge transfer properties and ultrafast in‐plane electron mobility and present fascinating nacre‐mimicking optical properties and significantly enhanced light‐response behavior when acting as photoelectrodes. A window into the fabrication of novel 2D photonic structures and devices is opened, paving the way for the design of high‐performance solar‐energy harvesting and conversion devices.

Charge Generation in Monolayer Transition Metal Dichalcogenides

At the monolayer level, many layered 2D transition metal dichalcogenides (TMDCs) are direct bandgap semiconductors in which photo-excitation creates strongly bound excitons. To incorporate these excitonic semiconductors into solar energy harvesting and conversion devices, it is critical to dissociate excitons to produce long-lived free charge carriers. There are still many open questions regarding the fundamental steps of exciton dissociation and subsequent recombination of charge carriers within 2D TMDCs. These include the roles of defects and traps in localizing charges, the types of interfaces that facilitate fast charge separation and slow recombination, and the role of charge diffusion/delocalization in overcoming the Coulomb binding energy following charge separation. In this talk, I will discuss our efforts at answering some of these questions using a number of 2D TMDC model systems and interfaces. We observe long-lived charge generation in certain neat 2D TMDCs that can be related to specific growth-related defects. Charge generation can also be enhanced by creating interfaces with the appropriate energetics for separating electrons and holes, and the lifetime of the charge-separated state is tied to the degree to which the carrier(s) can escape the interface through diffusion and/or delocalization. These studies provide insight into harnessing the potential of monolayer 2D TMDCs in solar energy harvesting and solar fuels applications.

Enhanced absorption in all-dielectric metasurfaces due to magnetic dipole excitation

All-dielectric nanophotonics lies at a forefront of nanoscience and technology as it allows to control light at the nanoscale using its electric and magnetic components. Bulk silicon does not experience any magnetic response, nevertheless, we demonstrate that the metasurface made of silicon parallelepipeds allows to excite the magnetic dipole moment leading to the broadening and enhancement of the absorption. Our investigations are underpinned by the numerical predictions and the experimental verifications. Also surprisingly we found that the resonant electric quadrupole moment leads to the enhancement of reflection. Our results can be applied for a development of absorption based devices from miniature dielectric absorbers, filters to solar cells and energy harvesting devices.

Preparation and characterization of nitrogen doped graphene oxide/nickel oxide nanocomposites for dye sensitized solar cell applications

Solar energy has become a vital type of renewable energy because of its environmental friendliness and the potential for high power conversion efficiency in solar energy harvesting devices. Dye-sensitized solar cells (DSSCs) have gained considerable interest as alternatives to the semiconductor-based thin film solar cells. Natural dye sensitized solar cells have become promising candidates for the replacement of synthetic dyes. Graphene oxide exhibited impressive photoelectric properties, large surface area, high charge-carrier mobility, high conductance and fast electron transfer. Thus graphene oxide was considered as the most promising material for various potential applications. Nickel oxides have been of particular interest because of its good electro-catalytic properties, low toxicity and low cost, which made them suitable for photo-anode in dye sensitized solar cells. In the present work, a hybrid material consisting of nickel oxide nanoparticles anchored onto the nitrogen doped graphene oxide sheets was prepared by chemical precipitation method. The structural and morphological studies of the prepared nanocomposites were investigated by X-Ray diffraction analysis and electron microscopy (FE-SEM). The presence of functional groups in the synthesized nanocomposites was studied by Fourier transform infrared spectroscopy (FT-IR). The electrochemical activity of the prepared nanocomposites was investigated by cyclic voltammetry (CV). The prepared nanocomposites were suitable for dye sensitized solar cell applications

Low‐Voltage, High‐Frequency Organic Transistors and Unipolar and Complementary Ring Oscillators on Paper

AbstractPaper substrates for flexible, mobile, and disposable electronic applications draw academic and commercial attention due to their many advantages, such as cost efficiency, low weight, mechanical flexibility, and environmental compatibility. For portable electronic applications, it is important that the electronic devices and circuits can be operated with voltages of a few volts, due to the limitations of mobile power supplies, such as solar cells or energy harvesting devices. Here, low‐voltage organic p‐channel and n‐channel transistors as well as unipolar and complementary ring oscillators are fabricated directly on the surface of a banknote. It is demonstrated that low‐power organic integrated circuits on paper substrates can be operated with supply voltages of less than 3 V and with frequencies of several hundred kilohertz. These results emphasize the prospects of organic transistors for smart paper applications.

GaAs Nanowires Grown by Catalyst Epitaxy for High Performance Photovoltaics

Photovoltaics (PVs) based on nanostructured III/V semiconductors can potentially reduce the material usage and increase the light-to-electricity conversion efficiency, which are anticipated to make a significant impact on the next-generation solar cells. In particular, GaAs nanowire (NW) is one of the most promising III/V nanomaterials for PVs due to its ideal bandgap and excellent light absorption efficiency. In order to achieve large-scale practical PV applications, further controllability in the NW growth and device fabrication is still needed for the efficiency improvement. This article reviews the recent development in GaAs NW-based PVs with an emphasis on cost-effectively synthesis of GaAs NWs, device design and corresponding performance measurement. We first discuss the available manipulated growth methods of GaAs NWs, such as the catalytic vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) epitaxial growth, followed by the catalyst-controlled engineering process, and typical crystal structure and orientation of resulted NWs. The structure-property relationships are also discussed for achieving the optimal PV performance. At the same time, important device issues are as well summarized, including the light absorption, tunnel junctions and contact configuration. Towards the end, we survey the reported performance data and make some remarks on the challenges for current nanostructured PVs. These results not only lay the ground to considerably achieve the higher efficiencies in GaAs NW-based PVs but also open up great opportunities for the future low-cost smart solar energy harvesting devices.

On the scattering directionality of a dielectric particle dimer of High Refractive Index

Low-losses and directionality effects exhibited by High Refractive Index Dielectric particles make them attractive for applications where radiation direction control is relevant. For instance, isolated metallo-dielectric core-shell particles or aggregates (dimers) of High Refractive Index Dielectric particles have been proposed for building operational switching devices. Also, the possibility of using isolated High Refractive Index Dielectric particles for optimizing solar cells performance has been explored. Here, we present experimental evidence in the microwave range, that a High Refractive Index Dielectric dimer of spherical particles is more efficient for redirecting the incident radiation in the forward direction than the isolated case. In fact, we report two spectral regions in the dipolar spectral range where the incident intensity is mostly scattered in the forward direction. They correspond to the Zero-Backward condition (also observed for isolated particles) and to a new condition, denoted as “near Zero-Backward” condition, which comes from the interaction effects between the particles. The proposed configuration has implications in solar energy harvesting devices and in radiation guiding.

Optimization of a perfect absorber multilayer structure by genetic algorithms

BackgroundAn increasing interest has been recently grown in the development of nearly perfect absorber materials for solar energy collectors and more in general for all the thermophotovoltaic applications.MethodsWide angle and broadband perfect absorbers with compact multilayer structures made of a sequence of ITO and TiN layers are here studied to develop new devices for solar thermal energy harvesting. Genetic Algorithms are introduced for searching the optimal thicknesses of the layers so to design a perfect broadband absorber in the visible range, for a wide range of angles of incidence from 0° to 50°, and for both polarizations.ResultsGenetic Algorithms allow to design several optimized structures with 6, 8, and 10 layers reaching a very high average absorbance of 97%, 99% and 99.5% respectively together with a low hemispherical total emissivity (<20%) from 200 °C till 400 °C.ConclusionsThe proposed multilayer structures use materials with high thermal stability, and high melting temperature, can be fabricated with simple thin film deposition techniques, appearing to have very promising applications in solar thermal energy harvesting.

Experimental characterization and multi-physics simulation of a triple-junction cell in a novel hybrid III:V concentrator photovoltaic–thermoelectric receiver design with secondary optical element

A lattice-matched monolithic triple-junction Concentrator Photovoltaic cell (InGa(0.495)P/GaIn(0.012)As/Ge) was electrically and thermally interfaced to a Thermoelectric Peltier module. A single optical design secondary lens was bonded to the CPV-TE receiver. The hybrid SILO-CPV-TE solar energy harvesting device was electrically, thermally and theoretically investigated. The electrical performance data for the cell under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The cell was electrically characterised under standard test conditions (1000 W/m2 irradiance, 25°C temperature and AM1.5G spectrum) for comparison with literature data. Transient multiphysics simulations in ANSYS CFX 15.0 were carried out to calculate cell temperatures and to determine the short circuit current and temperature coefficient in a scaling law. The optimization was used to determine 15 model parameters for the component sub-cells within the triple-junction cell at STC with a MATLAB scaling law. The root-mean-square error in electrical currents between measurement and simulations was 0.66%.

Tailoring of surface plasmon resonances in TiN/(Al0.72Sc0.28)N multilayers by dielectric layer thickness variation

Alternative designs of plasmonic metamaterials for applications in solar energy-harvesting devices are necessary due to pure noble metal-based nanostructures’ incompatibility with CMOS technology, limited thermal and chemical stability, and high losses in the visible spectrum. In the present study, we demonstrate the design of a material based on a multilayer architecture with systematically varying dielectric interlayer thicknesses that result in a continuous shift of surface plasmon energy. Plasmon resonance characteristics of metal/semiconductor TiN/(Al,Sc)N multilayer thin films with constant TiN and increasing (Al,Sc)N interlayer thicknesses were analyzed using aberration-corrected and monochromated scanning transmission electron microscopy-based electron energy loss spectroscopy (EELS). EEL spectrum images and line scans were systematically taken across layer interfaces and compared to spectra from the centers of the respective adjacent TiN layer. While a constant value for the TiN bulk plasmon resonance of about 2.50 eV was found, the surface plasmon resonance energy was detected to continuously decrease with increasing (Al,Sc)N interlayer thickness until 2.16 eV is reached. This effect can be understood to be the result of resonant coupling between the TiN bulk and surface plasmons across the dielectric interlayers at very low (Al,Sc)N thicknesses. That energy interval between bulk and decreasing surface plasmon resonances corresponds to wavelengths in the visible spectrum. This shows the potential of tailoring the material’s plasmonic response by controlling the (Al,Sc)N interlayer thickness, making TiN-based multilayers good prospects for plasmonic metamaterials in energy devices.