Resonant and nonresonant plasmonic nanoparticle enhancement for thin-film silicon solar cells

Enhancing Silicon Solar Cell Performance Using a Thin-Film-like Aluminum Nanoparticle Surface Layer

Solar cells play an increasing role in global electricity production, and it is critical to maximize their conversion efficiency to ensure the highest possible production. The number of photons entering the absorbing layer of the solar cell plays an important role in achieving a high conversion efficiency. Metal nanoparticles supporting localized surface plasmon resonances (LSPRs) have for years been suggested for increasing light in-coupling for solar cell applications. However, most studies have focused on materials exhibiting strong LSPRs, which often come with the drawback of considerable light absorption within the solar spectrum, limiting their applications and widespread use. Recently, aluminum (Al) nanoparticles have gained increasing interest due to their tuneable LSPRs in the ultraviolet and visible regions of the spectrum. In this study, we present an ideal configuration for maximizing light in-coupling into a standard textured crystalline silicon (c-Si) solar cell by determining the optimal Al nanoparticle and anti-reflection coating (ARC) parameters. The best-case parameters increase the number of photons absorbed by up to 3.3%. We give a complete description of the dominating light-matter interaction mechanisms leading to the enhancement and reveal that the increase is due to the nanoparticles optically exhibiting both particle- and thin-film characteristics, which has not been demonstrated in earlier works.

Highly Sensitive Bimetallic-Metal Nitride SPR Biosensor for Urine Glucose Detection

The present study introduces a highly sensitive bimetallic SPR biosensor based on metal nitride for efficient urine glucose detection. Using a BK-7 prism, Au (25 nm), Ag (25nm), AlN (15 nm), and a biosample (urine) layer, the proposed sensor comprises of five layers. The selection of the sequence and dimensions of both metal layers is based on their performance in a number of case studies including both monometallic and bimetallic layers. After optimizing the bimetallic layer as Au (25 nm) - Ag (25 nm), various nitride layers were used to further increase the sensitivity by utilizing the synergistic effect of the bimetallic and metal nitride layers through case studies of several urine samples, ranging from nondiabetic to severely diabetic patients. AlN is determined to be the best suited material, and its thickness is optimized to 15 nanometers. The performance of the structure has been evaluated using a visible wavelength, i.e., λ = 633 nm, in order to increase sensitivity while providing room for low-cost prototyping. With the layer parameters optimized, a significant sensitivity of 411°/RIU (Refractive Index Unit) and figure of merit (FoM) of 105.38 /RIU has been achieved. The computed resolution of the proposed sensor is 4.17e-06. This study's findings have also been compared to some recently reported results. The proposed structure would be useful for detecting glucose concentrations, with a rapid response as measured by a substantial shift in resonance angle in SPR curves.

Broadband and Efficient Metamaterial Absorber Design Based on Gold-MgF2-Tungsten Hybrid Structure for Solar Thermal Application

We have presented a solar absorber design with gold-MgF₂-tungsten materials. The solar absorber design is optimized with nonlinear optimization mathematical method to find and optimize geometrical parameters. The wideband absorber is made of a three-layer structure composed of tungsten, magnesium fluoride, and gold. This study analyzed the absorber's performance using numerical methods over the sun wavelength range of 0.25 μm to 3 μm. The solar AM 1.5 absorption spectrum is a benchmark against which the proposed structure's absorbing characteristics are evaluated and discussed. It is necessary to analyze the behavior of the absorber under a variety of various physical parameter conditions in order to determine the results and structural dimensions that are optimal. The nonlinear parametric optimization algorithm is applied to obtain the optimized solution. This structure can absorb more than 98% of light across the near-infrared and visible light spectrums. In addition, the structure has a high absorption efficiency for the far range of the infrared spectrum and the THz range. The absorber that has been presented is versatile enough to be used in a variety of solar applications, both narrowband and broadband. The design of the solar cell that has been presented will be of assistance in designing a solar cell that has high efficiency. The proposed optimized design with optimized parameters will help design solar thermal absorbers.

Multi-octave metasurface-based refractory superabsorber enhanced by a tapered unit-cell structure

An ultra-broadband metasurface-based perfect absorber is proposed based on a periodic array of truncated cone-shaped \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {TiO}_2$$\end{document}TiO2 surrounded by TiN/\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {TiO}_2$$\end{document}TiO2 conical rings. Due to the refractory materials involved in the metasurface, the given structure can keep its structural stability at high temperatures. The proposed structure can achieve a broadband spectrum of 4.3 µm at normal incidence spanning in the range of 0.2–4.5 µm with the absorption higher than \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$90\%$$\end{document}90% and the average absorption around \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$94.71\%$$\end{document}94.71%. The absorption can be tuned through the angle of the cone. By optimizing geometrical parameters, a super absorption is triggered in the range of 0.2–3.25 µm with the absorption higher than 97.40\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}% and substantially average absorption over 99\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\%$$\end{document}%. In this regard, the proposed structure can gather more than \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$99\%$$\end{document}99% of the full spectrum of solar radiation. Furthermore, the absorption of the designed structure is almost insensitive to the launching angle up to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$50^\circ $$\end{document}50∘ for TE polarization, while it has a weak dependence on the incident angle for TM polarization. The proposed structure can be a promising candidate for thermal energy harvesting and solar absorption applications.

Towards realistic modeling of plasmonic nanostructures: a comparative study to determine the impact of optical effects on solar cell improvement

Plasmonic structures may improve cell performance in a variety of ways. More accurate determining of the optical influence, unlike ideal simulations, requires modeling closer to experimental cases. In this modeling and simulation, irregular nanostructures were chosen and divided into three groups and some modes. For each mode, different sizes of nanoparticles were randomly selected, which could result in pre-determined average particle size and standard deviation. By 3D finite-difference time-domain (3D-FDTD), the optical plasmonic properties of that mode in a solar cell structure were investigated when the nanostructure was added to the buffer/active layer of the organic solar cell. The far- and near-field results were used to compare the plasmonic behavior, relying on the material and geometry. By detailed simulations, Al and Ag nanostructure at the interface of the ZnO/active layer can improve organic solar cell performance optically, especially by the near-field effect. Unlike Au and relative Ag, the Al nanostructured sample showed less parasitic absorption loss.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10825-021-01829-x.

Performance Improvement of Triplet-Triplet Annihilation-Based Upconversion Solid Films through Plasmon-Induced Backward Scattering of Periodic Arrays of Ag and Al

The performance improvement of solid-state triplet-triplet annihilation-based photon upconversion (TTA-UC) systems is required for the application to various solar devices. The performance can be improved by making use of the local strong electric field generated through the excitation of localized surface plasmon (LSP) resonance of metal nanostructures. However, since the improvement is effective only within the limited nanospace around nanoparticles (i.e., the near-field effect), a methodology for improving the performance over a wider spatial region is desirable. In this study, a significant improvement in the threshold light excitation intensity (I_th) (77% decrease) as the figure of merit and the upconverted emission intensity (6.3 times enhancement) in a solid-state TTA-UC film with a thickness of 3 μm was achieved by stacking the film with periodic Ag half-shell arrays. The highest-enhanced upconverted emission was obtained by tuning the diffuse reflectance peak, which results from the excitation of LSP resonance of the Ag half-shell arrays, to overlap well with the photoexcitation peak of the sensitizer in the TTA-UC film. The intensity of the enhanced upconverted emission was independent of the distance between the lower edge of the TTA-UC film and the surface of half-shell arrays in the nanometer order. These results suggest that the performance improvement was attributed to the photoexcitation enhancement of the sensitizer by elongating the excitation light path length inside the TTA-UC film, which was achieved through a strong backward scattering of the incident light based on the LSP resonance excitation (i.e., the far-field effect). In addition, the upconverted emission was improved using half-shell arrays comprising low-cost Al, although the enhancement factor was 3.5, which was lower than that of Ag half-shell arrays. The lower enhancement may be attributed to a decrease in the backward scattering of the excitation light owing to the intrinsic strong interband transition of Al at long visible wavelengths.

Ultra-high sensitivity sensing based on ultraviolet plasmonic enhancements in semiconductor triangular prism meta-antenna systems

Silicon (Si), germanium (Ge), and gallium arsenide (GaAs) are familiar semiconductors that always act in the role of optical dielectrics. However, these semiconductors also have plasmonic behaviors in ultraviolet (UV) ranges due to the strong interband transitions or valence electrons. And few studies are aimed at investigating plasmonic properties in the semiconductor at the nanoscale. In this work, we discuss UV plasmonics and sensing properties in single and dimer Si, Ge, and GaAs triangular prism meta-antenna systems. The results show that obvious local surface plasmon resonances (LSPRs) can be realized in the proposed triangular prism meta-antennas, and the resonant wavelength, electromagnetic field distribution, surface charge distribution, and surface current density can be effectively tuned by structural and material parameters. In addition, we also find that the Si triangular prism meta-antenna shows more intense plasmonic responses in UV ranges than that in the Ge or GaAs triangular prism nanostructures. Especially, the phase difference between the triangular prism nanostructure and light source can effectively regulate the symbol and value of the surface charge. Moreover, the great enhancement of electric field can be seen in the dimer triangular prism meta-antennas when the distance of the gap is g<5 nm, especially g=1 nm. The most interesting result is that the maximum of refractive index sensitivity s and figure of merit (FoM) are greatly enlarged in dimer triangular prism meta-antennas. Particularly, the sensitivity can reach up to 215 nm/RIU in the dimer GaAs triangular prism meta-antennas, which is improved more than one order of magnitude. These research results may play important roles in applications of the photo detecting, plasmonic sensing and disinfecting in UV ranges.

Selective deposition of gold particles onto silicon at the nanoscale controlled by a femtosecond laser through galvanic displacement

Control of the deposition location and morphology of metals on semiconductors is of considerable importance for the fabrication of metal–semiconductor hybrid structures. For this purpose, selective nanoscale deposition of gold on silicon was successfully achieved by a two-step method in this paper. The first preparation step comprises the fabrication of ripples with a femtosecond laser. The second preparation step is to immerse the samples in a mixed aqueous solution of hydrofluoric acid (HF) and chloroauric acid (HAuCl₄). The periodically ablated ripple structures on silicon surfaces fabricated by the femtosecond laser changed the physical and chemical properties of silicon and then controlled the nucleation positions of gold nanoparticles. Gold particles tend to grow in raised positions of the ripples and no substantial growth was observed in the recesses of the ablated ripple structures. Similar phenomena were observed on the modified ripple structures; this led to the formation of periodically distributed gold sub-micron wires. Above all, this paper proposes a new mask-free method of selective metal electroless deposition that can be realized without complicated experimental equipment and tedious experimental operations.

Control of the deposition location and morphology of metals on semiconductors is of considerable importance for the fabrication of metal–semiconductor hybrid structures.

Investigation of phase transformations and corrosion resistance in Co/CoCo2O4 nanowires and their potential use as a basis for lithium-ion batteries

The paper is devoted to the study of the effect of thermal annealing on the change in the structural properties and phase composition of metal Co nanostructures, as well as the prospects of their use as anode materials for lithium-ion batteries. During the study, a four-stage phase transition in the structure of nanowires consisting of successive transformations of the structure (Со-FCC/Co-HCP) → (Со-FCС) → (Со-FCC/СоСо₂О₄) → (СоСо₂О₄), accompanied by uniform oxidation of the structure of nanowires with an increase in temperature above 400 °C. In this case, an increase in temperature to 700 °C leads to a partial destruction of the oxide layer and surface degradation of nanostructures. During life tests, it was found that the lifetime for oxide nanostructures exceeds 500 charge/discharge cycles, for the initial nanostructures and annealed at a temperature of 300 °С, the lifetimes are 297 and 411 cycles, respectively. The prospects of using Co/CoCo₂O₄ nanowires as the basis for lithium-ion batteries is shown.

Fabrication of Various Plasmonic Pt Nanostructures via Indium Assisted Solid-State Dewetting: From Small Nanoparticles to Widely Connected Networks

In this paper, the modified solid-state dewetting (MSSD) of well-defined and various uniform Pt nanostructures is demonstrated by the auxiliary diffusion enhancement. The MSSD utilizes the introduction of metallic indium (In) layers with high diffusivity in between sapphire and platinum (Pt) layer, through which the global diffusion and dewetting of metallic atoms can be significantly enhanced. Subsequently, the In atoms can be sublimated from the NP matrix, resulting in the formation of pure Pt NPs. By the systematic control of In and Pt bi-layer thickness, various areal density, size and configuration of Pt NPs are demonstrated. The In_{2 nm}/Pt_{2 nm} bilayers establish very small and highly dense NPs throughout the temperature range due to the early maturation of growth. Intermediate size of NPs is demonstrated with the In_{45 nm}/Pt_{15 nm} bilayers with the much improved interparticle spacings by annealing between 650 and 900 °C for 450 s. Finally, the In_{30 nm}/Pt_{30 nm} bilayers demonstrate the widely connected network-like nanostructures. In addition, the finite difference time domain (FDTD) simulation is employed to exploit the local electric field distributions at resonance wavelengths. The dewetting characteristics of In/Pt bilayers is systematically controlled by the modifications of layer thickness and annealing temperature and is systematically described based on the diffusion of atoms, Rayleigh instability and surface energy minimization mechanism. The optical properties demonstrate dynamic and widely tunable localized surface plasmon resonance (LSPR) responses depending upon the various surface morphologies of Pt nanostructures.

The Impact of parasitic loss on solar cells with plasmonic nano-textured rear reflectors

Significant photocurrent enhancement has been demonstrated using plasmonic light-trapping structures comprising nanostructured metallic features at the rear of the cell. These structures have conversely been identified as suffering heightened parasitic absorption into the metal at certain resonant wavelengths severely mitigating benefits of light trapping. In this study, we undertook simulations exploring the relationship between enhanced absorption into the solar cell, and parasitic losses in the metal. These simulations reveal that resonant wavelengths associated with high parasitic losses in the metal could also be associated with high absorption enhancement in the solar cell. We identify mechanisms linking these parasitic losses and absorption enhancements, but found that by ensuring correct design, the light trapping structures will have a positive impact on the overall solar cell performance. Our results clearly show that the large angle scattering provided by the plasmonic nanostructures is the reason for the enhanced absorption observed in the solar cells.

Engineered optical properties of silver-aluminum alloy nanoparticles embedded in SiON matrix for maximizing light confinement in plasmonic silicon solar cells

Self-assembled silver-aluminum (Ag-Al) alloy nanoparticles (NPs) embedded in SiO₂, Si₃N_4, and SiON dielectric thin film matrices explored as a hybrid plasmonic structure for silicon solar cells to maximize light confinement. The Ag₂Al NPs prepared by ex-vacuo solid-state dewetting, and alloy formation confirmed by X-ray diffraction and photoelectron spectroscopy analysis. Nanoindentation by atomic force microscopy revealed better surface adhesion of alloy NPs on silicon surface than Ag NPs due to the Al presence. The SiON spacer layer/Ag₂Al NPs reduced silicon average reflectance from 22.7% to 9.2% due to surface plasmonic and antireflection effects. The SiON capping layer on NPs reduced silicon reflectance from 9.2% to 3.6% in wavelength region 300–1150 nm with preferential forward light scattering due to uniform Coulombic restoring force on NPs’ surface. Minimum reflectance and parasitic absorptance from 35 nm SiON/Ag₂Al NPs/25 nm SiON structure reflected in plasmonic cell’s photocurrent enhancement from 26.27 mA/cm² (of bare cell) to 34.61 mA/cm² due to the better photon management. Quantum efficiency analysis also showed photocurrent enhancement of cell in surface plasmon resonance and off-resonance regions of NPs. We also quantified dielectric thin film antireflection and alloy NPs plasmonic effects separately in cell photocurrent enhancement apart from hybrid plasmonic structure role.

Plasmonic Solar Cells: From Rational Design to Mechanism Overview

Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. This review provides a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. The working principle is first addressed in terms of the combined effects of plasmon decay, scattering, near-field enhancement, and plasmonic energy transfer, including direct hot electron transfer and resonant energy transfer. Then, we summarize recent developments for various types of plasmonic solar cells based on silicon, dye-sensitized, organic photovoltaic, and other types of solar cells, including quantum dot and perovskite variants. We also address several issues regarding the limitations of plasmonic nanostructures, including their electrical, chemical, and physical stability, charge recombination, narrowband absorption, and high cost. Next, we propose a few potentially useful approaches that can improve the performance of plasmonic cells, such as the inclusion of graphene plasmonics, plasmon-upconversion coupling, and coupling between fluorescence resonance energy transfer and plasmon resonance energy transfer. This review is concluded with remarks on future prospects for plasmonic solar cell use.

Electrical and optical performance of plasmonic silicon solar cells based on light scattering of silver and indium nanoparticles in matrix-combination

This study demonstrates the efficacy of combining a matrix of silver nanoparticles (Ag-NPs) with indium nanoparticles (In-NPs) to improve the electric and optical performance of plasmonic silicon solar cells. We examined the excitation of localized surface plasmons of Ag-NPs and In-NPs using surface enhanced Raman scattering measurements. Optical reflectance and external quantum efficiency (EQE) measurements demonstrate that the light scattering of Ag-NPs at short wavelengths can be improved by surrounding them with In-NPs. This also leads to high EQE band matching in the high energy band of the AM1.5G solar energy spectrum. Impressive improvements in optical reflectance and EQE response were also observed at short wavelengths. Cells with a matrix of Ag-NPs (20% surface coverage) surrounded by In-NPs (80% surface coverage) increased the overall efficiency of the cell by 31.83%, as confirmed by photovoltaic current density-voltage characterization under AM 1.5 G illumination.

Ultraviolet Plasmonic Aluminium Nanoparticles for Highly Efficient Light Incoupling on Silicon Solar Cells

Plasmonic metal nanoparticles supporting localized surface plasmon resonances have attracted a great deal of interest in boosting the light absorption in solar cells. Among the various plasmonic materials, the aluminium nanoparticles recently have become a rising star due to their unique ultraviolet plasmonic resonances, low cost, earth-abundance and high compatibility with the complementary metal-oxide semiconductor (CMOS) manufacturing process. Here, we report some key factors that determine the light incoupling of aluminium nanoparticles located on the front side of silicon solar cells. We first numerically study the scattering and absorption properties of the aluminium nanoparticles and the influence of the nanoparticle shape, size, surface coverage and the spacing layer on the light incoupling using the finite difference time domain method. Then, we experimentally integrate 100-nm aluminium nanoparticles on the front side of silicon solar cells with varying silicon nitride thicknesses. This study provides the fundamental insights for designing aluminium nanoparticle-based light trapping on solar cells.

Significant light absorption enhancement in silicon thin film tandem solar cells with metallic nanoparticles

Enhancing the light absorption in microcrystalline silicon bottom cell of a silicon-based tandem solar cell for photocurrent matching holds the key to achieving the overall solar cell performance breakthroughs. Here, we present a concept for significantly improving the absorption of both subcells simultaneously by simply applying tailored metallic nanoparticles both on the top and at the rear surfaces of the solar cells. Significant light absorption enhancement as large as 56% has been achieved in the bottom subcells. More importantly the thickness of the microcrystalline layer can be reduced by 57% without compromising the optical performance of the tandem solar cell, providing a cost-effective strategy for high performance tandem solar cells.

Tunable optical response of bowtie nanoantenna arrays on thermoplastic substrates

Thermally responsive polymers present an interesting avenue for tuning the optical properties of nanomaterials on their surfaces by varying their periodicity and shape using facile processing methods. Gold bowtie nanoantenna arrays are fabricated using nanosphere lithography on prestressed polyolefin (PO), a thermoplastic polymer, and optical properties are investigated via a combination of spectroscopy and electromagnetic simulations to correlate shape evolution with optical response. Geometric features of bowtie nanoantennas evolve by annealing at temperatures between 105 °C and 135 °C by releasing the degree of prestress in PO. Due to the higher modulus of Au versus PO, compressive stress occurs on Au bowtie regions on PO, which leads to surface buckling at the two highest annealing temperatures; regions with a 5 nm gap between bowtie nanoantennas are observed and the average reduction is 75%. Reflectance spectroscopy and full-wave electromagnetic simulations both demonstrate the ability to tune the plasmon resonance wavelength with a window of approximately 90 nm in the range of annealing temperatures investigated. Surface-enhanced Raman scattering measurements demonstrate that maximum enhancement is observed as the excitation wavelength approaches the plasmon resonance of Au bowtie nanoantennas. Both the size and morphology tunability offered by PO allows for customizing optical response.

Can plasmonic Al nanoparticles improve absorption in triple junction solar cells?

Plasmonic nanoparticles located on the illuminated surface of a solar cell can perform the function of an antireflection layer, as well as a scattering layer, facilitating light-trapping. Al nanoparticles have recently been proposed to aid photocurrent enhancements in GaAs photodiodes in the wavelength region of 400-900 nm by mitigating any parasitic absorption losses. Because this spectral region corresponds to the top and middle sub-cell of a typical GaInP/GaInAs/Ge triple junction solar cell, in this work, we investigated the potential of similar periodic Al nanoparticles placed on top of a thin SiO2 spacer layer that can also serve as an antireflection coating at larger thicknesses. The particle period, diameter and the thickness of the oxide layers were optimised for the sub-cells using simulations to achieve the lowest reflection and maximum external quantum efficiencies. Our results highlight the importance of proper reference comparison, and unlike previously published results, raise doubts regarding the effectiveness of Al plasmonic nanoparticles as a suitable front-side scattering medium for broadband efficiency enhancements when compared to standard single-layer antireflection coatings. However, by embedding the nanoparticles within the dielectric layer, they have the potential to perform better than an antireflection layer and provide enhanced response from both the sub-cells.

Broadband photocurrent enhancement and light-trapping in thin film Si solar cells with periodic Al nanoparticle arrays on the front

Plasmonic resonances in metal nanoparticles are considered candidates for improved thin film Si photovoltaics. In periodic arrays the influence of collective modes can enhance the resonant properties of such arrays. We have investigated the use of periodic arrays of Al nanoparticles placed on the front of a thin film Si test solar cell. It is demonstrated that the resonances from the Al nanoparticle array causes a broadband photocurrent enhancement ranging from the ultraviolet to the infrared with respect to a reference cell. From the experimental results as well as from numerical simulations it is shown that this broadband enhancement is due to single particle resonances that give rise to light-trapping in the infrared spectral range and to collective resonances that ensure an efficient in-coupling of light in the ultraviolet-blue spectral range.

TiO2 nanoparticles induce DNA double strand breaks and cell cycle arrest in human alveolar cells

TiO2 nanoparticles (NPs) have the second highest global annual production (∼3000 tons) among the metal-containing NPs. These NPs are used as photocatalysts for bacterial disinfection, and in various other consumer products including sunscreen, food packaging, therapeutics, biosensors, surface cleaning agents, and others. Humans are exposed to these NPs during synthesis (laboratory), manufacture (industry), and use (consumer products, devices, medicines, etc.), as well as through environmental exposures (disposal). Hence, there is great concern regarding the health effects caused by exposure to NPs and, in particular, to TiO2 NPs. In the present study, the genotoxic potential of TiO2 NPs in A549 cells was examined, focusing on their potential to induce ROS, different types of DNA damage, and cell cycle arrest. We show that TiO2 NPs can induce DNA damage and a corresponding increase in micronucleus frequency, as evident from the comet and cytokinesis-block micronucleus assays. We demonstrate that DNA damage may be attributed to increased oxidative stress and ROS generation. Furthermore, genomic and proteomic analyses showed increased expression of ATM, P53, and CdC-2 and decreased expression of ATR, H2AX, and Cyclin B1 in A549 cells, suggesting induction of DNA double strand breaks. The occurrence of double strand breaks was correlated with cell cycle arrest in G2/M phase. Overall, the results indicate the potential for genotoxicity following exposure to these TiO2 NPs, suggesting that use should be carefully monitored.

Plasmonic effects in ultrathin amorphous silicon solar cells: performance improvements with Ag nanoparticles on the front, the back, and both

Thin-film hydrogenated amorphous silicon (a-Si:H) solar cells that are free-standing over a 2x2 mm area have been fabricated with thicknesses of 150 nm, 100 nm, and 60 nm. Silver nanoparticles (NPs) created on the front and/or back surfaces of the solar cells led to improvement in performance measures such as current density, overall efficiency, and external quantum efficiency. The effect of changing silver nanoparticle size and incident light angle was tested. Finite-Difference Time-Domain simulations are presented as a way to understand the experimental results as well as guide future research efforts.

Al–X and Cu–X [X = Li, Na] nano-alloys: a low cost alternative to silver and gold nanoparticles for plasmonic applications

Single X atom (X = Li and Na) is doped into Cu and Al to form Cu₁₂X and Al₁₂X clusters. The Al₁₂X clusters exhibit remarkable optical absorption properties in the range of 3–11 eV.

Self-assembled plasmonic nanoparticles on vertically aligned carbon nanotube electrodes via thermal evaporation

This study details the development of a large-area, three-dimensional (3D), plasmonic integrated electrode (PIE) system. Vertically aligned multiwalled carbon nanotube (VA-MWNT) electrodes are grown and populated with self-assembling silver nanoparticles via thermal evaporation. Due to the geometric and surface characteristics of VA-MWNTs, evaporated silver atoms form nanoparticles approximately 15-20 nm in diameter. The nanoparticles are well distributed on VA-MWNTs, with a 5-10 nm gap between particles. The size and gap of the self-assembled plasmonic nanoparticles is dependent upon both the length of the MWNT and the thickness of the evaporated silver. The wetting properties of water of the VA-MWNT electrodes change from hydrophilic (∼70°) to hydrophobic (∼120°) as a result of the evaporated silver. This effect is particularly pronounced on the VA-MWNT electrodes with a length of 1 μm, where the contact angle is altered from an initial 8° to 124°. Based on UV-visible spectroscopic analysis, plasmonic resonance of the PIE systems occurs at a wavelength of approximately 400 nm. The optical behavior was found to vary as a function of MWNT length, with the exception of MWNT with a length of 1 μm. Using our PIE systems, we were able to obtain clear surface-enhanced Raman scattering (SERS) spectra with a detection limit of ∼10 nM and an enhancement factor of ∼10(6). This PIE system shows promise for use as a novel electrode system in next-generation optoelectronics such as photovoltaics, light-emitting diodes, and solar water splitting.

Effect of experimental conditions on size control of Au nanoparticles synthesized by atmospheric microplasma electrochemistry

Atmospheric microplasma electrochemistry was utilized to synthesize Au nanoparticles (NPs). The synthesized Au NPs were investigated as a function of reduction current, solution temperature, and stirring (or not) by using ultraviolet-visible (UV-Vis) absorbance and transmission electron microscopy (TEM). It was illustrated that high current promoted the growth of Au NPs with small size, and more Au NPs with large size were synthesized as a rise of temperature. The Au NPs often with small size were synthesized as a result of stirring. The production rate, the electrostatic repulsion, and the residence time of the Au NPs at the interfacial region play an important role in the growth of Au NPs. The results shed light upon the roadmap to control the size and particle size distribution (PSD) of Au NPs synthesized by atmospheric microplasma electrochemistry.

Plasmonic ITO-free polymer solar cell

The aluminum and sliver multilayered nano-grating structure is fabricated by laser interference lithography and the intervals between nanoslits is filled with modified PEDOT:PSS. The grating structured transparent electrode functions as the anti-reflection layer which not only decreases the reflected light but also increases the absorption of the active layer. The performances of P3HT:PC₆₁BM solar cells are studied experimentally and theoretically in detail. The field intensities of the transverse magnetic (TM) and transverse electrical (TE) waves distributed in the active layer are simulated by rigorous coupled wave analysis (RCWA). The power conversion efficiency of the plasmonic ITO-free polymer solar cell can reach 3.64% which is higher than ITO based polymer solar cell with efficiency of 3.45%.

Diffractive coupling and plasmon-enhanced photocurrent generation in silicon

Arrays of metal nanoparticles are considered candidates for improved light-coupling into silicon. In periodic arrays the coherent diffractive coupling of particles can have a large impact on the resonant properties of the particles. We have investigated the photocurrent enhancement properties of Al nanoparticles placed on top of a silicon diode in periodic as well as in random arrays. The photocurrent of the periodic array sample is enhanced relative to that of the random array due to the presence of a Fano-like resonance not observed for the random array. Measurements of the photocurrent as a function of angle, reveal that the Fano-like enhancement is caused by diffractive coupling in the periodic array, which is accordingly identified as an important design parameter for plasmon-enhanced light-coupling into silicon.

Localized Surface Plasmons Enhanced Light Transmission into c-Silicon Solar Cells

The paper investigates the light incoupling into c-Si solar cells due to the excitation of localized surface plasmon resonances in periodic metallic nanoparticles by finite-difference time-domain (FDTD) technique. A significant enhancement of AM1.5G solar radiation transmission has been demonstrated by depositing nanoparticles of various metals on the upper surface of a semi-infinite Si substrate. Plasmonic nanostructures located close to the cell surface can scatter incident light efficiently into the cell. Al nanoparticles were found to be superior to Ag, Cu, and Au nanoparticles due to the improved transmission of light over almost the entire solar spectrum and, thus, can be a potential low-cost plasmonic metal for large-scale implementation of solar cells.

Self-assembled Al nanoparticles on Si and fused silica, and their application for Si solar cells

This paper presents a novel method for the self-assembly of aluminum nanoparticles on Si and fused silica. Due to high reactivity with oxygen, ex-vacuo annealing of thin deposited metal films, a method used extensively with other metals, does not work with aluminum. In the present experiment this problem was overcome by annealing the samples in-vacuo in the deposition chamber. Aluminum was thermally evaporated onto substrates at elevated temperatures (200-400 ° C) and annealed for 60 min without breaking the vacuum. It is shown that at 300 and 400 ° C the average particle size can be controlled by adjusting the amount of evaporated aluminum. Particle diameters ranging from 20 to 130 nm are demonstrated. These particles support localized surface plasmon resonances, a property that can be utilized for enhancing the efficiency of thin Si solar cells. This is explored here, and an increase in external quantum efficiency of up to 15% in a thin-film Si solar cell is demonstrated.

Self-assembled silver nanoparticles for plasmon-enhanced solar cell back reflectors: correlation between structural and optical properties

The spectra of localized surface plasmon resonances (LSPRs) in self-assembled silver nanoparticles (NPs), prepared by solid-state dewetting of thin films, are discussed in terms of their structural properties. We summarize the dependences of size and shape of NPs on the fabrication conditions with a proposed structural-phase diagram. It was found that the surface coverage distribution and the mean surface coverage (SC) size were the most appropriate statistical parameters to describe the correlation between the morphology and the optical properties of the nanostructures. The results are interpreted with theoretical predictions based on Mie theory. The broadband scattering efficiency of LSPRs in the nanostructures is discussed towards application as plasmon-enhanced back reflectors in thin-film solar cells.

X-shaped quasi-3D plasmonic nanostructure arrays for enhancing electric field and Raman scattering

We propose and demonstrate strongly enhancing electric field and Raman scattering with a large tolerance to the light incident angle and polarization by using x-shaped quasi-3D plasmonic nanostructure arrays (X-Q3D-PNAs). The finite-difference time-domain simulations were used to study the reflectance spectra and electric field profiles of X-Q3D-PNAs. Results show that both surface plasmon polaritons and localized surface plasmon polaritons (LSPPs) can be generated at the metal/dielectric interfaces of the top gold thin film with square grating x-shaped nanoholes. The resonance of the LSPPs generated at the gold islands formed between x-shaped nanoholes at the top gold thin film greatly enhance the electric fields at the tips of the cross-sectors of the x-shaped nanoholes. Both plasmon resonances and electric field enhancements are affected by the structural dimensions. The strong electric field enhancement and the large tolerance to the laser polarization were demonstrated by surface-enhanced Raman scattering experiments. This unique plasmonic property of X-Q3D-PNAs could be attractive for photovoltaics and biosensing applications.

Synthesis of Al nanoparticles: transmission electron microscopy, thermal and spectral studies

Nanoparticles of Al(0) were synthesized by solution reduction process successfully. The influence of parameters on the size of Al(0) nanoparticles were studied and the referential process parameters were obtained. The morphology and structure of the synthesized Al(0) nanoparticles were characterized by Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA), QELS Data and Infrared Spectroscopy (IR). The results show that nanoparticles of Al(0) are of high purity. XRD analysis revealed all relevant Bragg's reflection for crystal structure of Al metal. XRD spectrum also indicates there is no oxidation of Al(0) nanoparticles to aluminum oxide. TEM showed nearly uniform distribution of the particles in methanol and it was confirmed by QELS. Al(0) nanoparticles can be synthesized easily by reducing agent and are quite stable too.

Efficient optical absorption in thin-film solar cells

In order to improve the optical absorption of hydrogenated amorphous silicon (a-Si:H) thin film solar cells, a new structure consisted of ITO layer with the nonresonant nanoparticles embedded in it and a-Si:H layer, is proposed. By optimizing both the thickness of a-Si:H layer and nanoparticles size, the effects of Fabry-Perot resonance and the scattering of incident light are discussed and analyzed. It is demonstrated that the enhanced optical absorption can be achieved due to the coupling of incident light and nanostructure, simultaneously the proposed structure can be considered as gradient refractive index structure to restrain the reflection at the interface of ITO and a-Si:H thin film.

Cellular and transcriptional response of Pseudomonas stutzeri to quantum dots under aerobic and denitrifying conditions

Pseudomonas stutzeri was exposed to quantum dots (QDs) with three different surface coatings (anionic polymaleic anhydride-alt-1-octadecene (PMAO), cationic polyethylenimine (PEI), and carboxyl QDs) under both aerobic and anaerobic (denitrifying) conditions. Under aerobic conditions, toxicity (assessed per growth inhibition) increased from PMAO to carboxyl to PEI QDs. The positive charge of PEI facilitated direct contact with negatively charged bacteria, which was verified by TEM analysis. Both PMAO and PEI QDs hindered energy transduction (indicated by a decrease in cell membrane potential), and this effect was most pronounced with PEI QDs under denitrifying conditions. Up-regulation of denitrification genes (i.e., nitrate reductase narG, periplasmic nitrate reductase napB, nitrite reductase nirH, and NO reductase norB) occurred upon exposure to subinhibitory PEI QD concentrations (1 nM). Accordingly, denitrification activity (assessed per respiratory nitrate consumption in the presence of ammonia) increased during sublethal PEI QD exposure. However, cell viability (including denitrification) was hindered at 10 nM or higher PEI QD concentrations. Efflux pump genes czcB and czcC were induced by PEI QDs under denitrifying conditions, even though Cd and Se dissolution from QDs did not reach toxic levels (exposure was at pH 7 to minimize hydrolysis of QD coatings and the associated release of metal constituents). Up-regulation of the superoxide dismutase (stress) gene sodB occurred only under aerobic conditions, likely due to intracellular production of reactive oxygen species (ROS). The absence of ROS under denitrifying conditions suggests that the antibacterial activity of QDs was not due to ROS production alone. Overall, this work forewarns about unintended potential impacts to denitrification as a result of disposal and incidental releases of QDs, especially those with positively charged coatings (e.g., PEI QDs).