Trapping Scheme Research Articles

Embedded metal nanopatterns as a general scheme for enhanced broadband light absorption

Recently, various light trapping schemes based on inclusions of dielectric or metallic nanoparticles or nanopatterns on top of, below, or embedded within a photovoltaic (PV) absorber have been proposed to enhance the efficiency of solar cells. We demonstrate here that embedded metal nanopatterns (EMN) within the absorber layers of thin film solar cells can serve as a general scheme for broadband light absorption enhancement. The EMN scheme is compatible with a wide variety of non-crystalline solar cells, including amorphous, polycrystalline, organic, polymeric, and dye-sensitized solar cells. Simulations on the same EMN in various PV media show consistent absorption enhancement. An impedance matching model is used to explain the robustness of the effect, wherein the EMN brings the impedance of the thin-film solar cell closer to that of free space in a broadband manner, resulting in exceptional absorption enhancement in the near band gap regime. Experimental verifications are provided by Ag connecting network nanopatterns fabricated by nanosphere lithography embedded in an amorphous silicon layer, resulting in a broadband absorbance enhancement, especially in the near band gap region, in good agreement with our predictions. Connecting Ag networks with hexagonal close-packed holes are fabricated by nanosphere lithography, and then embedded into an amorphous silicon layer. For increasing embedding depth d from 5.3 to 18.4 nm, the absorbance of the structure increases, especially at the near band gap region.

An efficient light trapping scheme based on textured conductive photonic crystal back reflector for performance improvement of amorphous silicon solar cells

An efficient light trapping scheme named as textured conductive photonic crystal (TCPC) has been proposed and then applied as a back-reflector (BR) in n-i-p hydrogenated amorphous silicon (a-Si:H) solar cell. This TCPC BR combined a flat one-dimensional photonic crystal and a randomly textured surface of chemically etched ZnO:Al. Total efficiency enhancement was obtained thanks to the sufficient conductivity, high reflectivity and strong light scattering of the TCPC BR. Unwanted intrinsic losses of surface plasmon modes are avoided. An initial efficiency of 9.66% for a-Si:H solar cell was obtained with short-circuit current density of 14.74 mA/cm2, fill factor of 70.3%, and open-circuit voltage of 0.932 V.

Nanopyramids and rear-located Ag nanoparticles for broad spectrum absorption enhancement in thin-film solar cells.

Light trapping is essential to improve the performance of thin-film solar cells. In this paper, we performed a parametric optimization of nanopyramids and rear-located Ag nanoparticles that act as light trapping scheme to increase light absorption in thin-film c-Si solar cells. Our optimization reveals that the short-circuit current density in a solar cell employing only 5 μm silicon could exceed that of a standard 300 μm c-silicon wafer-based cell. Furthermore, we analyzed the underlying physics of the light absorption enhancement through the electric field intensity profiles.

Surface plasmon enhanced organic solar cell with different silver nanosphere sizes.

We have systematically investigated the plasmonic effects on the characteristics of OPV devices of a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as well as of blend of polymer poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b:3,4 b']dithioph-ene-2,6-diyl]] (PCPDTBT) and PCBM with an incorporated thin silver (Ag) film. Silver nanospheres (NSs) were introduced through a solution casting process to improve the performance of bulk-heterojunction organic solar cells. The Ag NSs with variable sizes were investigated, with the aim of optimizing the performance of devices. The power conversion efficiency (PCE) increases by a maximum 14% for the 40 nm Ag NSs. The larger-sized Ag NSs used in this study led to a larger enhancement of short circuit current JSC and PCE. Analysis of the changes in electronic performance leads to the conclusion that the plasmonic light trapping scheme improves the performance of OPV devices. This is caused by the increases of both fill factor and JSC, whilst open circuit voltage VOC remains relatively constant. These enhancements are mainly due to the localized surface plasmon resonance and light scattering of metal nanoparticles, which increase the light absorption of active layer and improve the exciton generation and dissociation.

TCO work function related transport losses at the a-Si:H/TCO-contact in SHJ solar cells

Silicon based heterojunction (SHJ) solar cells show high efficiency enabled through excellent passivation by amorphous silicon (a-Si:H), the use of light trapping schemes and transparent conductive layers. Many different research groups and companies have achieved high open-circuit voltages above 730mV, but fill factors (FFs) at the level of conventional silicon solar cells are rare. One reason for a lower FF may be the (p)a-Si:H/TCO-contact, where a Schottky diode results. This can lead to an increased transport barrier adversely affecting the hole collection and thus the FF. The role of TCOs with work functions (WF) higher (tungsten oxide (WOx)) and lower (aluminium doped zinc oxide, AZO) than the standard ITO (indium tin oxide) will be examined experimentally in this paper. The aim of this paper is the proof of concept that WF engineering can improve the contact. Schottky theory with TCO WF values taken from the literature was the main assumption for the simulations and in the case of WOx at the hole contact, it could be shown that adjusting the TCO WF to (p)-a-Si:H decreases the Schottky barrier height.

Trapping atoms using nanoscale quantum vacuum forces

Quantum vacuum forces dictate the interaction between individual atoms and dielectric surfaces at nanoscale distances. For example, their large strengths typically overwhelm externally applied forces, which makes it challenging to controllably interface cold atoms with nearby nanophotonic systems. Here we theoretically show that it is possible to tailor the vacuum forces themselves to provide strong trapping potentials. Our proposed trapping scheme takes advantage of the attractive ground-state potential and adiabatic dressing with an excited state whose potential is engineered to be resonantly enhanced and repulsive. This procedure yields a strong metastable trap, with the fraction of excited-state population scaling inversely with the quality factor of the resonance of the dielectric structure. We analyse realistic limitations to the trap lifetime and discuss possible applications that might emerge from the large trap depths and nanoscale confinement.

Hybrid light trapping structures in thin-film silicon solar cells

Enhancing light absorption in thin-film silicon solar cells is important for improving efficiency and reducing cost. We introduce a hybrid light trapping structure, where front grating and backside Ag nanoparticles are optimized for antireflection and light trapping. The solar cell with this optimized structure yields a photocurrent of 29.7 mA cm−2 within an active layer equivalent thickness of 1 μm, close to the theoretical limit. This approach is robust to various incident angles and is applicable to different thicknesses in the range of a few micrometers. Two other similar hybrid structures are also proved to be effective light trapping schemes. Moreover, we illustrate that the device implementation could be realized in low-cost technologies.

A cost-effective, community-based, mosquito-trapping scheme that captures spatial and temporal heterogeneities of malaria transmission in rural Zambia.

BackgroundMonitoring mosquito population dynamics is essential to guide selection and evaluation of malaria vector control interventions but is typically implemented by mobile, centrally-managed teams who can only visit a limited number of locations frequently enough to capture longitudinal trends. Community-based (CB) mosquito trapping schemes for parallel, continuous monitoring of multiple locations are therefore required that are practical, affordable, effective, and reliable.MethodsA CB surveillance scheme, with a monthly sampling and reporting cycle for capturing malaria vectors, using Centers for Disease Control and Prevention light traps (LT) and Ifakara Tent Traps (ITT), were conducted by trained community health workers (CHW) in 14 clusters of households immediately surrounding health facilities in rural south-east Zambia. At the end of the study, a controlled quality assurance (QA) survey was conducted by a centrally supervised expert team using human landing catch (HLC), LT and ITT to evaluate accuracy of the CB trapping data. Active surveillance of malaria parasite infection rates amongst humans was conducted by CHWs in the same clusters to determine the epidemiological relevance of these CB entomological surveys.ResultsCB-LT and CB-ITT exhibited relative sampling efficiencies of 50 and 7%, respectively, compared with QA surveys using the same traps. However, cost per sampling night was lowest for CB-LT ($13.6), followed closely by CB-ITT ($18.0), both of which were far less expensive than any QA survey (HLC: $138, LT: $289, ITT: $269). Cost per specimen of Anopheles funestus captured was lowest for CB-LT ($5.3), followed by potentially hazardous QA-HLC ($10.5) and then CB-ITT ($28.0), all of which were far more cost-effective than QA-LT ($141) and QA-ITT ($168). Time-trends of malaria diagnostic positivity (DP) followed those of An. funestus density with a one-month lag and the wide range of mean DP across clusters was closely associated with mean densities of An. funestus caught by CB-LT (P < 0.001).ConclusionsCB trapping schemes appear to be far more affordable, epidemiologically relevant and cost-effective than centrally supervised trapping schemes and may well be applicable to enhance intervention trials and even enable routine programmatic monitoring of vector population dynamics on unprecedented national scales.

Cascading metallic gratings for broadband absorption enhancement in ultrathin plasmonic solar cells

The incorporation of plasmonic nanostructures in the thin-film solar cells (TFSCs) is a promising route to harvest light into the nanoscale active layer. However, the light trapping scheme based on the plasmonic effects intrinsically presents narrow-band resonant enhancement of light absorption. Here we demonstrate that by cascading metal nanogratings with different sizes atop the TFSCs, broadband absorption enhancement can be realized by simultaneously exciting multiple localized surface plasmon resonances and inducing strong coupling between the plasmonic modes and photonic modes. As a proof of concept, we demonstrate of 66.5% in the photocurrent in an ultrathin amorphous silicon TFSC with two-dimensional cascaded gratings over the reference cell without gratings.

Manipulation and Trapping of Particles in the Ray Optics Regime Using DPS-DNG Layered Structures: Toward Calibration and Precision of Optical Tweezers

Optical traps or tweezers use the forces exerted by structured beams of light to confine and manipulate non-intrusively and non-destructively microscopic objects including living cells and bacteria, with high accuracy. This technique provides unique means to control the dynamics of small particles and played a revolutionary role in areas of the physical and biological sciences. This manuscript aims at absolute force calibration of optical beams, using new technique and structure of DPS (Double Positive index of refraction)-DNG (Double Negative index of refraction)layered structure to manipulate targets in the far filed with high resolution trapping scheme. Using this layered structure which acts as a tunable optical band-pass filter would help to calibrate and control the forces on the target(s). The band-pass effect varies with the periodic parameters of the DPS-DNG structure, applied electric and magnetic field, incidence angle and frequency.

Peristaltic transport of a Carreau fluid in a compliant rectangular duct

The study of peristaltic flow of a Carreau fluid in a compliant rectangular channel has been analyzed in this article. The assumptions of low Reynolds number and long wavelength approximation are utilized here to simplify the complicated governing equations for the three dimensional flow geometry. The resulting highly non-linear partial differential constitutive equations are solved jointly by homotopy perturbation and Eigen function expansion methods. The effects of various physical parameters on velocity distribution have been observed graphically for both two and three dimensional aspects. The trapping scheme has also been discussed by plotting stream lines.

Lambertian light trapping in thin crystalline macroporous Si layers

AbstractLambertian light trapping is a benchmark for efficient light trapping. In this Letter we experimentally quantify the degree of Lambertian light trapping in a macroporous silicon layer. The optical absorption of the effective (26.7 ± 5.5) µm thick sample with randomly arranged pores yields a photogeneration corresponding to a maximum current density of (40.8 ± 0.4) mA cm–2 and thus achieves a fraction of 0.985 ± 0.012 of the current density expected from a Lambertian light trapping scheme. The measured spectrum of the escape reflectance is well described with an analytic model assuming a complete randomization of the directions of light propagation. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Nanofiber-based atom trap created by combining fictitious and real magnetic fields

We propose a trap for cold neutral atoms using a fictitious magnetic field induced by a nanofiber-guided light field in conjunction with an external magnetic bias field. In close analogy to magnetic side-guide wire traps realized with current-carrying wires, a trapping potential can be formed when applying a homogeneous magnetic bias field perpendicular to the fiber axis. We discuss this scheme in detail for laser-cooled cesium atoms and find trap depths and trap frequencies comparable to the two-color nanofiber-based trapping scheme but with one order of magnitude lower power of the trapping laser field. Moreover, the proposed scheme allows one to bring the atoms closer to the nanofiber surface, thereby enabling efficient optical interfacing of the atoms with additional light fields. Specifically, optical depths per atom, σ0/Aeff, of more than 0.4 are predicted, making this system eligible for nanofiber-based nonlinear and quantum optics experiments.

Ehrenfest dynamics and frictionless cooling methods

Recently introduced methods which result in shortcuts to adiabaticity, particularly in the context of frictionless cooling, are rederived and discussed in the framework of an approach based on Ehrenfest dynamics. This construction provides physical insights into the emergence of the Ermakov equation, the choice of its boundary conditions, and the use of minimum uncertainty states as indicators of the efficiency of the procedure. Additionally, it facilitates the extension of frictionless cooling to more general situations of physical relevance, such as optical dipole trapping schemes. In this context, we discuss frictionless cooling in the short-time limit, a complementary case to the one considered in the literature, making explicit the limitations intrinsic to the technique when the full three-dimensional case is analyzed.

Imprinted Electrodes for Enhanced Light Trapping in Solution Processed Solar Cells

A simple approach is demonstrated to combine a light trapping scheme and a conductive substrate for solution processed solar cells. By means of soft lithography, a new light-trapping architecture can be integrated as the bottom electrode for emerging thin-film solar-cell technologies without added costs, fully compatible with low-temperature processes, and yielding an enhancement in the photocurrent without altering the rest of the electrical performance of the device.

Demonstration of enhanced absorption in thin film Si solar cells with periodic microhemisphere hole arrays

This paper reports a study about how to enhance the performance of thin film Si solar cells. Periodic microhemisphere hole (PMHH) arrays with a period of 10μm and a depth of ~4μm were made on the glass wafers. We found that the PMHH arrays can trap light via testing the transmittance of glass with PMHH arrays. Comparing with the original cell, the thin film Si solar cell covered by this kind of PMHH arrays glass is different from the following two perspectives: the short-circuit current (Jsc) increased by 7.5% and the conversion efficiency (Eff) enhanced by 5.2%. The design based on light trapping scheme on the external of cell is feasible and worth promoting.

Potential of high-mobility sputtered zinc oxide as front contact for high efficiency thin film silicon solar cells

For thin film silicon solar cells with high conversion efficiency and low production costs transparent conducting oxide (TCO) substrates with a high performance are required. TCO layers must have excellent conductivity and high transparency over a wide range in the VIS/NIR wavelength spectrum. Moreover, an advanced light trapping scheme has to be implemented, generally obtained by TCO surface texture. For low production costs it is favorable to keep the TCO and silicon layers as thin as possible. We present methods that accomplish all of these requirements. Tandem solar based on amorphous and microcrystalline silicon deposited on DC magnetron-sputtered zinc oxide (ZnO:Al) coated substrates, which have been capped with silicon and subsequently annealed at 500°C, result in an efficiency improved by 0.4% reaching 12.4%. This is due to the increased carrier mobility, reaching up to 70cm2/Vs, and improved transparency of the ZnO:Al. The high TCO conductivity allows for reducing the layer thickness significantly. In order to demonstrate the potential of combining this improved TCO with alternative light scattering concepts, we show results of a tandem cell on substrates comprising ZnO:Al sputtered on sol–gel coated light-scattering layers with dielectric particles having excellent light trapping properties. Combining both methods will allow for thin film silicon solar cells with high efficiency and potentially low production costs.

Advanced light trapping designs for high efficiency thin film silicon solar cells

Abstract State-of-the-art optical trapping designs for tandem thin film silicon solar cells in the superstrate configuration commonly feature two elements: a textured transparent conductive oxide front contact and a low refractive index interlayer between top and bottom cell. We investigate more advanced super light trapping schemes that have been designed and implemented in thin film tandem junctions at different levels in the solar cells to further enhance light trapping capabilities. Regularly patterned nano-imprinted substrates offer an additional capability to tune the substrate morphology and optimize it for enhanced solar cell performance. We show that the onset of defect formation in thin film layers can be controlled and that the spectral response in the infra-red part of the spectrum is increased. Intermediate reflectors with ultra-low refractive indeces and plasmonic properties lead to increased light confinement in top cells. Results show that reducing the refractive index below 1.5 still leads to a substantial current increase in the top cell. These innovative designs improve the output current in amorphous/microcrystalline tandem devices with thin photo-active layers. In addition, they surprisingly enhance the electrical parameters of the tandem cells with a record open circuit voltage of 1.47 V. Plasmonic effects of metal nano-particles embedded in interlayers do not compromise the electrical solar cell parameters and similarly strengthen light confinement in the top cell, however detrimental effects are observed in the bottom cell current output.

Spectroscopy, manipulation and trapping of neutral atoms, molecules, and other particles using optical nanofibers: a review.

The use of tapered optical fibers, i.e., optical nanofibers, for spectroscopy and the detection of small numbers of particles, such as neutral atoms or molecules, has been gaining interest in recent years. In this review, we briefly introduce the optical nanofiber, its fabrication, and optical mode propagation within. We discuss recent progress on the integration of optical nanofibers into laser-cooled atom and vapor systems, paying particular attention to spectroscopy, cold atom cloud characterization, and optical trapping schemes. Next, a natural extension of this work to molecules is introduced. Finally, we consider several alternatives to optical nanofibers that display some advantages for specific applications.

A theoretical study of Prandtl nanofluid in a rectangular duct through peristaltic transport

In the current study, peristaltic transport of Prandtl nanofluid is investigated in a uniform rectangular duct. Interaction of peristaltic flow of non-Newtonian fluid model with nano particles is investigated under the long wave length and low Reynolds number approximations. The governing equations are solved by homotopy perturbation method to get the convergent series solution. Effects of all emerging physical parameters are demonstrated with the help of graphs for temperature distribution, nano particles concentration, pressure rise and pressure gradient. Trapping scheme is also described through streamlines.