Light trapping characteristics of glass substrate with hemisphere pit arrays in thin film Si solar cells

In this paper, the light trapping characteristics of glass substrate with hemisphere pit （HP） arrays in thin film Si solar cells are theoretically studied via a numerical approach. It is found that the HP glass substrate has good antireflection properties. Its surface reflectance can be reduced by - 50% compared with planar glass. The HP arrays can make the unabsorbed light return to the absorbing layer of solar cells, and the ratio of second absorption approximately equals 30%. Thus, the glass substrate with the hemisphere pit arrays （HP glass） can effectively reduce the total reflectivity of a solar celt from 20% to 13%. The lip glass can also prolong the optical path length. The numerical results show that the total optical path length of the thin film Si solar cell covered with the HP glass increases from 2ω to 409. These results are basically consistent with the experimental results.

Beyond Lambertian light trapping for large-area silicon solar cells:fabrication methods

Light trapping photonic crystal(PhC)patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%,for light-to-electrical power conversion with a single junction cell.This is beyond the efficiency limit implied by the Lambertian limit of ray trapping~29%.The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap.We compare two different methods for surface patterning,that can be extended to large area surface patterning:1)laser direct write and 2)step-&-repeat 5×reduction projection lithography.Large area throughput limitations of these methods are compared with the established elec-tron beam lithography(EBL)route,which is conventionally utilised but much slower than the presented methods.Spec-tral characterisation of the PhC light trapping is compared for samples fabricated by different methods.Reflectance of Si etched via laser patterned mask was~7%at visible wavelengths and was comparable with Si patterned via EBL made mask.The later pattern showed a stronger absorbance than the Lambertian limit6.

Improving light trapping and conversion efficiency of amorphous silicon solar cell by modified and randomly distributed ZnO nanorods

Three-dimensional （3D） nanostructures in thin film solar cells have attracted significant attention due to their appli- cations in enhancing light trapping. Enhanced light trapping can result in more effective absorption in solar cells, thus leading to higher short-circuit current density and conversion efficiency. We develop randomly distributed and modified ZnO nanorods, which are designed and fabricated by the following processes： the deposition of a ZnO seed layer on sub- strate with sputtering, the wet chemical etching of the seed layer to form isolated islands for nanorod growth, the chemical bath deposition of the ZnO nanorods, and the sputtering deposition of a thin Al-doped ZnO （ZnO：Al） layer to improve the ZnO/Si interface. Solar cells employing the modified ZnO nanorod substrate show a considerable increase in solar energy conversion efficiency.

Light trapping enhanced broadband photodetection and imaging based on MoSe_(2)/pyramid Si vdW heterojunction

Two-dimensional(2D)layered materials have been considered promising candidates for next-generation optoelectronics.However,the performance of 2D photodetectors still has much room for improvement due to weak light absorption of planar 2D materials and lack of high-quality heterojunction preparation technology.Notably,2D materials integrating with mature bulk semiconductors are a promising pathway to overcome this limitation and promote the practical application on optoelectronics.In this work,we present the patterned assembly of MoSe_(2)/pyramid Si mixed-dimensional van der Waals(vdW)heterojunction arrays for broadband photodetection and imaging.Benefited from the light trapping effect induced enhanced optical absorption and high-quality vdW heterojunction,the photodetector demonstrates a wide spectral response range from 265 to 1550 nm,large responsivity up to 0.67 A·W^(-1),high specific detectivity of 1.84×10^(13)Jones,and ultrafast response time of 0.34/5.6μs at 0 V.Moreover,the photodetector array exhibits outstanding broadband image sensing capability.This study offers a novel development route for high-performance and broadband photodetector array by MoSe_(2)/pyramid Si mixed-dimensional heterojunction.

Metallic nanostructures for light trapping in energy-harvesting devices

Solar energy is abundant and environmentally friendly.Light trapping in solar-energy-harvesting devices or structures is of critical importance.This article reviews light trapping with metallic nanostructures for thin film solar cells and selective solar absorbers.The metallic nanostructures can either be used in reducing material thickness and device cost or in improving light absorbance and thereby improving conversion efficiency.The metallic nanostructures can contribute to light trapping by scattering and increasing the path length of light,by generating strong electromagnetic field in the active layer,or by multiple reflections/absorptions.We have also discussed the adverse effect of metallic nanostructures and how to solve these problems and take full advantage of the light-trapping effect.

Exceeding the limit of plasmonic light trapping in textured screen-printed solar cells using Al nanoparticles and wrinkle-like graphene sheets

The solar cell market is predominantly based on textured screen-printed solar cells.Due to parasitic absorption in nanostructures,using plasmonic processes to obtain an enhancement that exceeds 2.5%of the short-circuit photocurrent density is challenging.In this paper,a 7.2%enhancement in the photocurrent density can be achieved through the integration of plasmonic Al nanoparticles and wrinkle-like graphene sheets.For the first time,we experimentally achieve Al nanoparticle-enhanced solar cells.An innovative thermal evaporation method is proposed to fabricate low-coverage Al nanoparticle arrays on solar cells.Due to the ultraviolet(UV)plasmon resonance of Al nanoparticles,the performance enhancement of the solar cells is significantly greater than that from Ag nanoparticles.Subsequently,we deposit wrinkle-like graphene sheets over the Al nanoparticle-enhanced solar cells.Compared with planar graphene sheets,the bend carbon layer also exhibits a broadband light-trapping effect.Our results exceed the limit of plasmonic light trapping in textured screen-printed silicon solar cells.

Light Trapping Effect in Wing Scales of Butterfly Papilio peranthus and Its Simulations

Broadband light trapping effect and arrays of sub-wavelength textured structures based on the butterfly wing scales are applicable to solar cells and stealth technologies. In this paper, the fine optical structures in wing scales of butterfly Papilio peranthus, exhibiting efficient light trapping effect, were carefully examined. First, the reflectivity was measured by reflectance spectrum. Field Emission Scanning Electronic Microscope （FESEM） and Transmission Electron Microscope （TEM） were used to observe the coupling morphologies and structures of the scales. Then, the optimized 3D model of the coupling structure was created combining Scanning Electron Microscope （SEM） and TEM data. Afterwards, the mechanism of the light trapping effect of these structures was analyzed by simulation and theoretical calculations. A multilayer nano-structure of chitin and air was found. These structures are effective in increasing optical path, resulting in that most of the incident light can be trapped and adsorbed within the structure at last. Furthermore, the simulated optical results are consistent with the experimental and calculated ones. This result reliably confirms that these structures induce an efficient light trapping effect. This work can be used as a reference for in-depth study on the fabrication of highly efficient bionic optical devices, such as solar cells, photo detectors, high-contrast, antiglare, and so forth.

Strongly enhanced light trapping in a two-dimensional silicon nanowire random fractal array

We report on the unconventional optical properties exhibited by a two-dimensional array of thin Si nanowires arranged in a random fractal geometry and fabricated using an inexpensive,fast and maskless process compatible with Si technology.The structure allows for a high light-trapping efficiency across the entire visible range,attaining total reflectance values as low as 0.1%when the wavelength in the medium matches the length scale of maximum heterogeneity in the system.We show that the random fractal structure of our nanowire array is responsible for a strong in-plane multiple scattering,which is related to the material refractive index fluctuations and leads to a greatly enhanced Raman scattering and a bright photoluminescence.These strong emissions are correlated on all length scales according to the refractive index fluctuations.The relevance and the perspectives of the reported results are discussed as promising for Si-based photovoltaic and photonic applications.

Plasmonic light trapping for enhanced light absorption in film-coupled ultrathin metamaterial thermophotovoltaic cells

Ultrathin cells have gained increasing attention due to their potential for reduced weight, reduced cost and increased flexibility. However, the light absorption in ultrathin cells is usually very weak compared to the corresponding bulk cells. To achieve enhanced photon absorption in ultrathin thermophotovoltaic （TPV） cells, this work proposed a film-coupled metamaterial structure made of nanometer-thick gallium antimonide （GaSh） layer sandwiched by a top one-dimensional （1D） metallic grating and a bottom metal film. The spectral normal absorptance of the proposed structure was calculated using the rigorous coupled-wave algorithm （RCWA） and the absorption enhancement was elucidated to be attributed to the excitations of magnetic polariton （MP）, surface plasmon polariton （SPP）, and Fabry-Perot （FP） resonance. The mechanisms of MP, SPP, and FP were further confirmed by an inductor-capacitor circuit model, disper- sion relation, and phase shift, respectively. Effects of grating period, width, spacer thickness, as well as incidence angle were discussed. Moreover, short-circuit current density, open-circuit voltage, output electric power,and conversion efficiency were evaluated for the ultrathin GaSb TPV cell with a film-coupled metamaterial structure. This work will facilitate the development of next- generation low-cost ultrathin infrared TPV cells.

Highly efficient organic solar cells enabled by a porous ZnO/PEIE electron transport layer with enhanced light trapping

In this study,a porous inorganic/organic(ZnO/PEIE,where PEIE is polyethylenimine ethoxylated)(P-ZnO)hybrid material has been developed and adopted in the inverted organic solar cells(OSCs).The P-ZnO serving as the electron transport layer(ETL)not only presents an ameliorative work function,but also forms the cratered surface with increased ohmic contact area,revealing suppressed charge recombination and enhanced charge extraction in devices.Particularly,P-ZnO-based OSCs show improved light trapping in the active layer compared with ZnO-based ones.The universality of P-ZnO serving as ETL for efficient OSCs is verified on three photovoltaic systems of PBDB-T/DTPPSe-2 F,PM6/Y6,and PTB7-Th/PC_(71)BM.The enhancements of 8%in power conversion efficiency(PCE)can be achieved in the state-of-the-art OSCs based on PBDB-T/DTPPSe-2F,PM6/Y6,and PTB7-Th/PC_(71)BM,delivering PCEs of 14.78%,16.57%,and 9.85%,respectively.Furthermore,a promising PCE of14.13%under air-processed condition can be achieved for PZnO/PBDB-T/DTPPSe-2F-based OSC,which is among the highest efficiencies reported for air-processed OSCs in the literature.And the P-ZnO/PBDB-T/DTPPSe-2F-based device also presents superior long-term storage stability whether in nitrogen or ambient air-condition without encapsulation,which can maintain over 85%of its initial efficiency.Our results demonstrate the great potential of the porous hybrid PZnO as ETL for constructing high-performance and air-stable OSCs.

Ag nanoparticles preparation and their light trapping performance

Ag nanoparticles were fabricated on Si substrates by radio-frequency magnetron sputtering and thermal annealing treatments.It was found that Ag nanoparticles are ellipsoid at low annealing temperature,but the axis ratio decreases with the increase of annealing temperature,and a shape transformation from ellipsoid to sphere occurs when the temperature increases to a critical point.The experimental results showed that the surface plasmon resonances depend greatly on the nanoparticles'shape and size,which is in accordance with the theoretical calculation based on discrete dipole approximation.The results of forward-scattering efficiency(FSE) and light trapping spectrum(LTS) showed that Ag nanoparticles annealed at 400°C could strongly enhance the light harvest than those annealed at 300 and 500°C,and that the LTS peak intensity of the former is 1.7 and 1.5 times stronger than those of the later two samples,respectively.The conclusions obtained in this paper showed that Ag ellipsoid nanoparticles with appropriate size is more favorable for enhancing the light trapping.

Enhanced light trapping in periodically truncated cone silicon nanowire structure

Light trapping plays an important role in improving the conversion efficiency of thin-film solar cells. The good wideband light trapping is achieved using our periodically truncated cone Si nanowire （NW） structures, and their inherent mechanism is analyzed and simulated by FDTD solution software. Ordered cylinder Si NW structure with initial size orS0 nm and length of 200 nm is grown by pattern transfer and selective epitaxial growth. Truncated cone Si NW array is then obtained by thermal oxidation treatment. Its mean reflection in the range of 300-900 nm is lowered to be 5% using 140 nm long truncated cone Si NW structure, compared with that of 20% using cylinder counterparts. It indicates that periodically truncated Si cone structures trap the light efficiently to enhance the light harvesting in a wide spectral range and have the potential application in highly efficient NW solar cells.

Improving UV stability of perovskite solar cells without sacrificing efficiency through light trapping regulated spectral modification

The stability of perovskite solar cells is an important issue to be addressed for future applications.Perovskite solar cells are vulnerable to exposure to UV light due to promoted chemical reactions.However, preventing UV light from entering solar cells lowers the power conversion efficiency by reducing the photocurrent. The challenge is to improve UV stability without sacrificing efficiency. Here, we demonstrate the reduction of UV light-related negative effects from the perspective of spectral modification. By simultaneously introducing UV–visible downshifting and light trapping, perovskite solar cells can achieve a comparable efficiency of over 21% to that of an unmodified device. The optimized device obtains increased UV stability due to UV–visible downshifting. Different from other strategies, spectral modification externally alters the composition of incident light and improves UV stability without changing the internal device architecture, which is broadly applicable to perovskite solar cells with different structures. The present work may also find applications in other types of solar cells to boost the stability of devices exposed to UV light.

Intermittent chaos for ergodic light trapping in a photonic fiber plate

Extracting the light trapped in a waveguide,or the opposite effect of trapping light in a thin region and guiding it perpendicular to its incident propagation direction,is essential for optimal energetic performance in illumination,display or light harvesting devices.Here we demonstrate that the paradoxical goal of letting as much light in or out while maintaining the wave effectively trapped can be achieved with a periodic array of interpenetrated fibers forming a photonic fiber plate.Photons entering perpendicular to that plate may be trapped in an intermittent chaotic trajectory,leading to an optically ergodic system.We fabricated such a photonic fiber plate and showed that for a solar cell incorporated on one of the plate surfaces,light absorption is greatly enhanced.Confirming this,we found the unexpected result that a more chaotic photon trajectory reduces the production of photon scattering entropy.

Plasmonic light trapping for wavelength-scale silicon solar absorbers

Light trapping is of critical importance for constructing high efficiency solar cells. In this paper, we first reviewed the progress we made on the plasmonic light trapping on Si wafer solar cells, including AI nanoparticle （NP）/SiNx hybrid plasmonic antireflection and the Ag NP light trapping for the long-wavelength light in ultrathin Si wafer solar cells. Then we numerically explored the maximum light absorption enhancement by a square array of Ag NPs located at the rear side of ultrathin solar cells with wavelength-scale Si thickness. Huge absorption enhancement is achieved at particular long wavelengths due to the excitation of the plasmon-coupled guided resonances. The photocurrent generated in 100 nm thick Si layers is 6.8 mA/cm2, representing an enhancement up to 92% when compared with that （3.55 mA/cm2） of the solar cells without the Ag NPs. This study provides the insights of plasmonic light trapping for ultrathin solar cells with wavelength-scale Si thickness.

Development of an automatic monitoring system for rice light-trap pests based on machine vision

Monitring pest populations in paddy fields is important to effectively implement integrated pest management.Light traps are widely used to monitor field pests all over the world.Most conventional light traps still involve manual identification of target pests from lots of trapped insects,which is time-consuming,labor-intensive and error-prone,especially in pest peak periods.In this paper,we developed an automatic monitoring system for rice light-trap pests based on machine vision.This system is composed of an itelligent light trap,a computer or mobile phone client platform and a cloud server.The light trap firstly traps,kills and disperses insects,then collects images of trapped insects and sends each image to the cloud server.Five target pests in images are automatically identifed and counted by pest identification models loaded in the server.To avoid light-trap insects piling up,a vibration plate and a moving rotation conveyor belt are adopted to disperse these trapped insects.There was a close correlation(r=0.92)between our automatic and manual identification methods based on the daily pest number of one-year images from one light trap.Field experiments demonstrated the effectiveness and accuracy of our automatic light trap monitoring system.

Comparative Human Landing Catch and CDC Light Trap in Mosquito Sampling in Knowlesi Malaria Endemic Areas in Peninsula Malaysia

Adult mosquito sampling techniques are essential for monitoring transmission of malaria and other mosquito borne infections. Preference for any sampling technique depends on both its field efficiency and the characteristics of local vector populations. Surveys on adult mosquitoes using Human Landing Catch (HLC) and CO2-baited CDC light trap (CDC-LT) techniques were conducted in several knowlesi malaria endemic areas between the months of March to December 2012 in several states of Peninsula Malaysia. These two techniques were relatively compared to determine the preferences of anopheline mosquitoes towards CO2-baited CDC-LT technique using HLC technique as the reference method. Cx. gelidus, An. maculates and An. introlatus were the main three species collected by HLC technique, whereas the species collected by CO2-baited CDC-LT technique were mostly An. cracens, Ar. durhami and Coquillettidia species. Most of the Anopheles species were collected almost exclusively by the human collectors except for An. cracens and An. introlatus which were collected using both techniques. Anopheles cracens was the most dominant species captured using CO2-baited CDC-LT technique. This is the first report showing An. cracens was caught using CO2-baited CDC-LT technique in Malaysia.

The Role of Mineral and Natural Oils in Integration with Inorganic Salts and Some Insecticides in Suppressing the Invasion of the Red Palm Weevil Rhynchophorus ferrugineus (RPW) Affecting Date Palms with Estimation of Its Residues in the Resulting Date Fruits

Applied experiments were conducted in the palm orchard in the Nubaria region. The orchard includes the varieties of Al-Barhi (imported) and Zaghloul (local) to examine the efficacy of some natural materials alone and in combination with some pesticides against the Red Palm Weevil Rhynchophorus ferrugineus (RPW) that infects palm trees in Egypt. Most insects caught by light traps, which have a role in the spread of the red palm weevil in palm groves, appear in early February and March. Peak numbers for the month of May until September namely Phyllgnathus excavatus. Pseudophilus testaceus, Phonapata frontalis, and Oryctes elegans. The neglected gardens of date palms are more compensating for insect infestation than those maintained in terms of agricultural and pest control services. Individual injection of insecticide (Mosspilan) was the most potent against RPW-infested Barhi var. with a recovery rate of 91.7%, followed by Selikron at 80%, and finally Saydon at 37.5%. Injection of the car oil used with Mosspilan followed by Selikron was effective against RPW. No significant difference between treatments of injection (F-value: 1.2). Mixing injection of mineral oils with chemical pesticides is effective against red palm weevil after two successive seasons. As a result, the pesticide was poured around the affected palm root, with a low recovery rate. There is no effect of palm spray. The best way to control the red palm weevil is the method of injecting the tested material (single or mixed) with the pure pesticide into the trunk of the infected palm tree. The tested pesticide residues gradually decrease as the period after application is prolonged with an average loss of 0.12, 0.02 and 0.07 ppm after 90 consecutive days. .

Absorption enhancement in thin film a-Si solar cells with double-sided SiO_2 particle layers

Light absorption enhancement is very important for improving the power conversion efficiency of a thin film a-Si solar cell. In this paper, a thin-film a-Si solar cell model with double-sided SiO2 particle layers is designed, and then the underlying mechanism of absorption enhancement is investigated by finite difference time domain（FDTD） simulation;finally the feasible experimental scheme for preparing the SiO2 particle layer is discussed. It is found that the top and bottom SiO2 particle layers play an important role in anti-reflection and light trapping, respectively. The light absorption of the cell with double-sided SiO2 layers greatly increases in a wavelength range of 300 nm-800 nm, and the ultimate efficiency increases more than 22% compared with that of the flat device. The cell model with double-sided SiO2 particle layers reported here can be used in varieties of thin film solar cells to further improve their performances.

Optical management in organic photovoltaic devices

Due to their potentials in light‐weight,flexible,and semitransparent devices,organic photovoltaics are of great significance in the field of renewable energy.However,the narrow intrinsic absorption spectrum of organic materials hinders the full utilization of solar energy.To fabricate a highly efficient opaque solar cell,it is greatly necessary to modify the optical properties of the device to improve light absorption.In addition,the growing interest in building‐integrated photovoltaics drives the development of semitransparent devices.The preparation of semitransparent solar cells with excellent performance imposes high requirements on the high efficiency and appropriate visible light transmittance of effective optical management.In this review,the recent research progress of optical management in organic photovoltaics is reviewed,including the design of light‐absorbing materials,the modification of different layers,adding a lighttrapping structure,and changing the light absorption capabilities of specific materials,so as to provide strategies of how to improve the performance of organic photovoltaic devices and present the prospect of the area.