Reduce Reflection Losses Research Articles

Optical and Thermal Emission Benefits of Differently Textured Glass for Photovoltaic Modules

Textured glass is a possible means for reflection reduction of a photovoltaic module. Texturing not only increases the energy yield of the system through reduced reflection losses, but also can play a role in dissipating waste heat through enhancing convective and radiative heat loss. In this work, we describe three textured glass surfaces analytically and model them numerically at optical (400–1050 nm) and mid-infrared (MIR, 5–30 μm) wavelengths. Spectral and directional results are processed with a series of weight functions to evaluate the total transmission to determine the optical performance and the total MIR hemispherical emissivity for the thermal performance. It is found that the proposed textured surfaces could improve the total optical transmission by 3.3%–4.6% relative to planar glass for direct solar radiance and 4.9%–6.7% for diffuse component, whereas the total MIR hemispherical emissivity is boosted by 6.6%–9.3% relative. The current most commercially favored inverted pyramid pattern may not be the most effective glass surface texturing scheme based on optical and radiative enhancement or self-cleaning properties.

Bilayer broadband antireflective coating to achieve planar heterojunction perovskite solar cells with 23.9% efficiency

Although perovskite solar cells (PSCs) have achieved encouraging efficiency, the photon loss at the substrate due to light reflection has not been well addressed. Light management is promising to reduce reflection loss and realize higher power conversion efficiency (PCE) of PSCs. Here, a bilayer antireflective coating (ARC) has been designed and coated onto the backside of the glass substrate of (FAPbI3) x -(MAPbBr3)1− x PSCs to enhance photon harvesting and consequently the device efficiency. The bottom layer of the bilayer ARC is made from a silica polymer and the top layer is made from the mixture of hexamethyldisiloxane-modified mesoporous silica nanoparticles and a fluorinated silica polymer. By adjusting the refractive index and the film thickness of each layer according to a two-layer model, enhanced glass transmittance in a broadband wavelength range can be reached, with the maximum transmittance increasing from ca. 90% to over 95%. With the bilayer ARC, the maximum short-circuit current density and PCE of (FAPbI3) x (MAPbBr3)1− x PSCs can be increased from 25.5 mA cm−2 and 22.7% to 26.5 mA cm−2 and 23.9% with negligible changes in fill factor and open-circuit voltage. This work presents a simple yet effective strategy to enhance the efficiency of solar cells employing bilayer antirefective coatings, which can be applied to other types of solar cells.

Light Reflection Loss Reduction by Nano-Structured Gratings for Highly Efficient Next-Generation GaAs Solar Cells

This paper mainly focuses on increasing the conversion efficiency of GaAs solar cells by reducing the light reflection losses. The design of nano-structured gratings and their light trapping performance are modelled and optimised by using the finite-difference time-domain (FDTD) method. The sunlight directly impinges on the solar panel or cells, then a portion of the incident sunlight reflects back to the air from the surface of the panel, thus leading to a reduction in the light absorption capacity of the solar cells. In order to proliferate the light absorption capacity of solar cells nano-grating structures are employed, as they are highly capable of capturing the incident sunlight compared to a conventional (or flat type) solar cell, which results in generating more electrical energy. In this study, we design three different types of nano-grating structures, optimise their parameters and their performance in light capturing capacity. From the simulation results, we confirm that that it is possible to reduce light reflection losses up to 27%, by using the nano-grating structures, compared to conventional type solar cells. This reduction of reflection losses helps to improve the conversion efficiency of next-generation GaAs solar cells significantly for a sustainable green Earth.

Improved Quantum Efficiency by Advanced Light Management in Nanotextured Solution-Processed Perovskite Solar Cells

Light management strategies can increase the efficiency of perovskite single-junction and tandem solar cells. In this study, we present perovskite solar cells deposited on different shallow nanotextures by spin-coating. A morphological and optoelectronic analysis demonstrates a high quality of the perovskite absorber, regardless of the substrate. Using both, a nanotexture and a sodium fluoride antireflective coating, enables us to improve the power conversion efficiency by 1.0%abs to 19.7%, when compared to its planar reference. A characterization of the optical performance of nanotextured perovskite solar cells and rigorous optical simulations reveal that the gain in efficiency can be largely attributed to reduced reflection losses and therefore increased absorption in the perovskite. Our nanotextured perovskite solar cells reach 93.6% of the attainable current density, marking the highest reported value for perovskite single-junctions and approaching those of established photovoltaic technologies. Our results demonstrate that nanotextures can be applied to solution-processed perovskite solar cells and pave the way to increased power conversion efficiencies by light management not only in perovskite single-junction but also perovskite–silicon tandem solar cells.

Carbon-rich amorphous silicon carbide and silicon carbonitride films for silicon-based photoelectric devices and optical elements: Application from UV to mid-IR spectral range

Abstract In the work we demonstrated the possibility to apply amorphous non-stoichiometric silicon carbide (a-SixC1-x:H) and silicon carbonitride (a-SixC1-x-yNy:H) films for improvement of exploitation characteristics of silicon-based photoelectric devices and optical elements in very wide spectral range - from UV to mid-IR. The a-SixC1-x:H films possessing optical properties required for effective antireflection (AR) effects for silicon (refractive index (n) at λ = 632 nm from 1.86 to 1.98, optical bandgap (Eopt) from 2.7 to 3.1 eV, and extinction coefficient (k) is close to zero practically in all spectral range) were obtained by PE-CVD from methane, silane, hydrogen, and argon gas mixture. To deposit silicon carbonitride films some amount of nitrogen was added to the gas mixture. For the a-SixC1-x-yNy:H films the following optical parameters were obtained: n = 1.76–1.93, Eopt = 3.1–3.4 eV, k~0. It has been shown that the proposed films possess unique mechanical properties and ratio of the films hardness to their Young modulus is very high (H/E > 0.13). It is evidence of the films high wear resistance that is of great importance when the films are used for protection of silicon optical elements in IR spectral range. It is established that the films of both types are very suitable as excellent AR coatings for silicon in the spectral range of Si-based solar cell photosensitivity, telecommunication windows, and mid-IR. Deposition of even single layer AR film allowed us to reduce reflection losses significantly (reflection coefficient (R) at minimum of reflection becomes close to zero). As a result, efficiency of etched multicrystalline Si-based solar cell (SC) was significantly improved. Transmittance of Si-based optical elements with front and rear AR films reached practically 100% in the telecommunication windows spectral range.

Sb2Se3 thin film solar cells prepared by pulsed laser deposition

Abstract Sb2Se3, a very promising absorber layer for thin film solar cells, has attracted more and more attention because of its special structural and optical properties. In this work, pulsed laser deposition (PLD), a simple and effective technique, was used to deposit CdS/Sb2Se3 solar cells for the first time. Results show that the grain size is 200–250 nm, the bandgap is calculated to be 1.21 eV and Sb2Se3 thin film with thickness of 400 nm is more suitable for solar cells. To reduce reflection loss, lattice mismatch and shunt pathways, SnO2 high resistive layer was introduced into Sb2Se3 solar cells. Due to the introduction of SnO2, overall performance, especially Jsc, was improved and champion device was achieved with efficiency of 4.77%.

Progress and Perspective of Near-Ultraviolet and Deep-Ultraviolet Light-Emitting Diode Packaging Technologies

Abstract Ultraviolet light-emitting diodes (UV-LEDs) have drawn considerable attention in environment, life science, and industry fields, such as the applications of near UV-LEDs in resin curing, illumination, and identification, and deep UV-LEDs in disinfection, medical treatment, and biochemical inspection. However, due to the limitation of packaging technology, UV-LED devices exhibit low light efficiency and poor reliability compared with visible LEDs. The organic encapsulation materials are prone to UV aging, thermal degradation, and nonairtightness, which significantly reduce the performances of UV-LEDs. In order to solve this issue, UV-LED packaging technology has been proposed for UV-LED devices instead of conventional LED packaging. In this review, we investigated in detail the overview and challenges of near-ultraviolet light-emitting diodes (NUV-LED)/deep-ultraviolet light-emitting diodes (DUV-LED) packaging. For the packaging of UV-LEDs, all inorganic encapsulation materials, hermetic packaging structures with low-temperature bonding, reduced reflection losses, UV stable and transparent materials, and effective thermal management are key progresses to enhance the light efficiency and reliability of UV-LEDs. In addition, the summary and perspectives of NUV-LED/DUV-LED packaging were introduced and discussed.

Design and Fabrication of a Multifunctional Flexible Absorber (Flexorb) in the UV–Vis–NIR Wavelength Range

AbstractSynthesis of a near perfect absorber is required for many technologically challenging areas. Most of the existing super absorbers are rigid and usually exploit the light in the visible range only leaving a significant part of available energy in the solar spectrum unutilized. Here the synthesis of a multifunctional flexible absorber (flexorb) with an ultrahigh absorbing capacity of >99% in the whole UV–vis–NIR region is reported. Flexorb is fabricated by texturing the polydimethylsiloxane matrix reinforced by ZnO nanorods, Fe particles and carbon nanotubes (CNTs). The near perfect absorbing behavior of flexorb emanates from two factors: 1) the multiple scattering and subsequent trapping of incident light induced by texturing and fillers having varying geometries and aspect ratios and 2) reduced reflection losses at the flexorb/surrounding interface due to impedance matching provided by CNTs. The flexibility of flexorb ensures that it can be deformed in a variety of shapes without any damage or creasing failure and can be readily mounted on surfaces made of stainless steel, glass, or acrylic polymer. It is believed that the present work will trigger further research to develop flexible multifunctional absorbers for harnessing the solar energy in the broader spectrum for various applications.

Enhance the solar cell efficiency by reduction of reflection losses

The enhancement of the solar cell efficiency field has been achieved in many methods due to the different factors and conditions that led to loss the solar energy. This work deals with the increasing of the efficiency of solar cell that made of single crystalline silicon. This increment achieved by the reduction of biggest type of losses of the conversion efficiency named reflection. by using two methods first; forming grooves on the surface using pulse Nd:YAG laser with max energy 1J and pulse width 10ns, using the fast and accurate movement of the 3D optical galvo mirror scanning system to form the grooves, the second method was by deposition nanomaterials as Silver (Ag) and Cadmium telluride (CdTe) to constitute an antireflection layer for the incident solar spectrum. The effect of antireflection layer material type and the effect of incident light angle on the reflection had been studied in this work. The reflectance had been measured by a system designed and built to give the reflection for angles ranged 0 – 180 degree controlled by Microcontroller. The result inducate that increase in conversion efficiency was 28.3% for Ag/Si, and 32.9% for CdTe/Si than the original efficiency of Si solar cell.

Thin-Film SUEX as an Antireflection Coating for mmW and THz Applications

We present a simple process for depositing SUEX dry films to realize effective antireflection coatings on high-resistivity silicon wafers and lenses. Heat-assisted conformal deposition of SUEX film followed by curing via ultraviolet exposure achieves robust adhesion to the silicon lens surface. Due to its relatively low material loss and commensurate refractive index, quarter-wavelength-thick SUEX coatings minimize reflection losses and significantly improve signal coupling into high-index silicon lenses. As an example, a 150- $\mu$ m-thick SUEX layer was conformally coated on a 1-cm-diameter high-resistivity silicon lens to reduce reflection loss to less than 4% over the 220–325 GHz band.

Influence of pyramid size on reflectivity of silicon surfaces textured using an alkaline etchant

Surface texturing of p-type monocrystalline silicon (100) is well known as one of the best methods to reduce reflection losses and to increase light trapping and light absorption probability. Pyramid surface textures play a major role in reducing the reflectance of monocrystalline silicon surfaces. In this paper, the size of pyramids formed on the surface of p-type silicon substrates and by changing the etching characteristics during the texturing process of silicon were studied and evaluated. The pyramids that formed on the crystalline silicon surface formed light traps that led to increased light absorption efficiency. The pyramid size effects on the percent reflectivity were evaluated at normal incidence and an inverse relationship between the percent reflectivity and the pyramid size was found. The size of the pyramids was controlled by controlling the texturing process by changing the concentrations of potassium hydroxide (KOH) and isopropyl alcohol (IPA) and by controlling the etching process time. In this work, the optimized etching conditions were determined as a solution prepared with 20 wt% KOH and 3 wt% IPA for wet etching at a reaction temperature of \(80^{\circ }\hbox {C}\) and an etching time of 40 min. The lowest value for percent reflectivity of the patterned surfaces was 9.7% and it was achieved for pyramid bases close to \(4~\upmu \hbox {m}\) as measured at a wavelength of 650 nm.

Model for Characterization and Optimization of Spectrally Selective Structures to Reduce the Operating Temperature and Improve the Energy Yield of Photovoltaic Modules

Many existing commercially manufactured photovoltaic modules include a cover layer of glass, commonly coated with a single layer antireflection coating (ARC) to reduce reflection losses. As many common photovoltaic cells, including c-Si, CdTe, and CIGS, decrease in efficiency with increasing temperature, a more effective coating would increase reflection of sub-bandgap light while still acting as an antireflection coating for higher energy photons. The sub-bandgap reflection would reduce parasitic sub-bandgap absorption and therefore reduce operating temperature. This reduction under realistic outdoor conditions would lead to an increase in annual energy yield of a photovoltaic module beyond what is achieved by a single layer ARC. However, calculating the actual increase in energy yield provided by this approach is difficult without using time-consuming simulation. Here, we present a time-independent matrix model which can quickly determine the percentage change in annual energy yield of a module with a s...

Performance enhancement of a photovoltaic panel with reflectors and cooling coupled to a solar still with air injection

The present study aims to overcome the problems of freshwater and electricity in remote areas. To achieve this, a hybrid system of photovoltaic (PV) panel with reflectors and cooling coupled developed solar still with air injection was experimentally investigated. This study aims to improve the PV panel performance using reflectors with cooling. The cooling was used to reduce the PV surface temperature. On the other hand, reflectors are used to reduce reflection loss and increase the rate of solar radiation absorbed by PV panels. To obtain the best cooling technique of the PV panel with reflectors, the five operating cases was studied, namely case-A (conventional PV panel), case-B (PV with reflectors), case-C (PV with reflectors and air cooling technique), case-D (PV with reflectors and water cooling technique), and case-E (PV with reflectors, water and air cooling techniques). The cooling air out from the PV module for the two cases C and E were injected inside the developed solar still to increase the evaporation rate within the solar still, thereby improving the freshwater productivity. The results show that the improvement in the electrical power of the PV panel was recorded 16.81, 21.62, 35.13, and 39.69% for cases B, C, D, and E, respectively compared to case-A. Also, using the air injection system improved the freshwater production by 40.98% and 21.96% for cases C and E, respectively compared to the case without air injection system. The average overall efficiency of the hybrid system was recorded 21.2, 22.1, 30.55, 22.95, and 27.15% for cases A, B, C, D, and E, respectively. Moreover, the economic analysis presented that the estimated cost of kWh and fresh water production vary between 0.076 and 0.083 $/kWh and 0.01–0.014 $/L, respectively.

Minimization of Reflection-Loss from Etched Nano-structures of Silicon Crystal Wafers

Abstract Significant reduction in reflection loss from crystalline silicon absorber layer is an urgent requirement for increasing the efficiency of solar cells. Present research targets on producing almost black-Si by H2-plasma etching of the c-Si wafers, using planar inductively-coupled plasma-CVD. It is demonstrated that lower gas pressure in the plasma promotes efficient etching of c-Si surface. Plasma etching at 30 mTorr and 200 °C produces, high-density, homogeneous and uniform pyramid-like Si-nanostructures with dimension ∼40–200 nm which closely satisfies the anti-reflection coating (ARC) requirement. An extremely low reflection (∼0.13%) from such optimally etched silicon nanostructures appears most useful for photovoltaic applications

The performance and durability of single-layer sol-gel anti-reflection coatings applied to solar module cover glass

Abstract A significant source of energy loss in photovoltaic (PV) modules is caused by reflection from the front cover glass surface. Reflection from the cover glass causes a loss of ~4% at the air-glass interface. Only a single air-glass interface can be coated on crystalline silicon solar modules as an ethylene-vinyl acetate (EVA) layer is inserted between the cover glass and the silicon absorber. A single-layer anti-reflection coating (ARC) on the outer surface of the cover glass is effective at reducing reflection losses over the wavelength range of most PV devices. The coating investigated in this work reduces the reflectance loss at the glass surface by 74%. However, the long-term durability of sol-gel coatings has not been established particularly for use in hot and humid climates. In this work, we investigate the damage resistance of a single-layer closed-surface hard coat ARC, deposited using sol-gel methods by applying a variety of accelerated weathering, scratch and abrasion test methods. The reflectance of the sol-gel ARC was measured and then the coating was put through a series of durability and environmental tests. The coating is resistant to damage from heating and can withstand temperatures higher than the phase change temperature of soda-lime glass. Scratch testing demonstrated that the sol-gel AR is relatively hard and difficult to remove from the substrate surface. Pull tests and cross-hatch testing also confirmed the strong adhesion of the coating. Weathering experiments show some degradation in weighted average reflectance, particularly an increase in reflectance of 0.6–0.9% after 1000 h of exposure to damp heat. Testing also showed a vulnerability to exposure to acid. These results indicate that the performance of this type of ARC could deteriorate and possibly delaminate in humid climate conditions The ARC had a low water contact angle, which means the coatings are hydrophilic and, therefore, hygroscopic increasing the risk of water damage over extended periods of time. This work shows that sol-gel anti-reflection coatings are currently unsuitable for use on PV and are unlikely to remain durable across the 25 year industry standard.

Improvement in CIGS solar cell efficiency using a micro-prism array integrated with sub-wavelength structures

Abstract A micro-prism array (MPA) integrated with subwavelength structures (SWSs) was employed to improve the efficiency of a CuIn1-xGaxSe2 (CIGS) solar cell by minimizing optical reflection losses caused by the metal grids. The MPA mounted on the CIGS solar cell refracted incident light normal to the grid into the nearby surface of the solar cell, thereby minimizing the optical reflection losses caused by the metal grids. Furthermore, to reduce reflection losses at the surface of the MPA, SWSs were formed on the MPA glass. This resulted in increased photovoltaic current, which enhanced the power conversion efficiency (PCE) of the solar cells. The final short circuit current density and the PCE of the CIGS solar cells with MPA glass integrated with SWSs were improved by 9.0% and 8.5%, respectively, compared with those of a CIGS solar cell without cover glass.

Pass-Band Characteristics of an L-Shaped Waveguide in a Diamond Structure Photonic Crystal

The conduction characteristics of a L-shaped waveguide in a diamond structure photonic crystal is investigated in this paper. The waveguides were fabricated with titanium dioxide ceramic via 3-D printing and sintering. The effects of the position and size of line defects on the transmission characteristics are first simulated using a finite-difference time-domain method. The simulated results show that, when the length of the rectangular defect equals the lattice constant, multiple extended modes are generated. When the centers of the single unit cell of the diamond structure and the line defect waveguide coincide, higher transmission efficiency in the line defect can be achieved. In addition, the corner of the L-shaped waveguide was optimized to reduce reflection loss at the turning point using the arc transition of the large diameter. Our experimental results indicate that L-shaped waveguides with an optimized photonic band gap structure and high-K materials can produce a pass-band between 13.8 GHz and 14.4 GHz and increase transmission efficiency. The computed results agree with the experimental results. Our results may help the integration of microwave devices in the future and possibly enable new applications of photonic crystals.

Enhanced Light Absorption in Concentrated GaInP/GaAs/Ge Solar Cells Using a Secondary Optical Element with Subwavelength Structures

A secondary optical element (SOE) with a subwavelength structure (SWS) was developed and incorporated on a GaInP/GaAs/Ge triple-junction solar cell. The nanoscale SWS was realized by dry etching using a silver (Ag) nanomask. The fabricated SWS SOE was mounted on a triple-junction solar cell. The SWS SOE exhibited improved transmittance in the broadband wavelength range from 350 to 1800 nm. Compared with SOE without SWS, the average transmittance was improved by 2.43%. The power-conversion efficiency (PCE) of the CPV module with the SWS SOE was 28.4%, whereas the PCE of the module without SWS was 27.8%. The enhanced efficiency of the CPV module is ascribed to improved current density due to reduced reflection losses at the surface of the SWS SOE.

A New Approach to Design Autonomous Wireless Sensor Node Based on RF Energy Harvesting System.

Energy Harvesting techniques are increasingly seen as the solution for freeing the wireless sensor nodes from their battery dependency. However, it remains evident that network performance features, such as network size, packet length, and duty cycle, are influenced by the sum of recovered energy. This paper proposes a new approach to defining the specifications of a stand-alone wireless node based on a Radio-frequency Energy Harvesting System (REHS). To achieve adequate performance regarding the range of the Wireless Sensor Network (WSN), techniques for minimizing the energy consumed by the sensor node are combined with methods for optimizing the performance of the REHS. For more rigor in the design of the autonomous node, a comprehensive energy model of the node in a wireless network is established. For an equitable distribution of network charges between the different nodes that compose it, the Low-Energy Adaptive Clustering Hierarchy (LEACH) protocol is used for this purpose. The model considers five energy-consumption sources, most of which are ignored in recently used models. By using the hardware parameters of commercial off-the-shelf components (Mica2 Motes and CC2520 of Texas Instruments), the energy requirement of a sensor node is quantified. A miniature REHS based on a judicious choice of rectifying diodes is then designed and developed to achieve optimal performance in the Industrial Scientific and Medical (ISM) band centralized at . Due to the mismatch between the REHS and the antenna, a band pass filter is designed to reduce reflection losses. A gradient method search is used to optimize the output characteristics of the adapted REHS. At of input RF power, the REHS provides an output DC power of and a comparison with the energy requirement of the node allows the Base Station (BS) to be located at from the wireless nodes when the Wireless Sensor Network (WSN) has nodes evenly spread over an area of and when each round lasts . The result shows that the range of the autonomous WSN increases when the controlled physical phenomenon varies very slowly. Having taken into account all the dissipation sources coexisting in a sensor node and using actual measurements of an REHS, this work provides the guidelines for the design of autonomous nodes based on REHS.

Nanostructured antireflective in-plane solar harvester.

In this work, we demonstrate a two-dimensional nano-hole array that can reduce reflection losses while passively trapping and harvesting incident light. The surface structure is designed to scavenge a small portion of incident light that would typically be lost due to Fresnel reflection, while the majority of light transmits unobstructed like a regular window. The trapping mechanism is dependent on angle and wavelength, and can be designed to selectively trap narrow wavelength bands using the constructed theoretical models. We demonstrate that structures with periods of 275 nm and 325 nm can trap different wavelength range within the visible spectrum, while simultaneously suppressing reflection losses. The trapping effect can be observed visually, and can be converted to a current output using a photovoltaic (PV) cell on the glass edge. The fabrication of such materials employs a simple replication process, and can be readily scaled up for large-scale manufacturing. The demonstrated solar harvester can be potentially be widely deployed in residential and commercial buildings as multifunctional windows for solar energy harvesting, scavenging, spectra splitting, and anti-glare properties.