Double Antireflection Coatings Research Articles

Ray Tracer Simulation of Si-Based Solar Cells using Al2O3/ITO as Double Layers Anti Reflective Coating

The solar cell has become one of the options for a greener world. Various studies have been done to achieve a solar cell with high efficiency and reasonable price. This study’s objective is to investigate how the thickness and base angle of the front layer affect the optical and electrical characteristics of Si-Based Solar cells. To accomplish this study, heterojunction solar cells using Al2O3/ITO as the double layer anti-reflection coating are analyzed using the Wafer Ray Tracer simulation by the PV Lighthouse. Al2O3 and ITO layers are used as a double anti-reflection coating (DLARC) in the light trapping strategy to support the reflection, absorption, and transmission (R, A and T) of the silicon solar cell. It acts to minimize reflectance and improves the overall efficiency of the solar cell. DLARC variation focuses on increasing absorption while decreasing reflection and transmission. The high refractive index of the hydrogenated a-Si (a-Si: H) emitter layer generates excessive reflection losses in SHJ solar cells making the silicon wafer have a low absorption efficiency. The DLARC thickness and base angle are varied as part of the simulation using the Wafer Ray Tracer by PV Lighthouse. The surface morphology of upright pyramid texture, height is 3.536 µm, texture base angle 54.74 °, and width 5 µm are used for reference scheme. Four schemes will be analyzed throughout this study along with the reference scheme. The result of this study is that Scheme 3 gives the optimum result with 99 % absorption, 21 % reflection and 67 % transmission. The goal of this study is to evaluate the impact of ARC thickness on optical and electrical characteristics. The best outcome is produced by varying the thickness and base angle of Scheme 3. The highest Jmax value, 0.3842 mA/cm2, is found in Scheme 3. HIGHLIGHTS The high refractive index of the hydrogenated a-Si (a-Si: H) emitter layer causes significant reflection losses in SHJ solar cells, resulting in a low absorption efficiency for the silicon wafer The double anti-reflection coating (DLARC) thickness and base angle are modified as part of the simulation using PV Lighthouse's Wafer Ray Tracer The best results are obtained by adjusting the thickness and base angle of Scheme 3. Scheme 3 has the highest Jmax value of 0.3842 mA/cm2 GRAPHICAL ABSTRACT

Recent Applications of Antireflection Coatings in Solar Cells

The antireflection coating (ARC) suppresses surface light loss and thus improves the power conversion efficiency (PCE) of solar cells, which is its essential function. This paper reviews the latest applications of antireflection optical thin films in different types of solar cells and summarizes the experimental data. Basic optical theories of designing antireflection coatings, commonly used antireflection materials, and their classic combinations are introduced. Since single and double antireflection coatings no longer meet the research needs in terms of antireflection effect and bandwidth, the current research mainly concentrates on multiple layer antireflection coatings, for example, adjusting the porosity or material components to achieve a better refractive index matching and the reflection effect. However, blindly stacking the antireflection films is unfeasible, and the stress superposition would allow the film layer to fail quickly. The gradient refractive index (GRIN) structure almost eliminates the interface, which significantly improves the adhesion and permeability efficiency. The high-low-high-low refractive index (HLHL) structure achieves considerable antireflection efficiency with fewer materials while selecting materials with opposite stress properties improves the ease of stress management. However, more sophisticated techniques are needed to prepare these two structures. Furthermore, using fewer materials to achieve a better antireflection effect and reduce the impact of stress on the coatings is a research hotspot worthy of attention.

Performance Improvement of npn Solar Cell Microstructure by TCAD Simulation: Role of Emitter Contact and ARC

In the current study, the performance of the npn solar cell (SC) microstructure is improved by inspecting some modifications to provide possible paths for fabrication techniques of the structure. The npn microstructure is simulated by applying a process simulator by starting with a heavily doped p-type substrate which could be based on low-cost Si wafers. After etching deep notches through the substrate and forming the emitter by n-type diffusion, an aluminum layer is deposited to form the emitter electrode with about 0.1 µm thickness; thereby, the notches are partially filled. This nearly-open-notches microstructure, using thin metal instead of filling the notch completely with Al, gives an efficiency of 15.3%, which is higher than the conventional structure by 0.8%. Moreover, as antireflection coating (ARC) techniques play a crucial role in decreasing the front surface reflectivity, we apply different ARC schemes to inspect their influence on the optical performance. The influence of utilizing single layer (ZnO), double (Si3N4/ZnO), and triple (SiO2/Si3N/ZnO) ARC systems is investigated, and the simulation results are compared. The improvement in the structure performance because of the inclusion of ARC is evaluated by the relative change in the efficiency (Δη). In the single, double, and triple ARC, Δη is found to be 12.5%, 15.4%, and 17%, respectively. All simulations are performed by using a full TCAD process and device simulators under AM1.5 illumination.

Design and Simulation of Triple Layer Antireflection Coating for Silicon Solar Cells

In present work an attempt has been made to investigate the effect of triple layer anti-reflection coating (TLARC) on the surface of silicon cell theoretically. In this regard, MgF2, Si3N4, and TiO2 have been used to design anti-reflection coatings (ARC). Reflection spectra for single double and triple layer ARCs have been evaluated numerically using transfer matrix method (TMM). Numerically calculated reflection spectra for single, double, and triple layer anti-reflection coatings further used in PC1D simulator to study the performance of silicon solar cell. Result shows reduction in reflectance of silicon solar cell down to less than 3% in the wavelength range 400 – 1200 nm with conversion efficiency 21.6% for TLARC (MgF2/Si3N4/TiO2).

Influence of minority charge carrier lifetime and concentration on crystalline silicon solar cells based on double antireflection coating: A simulation study

In this work, the optoelectrical properties of silver doped zinc oxide (Ag–ZnO)/ZnO double antireflection coating (ARC) layer were investigated by a simulation approach in terms of their minority charge carriers and surface charge carrier concentrations. From the experimental results, the Ag–ZnO/ZnO double ARC layer on Si solar cells presented the reduced average reflectance by 7.58% which was lowered to ZnO and Ag–ZnO single ARC layer. The simulation study demonstrated the reasonable electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 on c-Si solar cells with Ag–ZnO/ZnO double ARC layer. The simulated I–V characteristics evidenced that the performances of Ag–ZnO/ZnO double ARC layer-based Si solar cells gradually increased with the increase of the minority carrier lifetimes. As compared to a single ARC layer, the Ag–ZnO/ZnO double ARC layer-based Si solar cell achieved the highest conversion efficiency 14.32% with a fill factor of 81.35% at a minority carrier lifetime of 10 μs and carrier concentration of 1 × 10 17 cm −3 . The enhanced photovoltaic performance in Ag–ZnO/ZnO double ARC layer-based Si solar cells might be attributed to the high generation of electron-hole pairs, improved minority lifetime, and excellent carrier concentrations. • A simulation study was performed for optoelectrical properties of Ag–ZnO/ZnO double antireflection coating layer > Photovoltaic properties with respect to minority charge carriers/charge carrier concentrations studied > High electron and hole densities of 1.75 × 10 16 cm −3 and 1.51 × 10 16 cm −3 were observed > Ag–ZnO/ZnO double ARC layer based Si solar cell achieved the highest PCE 14.32%.

Simple interference based colorization of Si based solar cells and panels with ITO/SiNx:H double layer antireflective coatings

The integration of solar modules into buildings offers a highly attractive area for enlarging the market of commercial solar cells. Therefore, cost-effective industrial approaches to fabricate solar cells and relevant modules with different colors are required. In this work a simple method for applying individual color to Si based solar cells was adapted to the industrially fabricated commercial cells with standard SiNx:H antireflection coating (ARC) and also explicitly described by a fundamental model. This method of coloring is based on the optical interference effect in the layered structure. The structure includes a thin indium tin oxide (ITO) layer deposited on the top of the ARC. An intentional change of the ITO thickness from 0 to 240 nm resulted in a change of the color through the visible spectrum. The color was added to multi- as well as mono-Si based industrially fabricated textured solar cells with conventional blue color ARC. Reasonable agreement between the theoretical and experimental results has been obtained from the model calculations. For the proof of concept, a mini-solar-module with six green cells was fabricated that were coated by an ITO (185 nm)/SiNx:H double layer ARC stack. It is shown that the efficiency of such module is only about 1.5% lower than that of the mini-module manufactured using reference industrial cells with SiNx:H ARC only. It is concluded that the proposed approach can be considered as a cost-effective method to fabricate coloured Si based cells and relevant modules using only one simple technological step.

Damp-Heat-Stable, High-Efficiency, Industrial-Size Silicon Heterojunction Solar Cells

Summary Silicon heterojunction (SHJ) solar cells employ nanometer-thin stacks of intrinsic and doped hydrogenated amorphous silicon (a-Si:H) films as carrier-selective contacts. To achieve excellent carrier selectivity, the a-Si:H must be carefully optimized to guarantee an atomically sharp a-Si:H/c-Si interface. In this work, by combining experiments with molecular dynamics and ab initio calculations, we unveil that H atoms bonded to internal-void surfaces in a-Si:H broaden its optical band gap via a filamentary effect near the valence-band maximum. The photovoltaic performance of rear-emitter SHJ solar cells can be significantly improved by tailoring the Si−H bonding state in the front a-Si:H passivation layer, resulting in a power conversion efficiency (PCE) of 23.4% on a 6-in cell. By implementing double antireflection coatings (ARCs) of SiNx and SiOx, the PCE is further improved to 23.9%. More importantly, the ARC devices show prominently improved damp-heat stability without encapsulation in 1,000-h aging at 85°C, 85% relative humidity.

Improving the efficiency of a-Si:H/c-Si thin heterojunction solar cells by using both antireflection coating engineering and diffraction grating

In this paper, we present an analytical study of the impact of light trapping and multilayer antireflection coating (ARC) on the electrical characteristics of n(a-Si:H)/i(a-Si:H)/p(c-Si)/p+(C-Si) heterojunction solar cells with intrinsic thin layer (SHJ). The developed analytical model considers a triangular texture morphology of the solar cell top surface and a double ARC layer. This model serves as a fitness function to optimize the device reliability against the interfacial traps using Grey Wolf optimization approach (GWO). The optimized solar cell reveals a high short circuit current ISC = 47.9 mA, an open circuit voltage VOC = 0.56 V, fill factor FF = 74.72% and a conversion efficiency improvement in the order of 30% over conventional planar solar cells efficiency. Not only the optimized SHJ solar cell exhibits higher performance in terms of figure of merits, but also shows superior interfacial traps reliability at the amorphous/crystalline interface. This reliability enhancement is due to a better surface texture control and intrinsic thin film layer tuning provided by GWO approach.

Analysis of Photonic Crystal Diffraction Grating Based Light Trapping Structure for GaAs Solar Cell

The paper presents a design and quantitative analysis for an efficient light-trapping structure (LTS) based on Photonic Crystals (PhC) to enhance the performance of thin-film GaAs solar cells. LTS consists of single planar Anti-Reflection coating (ARC) layer at the top assisted by 2D PhC diffraction grating and Distributed Bragg Reflector (DBR) having alternate dielectric layers at the back of the active layer. The structure has been optically analyzed for various absorption layer thicknesses and compared with Lambertian limits, and it has been shown that with optimization of the design carefully, significant enhancement in the cell efficiency will take place for the presented LTS, especially for the devices with very thin absorption layers (typically less than 1000 nm). Further, it is demonstrated that this efficiency enhancement is attributed to the improvement in photon absorption in the wavelength range for which active layer thickness itself is not sufficient for absorption. According to the simulation analysis, the proposed cell efficiency can be enhanced 3.5 times for a 100 nm cell with LTS, and this enhancement shrinks only to 1.5 times for 1500 nm cell. The analysis has shown that for thin cells, the contribution by the optimized LTS is the main reason behind efficiency enhancement whereas the contribution from ARC remains almost constant. The evaluation of the performance of the proposed structure concerning the angle of incident light and fabrication tolerances has also been done, indicating improved performance. The paper also presents the quantitative and comparative analysis of the proposed design with different compatible designs such as a cell having double layer ARC and a cell having pyramidal ARC with PhC as BR design. Their analysis also predicts that the LTS especially BR are more important for thinner active layer cells and the cell with a pyramidal ARC with PhC outperforms the other designs.

Silicon nitride as antireflection coating to enhance the conversion efficiency of silicon solar cells

The aim of this work is to investigate the effect of single and double layer antireflection coating (ARC) on the performance of silicon solar cells. In this regard, various previous works on single and double layer ARCs have been consulted. Silicon nitride (Si 3 N 4 ) has been used as ARC material because of its varying refractive index (1.8-3.0). Numerical calculations have been performed to obtain the reflectance for single and double layer Si 3 N 4 using the transfer matrix method. Double layer antireflection coating (DLARC) of Si 3 N 4 is found to have significant advantages over single layer antireflection coating (SLARC). Calculated reflectances have been further used in the PC1D simulator as external reflectance files to study the performance of a silicon solar cell. As a result of the simulation, the reflectance is found to reduce from >30% to <2% with short circuit current of 3.86 mA/cm 2 and conversion efficiency of 20.22% for DLARC. Results obtained for DLARC were further compared with a reference cell (without ARC), a cell with SLARC, and a cell with zero reflectance on the front surface.

Low emissivity double sides antireflection coatings for silicon wafer at infrared region

Silicon wafer, when operating from the band edge to the far infrared, inherently possess nearly polarization-independent low intrinsic loss - an appropriate infrared transmission window sheet for infrared devices. However, the incident light is mostly reflected at the silicon-air interface due to large admittance mismatch. We show that the reflection of silicon wafer may be sufficiently suppressed by utilizing a double sides non-quarter wave anti-reflective coatings (ARCs). The underlying mechanism is that the interfaces of the ARCs with the silicon wafer and the air structure are selected such that the matched admittance has a real value. For an optimized double sides ARCs, we achieve a lowest light reflectance of ∼4% over a broad infrared spectral range at various light incident angles, which is superior to a single side admittance-matched ARCs. We further demonstrate that, compared with bare silicon wafer, the observed infrared normal spectral emissivity of the silicon wafer with the double sides ARCs increased by only ∼0.02. As the advantages above are not at a cost of surface modification, this structure is promising to be applied in low emissivity infrared window for radiation thermometry, sensing, and so on.

Effects of different graphene dopants on double antireflection coatings/graphene/n-silicon heterojunction solar cells

In the present work we have tested the effects of two of the most used graphene chemical dopants, nitric acid (HNO3) and thionyl chloride (SOCl2), on multilayer graphene/n-silicon (G/n-Si) Schottky barrier solar cell completed with a double antireflection coating (DARC). The DARC has been realized with a MgF2/ZnS thermal deposition on graphene. In both cases the graphene doping process performed before DARC deposition increases the graphene conductivity and the work function, leading to cells with larger open circuit voltage and higher efficiency. After DARC layer realization a second acid exposure is necessary to compensate a partial de-doping effect and restore graphene doping. However the electrical characterization shows that the DARC/G/n-Si finite solar cell behaves differently with the two dopants. It is noteworthy that the presence of DARC does not prevent a further re-doping with HNO3, allowing the fabrication of cells with 8,5% efficiency which is not the case with SOCl2: this effect was explained by different chemical interactions between graphene, the deposited DARC and the two doping substances.

Improved opto-electronic properties of silicon heterojunction solar cells with SiOx/Tungsten-doped indium oxide double anti-reflective coatings

Amorphous SiOx was prepared by plasma enhanced chemical vapor deposition (PECVD) to form SiOx/tungsten-doped indium oxide (IWO) double anti-reflective coatings for silicon heterojunction (SHJ) solar cell. The sheet resistance of SiOx/IWO stacks decreases due to plasma treatment during deposition process, which means thinner IWO film would be deposited for better optical response. However, the comparisons of three anti-reflective coating (ARC) structures reveal that SiOx film limits carier transport and the path of IWO–SiOx–Ag structure is non-conductive. The decrease of sheet resistance is defined as pseudo conductivity. IWO film capping with SiOx allows observably reduced reflectance and better response in 300–400 and 600–1200 nm wavelength ranges. Compared with IWO single ARC, the average reflection is reduced by 1.65% with 70 nm SiOx/80 nm IWO double anti-reflective coatings (DARCs) in 500–1200 nm wavelength range, leading to growing external quantum efficiency response, short circuit current density (Jsc), and efficiency. After well optimization of SiOx/IWO stacks, an impressive efficiency of 23.08% is obtained with high Jsc and without compromising open circuit voltage (Voc) and fill factor. SiOx/IWO DARCs provide better anti-reflective properties over a broad range of wavelength, showing promising application for SHJ solar cells.

Design and preparation of broadband antireflective coatings with excellent mechanical properties

Double antireflective coatings with broadband, high-transmittance and scratch-resistance properties were prepared in this research by sol-gel method. The bottom layer was the mixture of silica nanoparticles and linear silicate polymers (SiO2 NPs-LPs) obtained from base/acid two-step catalyzed tetraethyl orthosilicate (TEOS), while the top layer was the mixture of hollow silica nanoparticles and linear silicate polymers (HSiO2 NPs-LPs). By optimizing the refractive index and the thickness of the double coatings, the optical performance of the double coatings was generally consistent with the results of theoretical design. The average transmittance in the wavelength range of 400–1200nm reached 99.1%. Besides, through applying hydroxyl modification on the surfaces of silica particles and hollow spheres, the antireflective coatings exhibited excellent mechanical properties, with its pencil hardness reaching 5H and critical load for scratch being 28.9N. All these good features have made this coating promising in harsh outdoor conditions.

Environmentally-friendly, Pb-free Cu front electrode for Si-based solar cell applications

In this study, a double glass system with PbO base and ZnO base of Cu paste is designed, prepared and printed with narrow line screen printing process on polycrystalline Si solar cell which has already finished the back Al printing and deposition of double anti-reflection coatings (DARCs). And then, a two-step firing process is applied to sinter the front electrode and obtain the ohmic contact between front electrode and solar cell. The first step of firing is conducted in air atmosphere. In this process, PbO-based glass frit etched the DARCs and Ag recrystallized at the surface of Si, constructing the preliminary contact. The second step of firing is conducted in a reducing atmosphere (H2/N2 = 5/95). In this process, the CuO is reduced into Cu which is sintered with ZnO based-glass. Ag nanoparticles recrystallized in the glass layer at interface due to the interactions between H2, Ag and PbO-based glass frit and the volatility of Pb, improve the Ohmic contact between electrode and solar cell.According to our investigation, a model of the reaction mechanisms in the double glass system of Cu paste in each sintering stage is proposed. And we have shown that Ohmic contact and good sheet resistance for the Cu front electrode with Pb-free could both be obtained by applying the newly-invented Cu paste and two steps of firing process. The lowest sheet resistance and contact resistance for such a Cu front electrode measured are 0.090 Ω/□ and 0.0040 Ω/□, respectively.

Silicon nitride and intrinsic amorphous silicon double antireflection coatings for thin-film solar cells on foreign substrates

Abstract Hydrogenated intrinsic amorphous silicon (a-Si:H) was investigated as a surface passivation method for crystalline silicon thin film solar cells on graphite substrates. The results of the experiments, including quantum efficiency and current density–voltage measurements, show improvements in cell performance. This improvement is due to surface passivation by an a-Si:H( i ) layer, which increases the open circuit voltage and the fill factor. In comparison with our previous work, we have achieved an increase of 0.6% absolute cell efficiency for a 40 μm thick 4 cm 2 aperture area on the graphite substrate. The optical properties of the SiN x /a-Si:H( i ) stack were studied using spectroscopic ellipsometer techniques. Scanning transmission electron microscopy inside a scanning electron microscope was applied to characterize the cross section of the SiN x /a-Si:H( i ) stack using focus ion beam preparation.

Sol–Gel-Derived Nano-Sized Double Layer Anti-Reflection Coatings (SiO&lt;SUB&gt;2&lt;/SUB&gt;/TiO&lt;SUB&gt;2&lt;/SUB&gt;) for Low-Cost Solar Cell Fabrication

We investigate nano-sized double layer anti-reflection coatings (ARCs) using a TiO2 and SiO2 sol-gel solution process for mono-crystalline silicon solar cells. The process can be easily adapted for spraying sol-gel coatings to reduce manufacturing cost. The spray-coated SiO2/TiO2 nano-sized double layer ARCs were deposited on mono-crystalline silicon solar cells, and they showed good optical properties. The spray coating process is a lower-cost fabrication process for large-scale coating than vacuum deposition processes such as PECVD. The measured average optical reflectance (300-1200 nm) was about approximately 8% for SiO2/TiO2 nano-sized double layer ARCs. The electrical parameters of a mono-crystalline silicon solar cell and reflection losses show that the SiO2/TiO2 stacks can improve cell efficiency by 0.2% compared to a non-coated mono-crystalline silicon solar cell. In the results, good correlation between theoretical and experimental data was obtained. We expect that the sol-gel spray-coated mono-crystalline silicon solar cells have high potential for low-cost solar cell fabrication.

Influence of window layer thickness on double layer antireflection coating for triple junction solar cells

The optimization of a SiO2/TiO2, SiO2/ZnS double layer antireflection coating (ARC) on Ga0.5In0.5P/In0.02Ga0.98As/Ge solar cells for terrestrial application is discussed. The Al0.5In0.5P window layer thickness is also taken into consideration. It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.

Influence of ZnO/p+a-Si:H Microcrystallization and Antireflection Coatings on pin a-Si:H Solar Cells Performance

AbstractIn general terms this paper analyzes effectiveness of ZnO/p+/i a-Si:H/n+/Al solar cells made on commercial glass substrate with double-sided antireflection coatings. The primary topic, however, is the ZnO/p+/i a-Si:H junction based on layers obtained by the reactive magnetron sputtering (RMS) of Si:B, Si:P, Al, Zn:Al targets, where the “i” layer is a protocrystalline RFCVD layer. These single layers, as well as the respective structures, were studied using primarily Grazing Incidence X Ray Analyzes and AFM spectroscopy. In particular, the microcrystallization, surface roughness and chemical composition of the films were studied with respect to film thickness, RMS power and hydrogen dilution. The nature of the influence of ZnO/p+/i a-Si:H crystallization on pin a-Si:H solar cells performance is presented. Optical transmission and reflection measurements were used to measure the light flux reaching the “i” layer. We determined the experimentally observed angular distribution of scattered light in transmittance through glass/ZnO:Al/p+ silicon and double antireflection coatings on glass/ ZnO:Al/p+ silicon junctions. The optoelectronic properties of glass/ZnO/pin a-Si:H/Cr/Al cells are examined by systematic investigation of their I-V characteristics subsequent to steady-state conditions.

Single and double layer anti-reflection coatings for application in the infra-red region (15 μm)

New explicit expressions for computation of the single and double layer thicknesses to be used in the design of anti-reflection coatings (ARC) are presented. A theoretical study on the performance of a double layer ARC systems on Ge using ZnSe, BaF 2 and BiF 3 is presented.