Pyramidal Texture Research Articles

Fabrication of light trapping structures specialized for near-infrared light by nanoimprinting for the application to thin crystalline silicon solar cells

Vehicle-integrated photovoltaics (VIPV) are gaining attention to realize a decarbonized society in the future, and the specifications for solar cells used in VIPV are predicated on a low cost, high efficiency, and the ability to be applied to curved surfaces. One way to meet these requirements is to make the silicon substrate thinner. However, thinner substrates result in lower near-infrared light absorption and lower efficiency. To increase light absorption, light trapping structures (LTSs) can be implemented. However, conventional alkali etched pyramid textures are not specialized for near-infrared light and are insufficient to improve near-infrared light absorption. Therefore, in this study, as an alternative to alkaline etching, we employed a nanoimprinting method that can easily fabricate submicron-sized LTSs on solar cells over a large area. In addition, as a master mold fabrication method with submicron-sized patterns, silica colloidal lithography was adopted. As a result, by controlling silica coverage, diameter of silica particles (D), and etching time (tet), the density, height, and size of LTSs could be controlled. At the silica coverage of 40%, D = 800 nm, and tet = 5 min, the reduction of reflectance below 65% at 1100 nm and the theoretical short-circuit current gain of 1.55 mA/cm2 was achieved.

Comparison of random upright pyramids and inverted pyramid photonic crystals in thin crystalline silicon solar cells: An optical and morphological study

The potential of enabling a wide range of applications with lightweight, flexible, thin silicon photovoltaic (PV) devices has led to research interest in various light-trapping technologies for thin silicon absorbers. Herein, using both experiments and photonic modelling, we present a detailed comparison between random pyramid texturing and inverted pyramid photonic crystal patterning in thin silicon vis-à-vis light trapping. In particular, we investigate the potential of uniform single-dimension periodic structures in contrast to conventional multi-dimensional random structures for high broadband absorption efficiency in ultra-thin silicon. We find that inverted pyramid photonic crystals cause a large increase in optical path length especially for long wavelength photons due to strong wave interference producing exceptionally high absorption and so does random pyramids though with slightly lower absorption than that of photonic crystals. On the other hand, the random pyramids, fabricated via a one-step etching process with feature sizes ranging from sub-micron to 4 µm, have higher absorption at short wavelengths due to their multi-dimensional size distribution. Overall, we find that random textured pyramids appropriately fabricated can yield a comparable ideal photocurrent density to that by photonic crystals for 10 µm thick silicon.

Chain pyramid texturization for better light trapping and efficiency of silicon solar cells

Chain pyramid texturization for better light trapping and efficiency of silicon solar cells

Nanopatterned SiNx Broadband Antireflection Coating for Planar Silicon Solar Cells

Crystalline Si solar cells based on thin wafers, with thicknesses in the range of 5–50 μm, can find applications in a wide range of markets where flexibility and bendability are important. For these cells, avoiding standard macroscopic texture is desirable to increase structural integrity. Herein, a nanopatterned SiN x antireflection (AR) coating that consists of 174 nm‐radius and 118 nm‐high SiN x nanodisks arranged in a square lattice on a thin (59 nm) SiN x layer is introduced. This geometry combines Fabry–Pérot AR and forward scattering by a resonant Mie mode to achieve high transmission into the Si absorber over a broad spectral band. The nanostructured coating is patterned on a commercial interdigitated‐back‐contact (IBC) Si solar cell, experimentally demonstrating a short‐circuit current density (J sc) of 36.9 mA cm−2, 2.3 mA cm−2 higher than for a single‐layer AR coated cell, and an efficiency of 16.3% at a thickness of around 100 μm. It is shown that light incoupling efficiency is comparable to that of pyramidal texturing, while the absorption in the infrared is lower, due to less‐effective light trapping. Overall, nanopatterned SiN x broadband AR coatings are an appealing option for improving light management in ultrathin solar cells and other optoelectronic devices.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Highly Efficient Perovskite Solar Cells with Light Management of Surface Antireflection

Abstract Perovskite solar cells (PSCs) captivate tremendous interest thanks to high-efficiency and low-cost. Nevertheless, the planar PSCs are negatively affected by serious reflection loss usually because of the refractive index mismatch between the glass substrate and the air, which limits their light harvesting performance. Here, we report an investigation for highly efficient PSCs with light management by applying a structural antireflective film made of polydimethylsiloxane (PDMS) pyramidal texture. Machine learning is firstly used to predict planar (FAPbI3)0.95(MAPbBr2.2Cl0.8)0.05 PSC’ performance for an experimental guide. The experimental results show excellent agreement between the two. When the antireflective film is utilized in the present planar PSCs, an impressive light absorption enhancement is achieved, resulting in a significantly increased power conversion efficiency of up to 23.5%.

Surface Engineering in SnO2/Si for High-Performance Broadband Photodetectors

Silicon-based photodetectors are important optoelectronic devices in many fields. Many investigations have been conducted to improve the performance of silicon-based photodetectors, such as spectral responsivity and sensitivity in the ultraviolet band. In this study, we combine the surface structure engineering of silicon with wide-bandgap semiconductor SnO2 films to realize textured Si-based heterojunction photodetectors. The obtained SnO2/T-Si photodetectors exhibit high responsivity ranging from ultraviolet to near-infrared light. Under a bias voltage of 1 V, SnO2/T-Si photodetectors (PDs) with an inverted pyramid texture show the best performance, and the typical responsivities to ultraviolet, visible, and near-infrared light are 0.512, 0.538, 1.88 (800 nm, 67.7 μW/cm2) A/W@1 V, respectively. The photodetectors exhibit short rise and decay times of 18.07 and 29.16 ms, respectively. Our results demonstrate that SnO2/T-Si can serve as a high-performance broadband photodetector.

Monolithic perovskite/black-silicon tandems based on tunnel oxide passivated contacts

<h2>Summary</h2> Perovskite/silicon tandems offer a promising pathway to increase the efficiency beyond the Auger limit of silicon at minimal additional cost. However, it is challenging to accommodate the solution-processed perovskite without flattening or reducing pyramidal texture of silicon subcells. Herein, we report the first monolithic perovskite/silicon tandem featuring an industrially applicable front-side-nanostructured black silicon with a tunnel oxide passivated contact (TOPCon). The TOPCon together with the surface reconstruction of black silicon contributes to the high-level surface passivation without sacrificing the broadband light trapping. Additionally, the reconstructed nanotexture significantly facilitates the wetting of perovskite and acts as a nanoconfining scaffold to guide the vertical growth of perovskite. The resulting tandem yields a certified efficiency of 28.2%, representing one of the highest efficiencies reported on either perovskite/TOPCon or double-side-textured perovskite/silicon tandems.

Influence of an Anti-Reflective Coating (ARC) with a pyramidal texture on a Building Integrated low-Concentration Photovoltaic (BICPV) system

Photovoltaic solar energy brings a new opportunity to reduce electricity generation costs and the emission of greenhouse gases. This generation has positioned itself as the most important for renewable energies, mainly because of its impact on generation at an industrial scale. However, in the residential sector, different strategies are proposed within the framework of the best use of the available area to reduce costs, as is the case of low-concentration photovoltaic systems. This document presents an Anti-Reflective Coating (ARC) with a pyramidal texture in two dimensions, for a V-Trough type photovoltaic concentrator, specifically for a Building Integrated low-Concentration Photovoltaic (BICPV) system to increase the light capture avoiding the energy loss caused by the rays coming from incidence angles different from the normal surface. For this, the authors propose a design methodology for the concentrator, determining the material and the geometry of the texture for the ARC and ray tracing simulations and experimentation validate the whole assembly. Finally, electrical generation data is taken in real-time, and it is observed how this texture's application positively affects the photovoltaic system's generation, increasing the normalized efficiency by more than 3 %.

Nanopyramid Texture Formation by One‐Step Ag‐Assisted Solution Process for High‐Efficiency Monocrystalline Si Solar Cells

In monocrystalline Si solar cells, pyramidal surface textures with the size of a few micrometers (micropyramids) are commonly applied for light in‐coupling and trapping. Recently, there is a growing need to reduce the size of pyramids below 1 μm. Herein, an original method to fabricate nanometer‐sized pyramids (nanopyramids) featuring an average size of ≈500 nm or even smaller by using a simple one‐step Ag‐assisted solution process is proposed. The texture size can be controlled by the concentration of AgNO3 in the alkaline etching solution where the generated Ag nanoparticles act as an etching mask as well as promoting the detachment of H2 bubbles from the reacting Si surface. This process enables the formation of uniformly distributed Si nanopyramids with a lower reflectance below 10% and a smaller etching margin less than 1.7 μm compared with the conventional micropyramids. Silicon heterojunction solar cells employing Si nanopyramids outperform those with the conventional micropyramids owing to the reduced optical reflectance while preserving excellent surface passivation and carrier transport properties. These results demonstrate the advantages of our method and the high potential of Si nanopyramids for various applications such as thin crystalline Si solar cells and perovskite/Si tandem solar cells.

Comprehensive cell to module optical loss analysis of metal assisted chemically etched inverted pyramid textured multi-crystalline silicon solar cells and modules by ray-tracing method

Most of the recent articles addressing the texturing issues of diamond wire sawn multi-crystalline silicon (mc-Si) wafers propose metal-assisted chemical etching (MACE) inverted pyramid texturing scheme as the best suited industrial process for the fabrication of low-cost, high efficiency solar cells. However, a detailed generation loss analysis of such textured solar cells are not widely investigated yet, especially after module conversion. We present a comprehensive analysis of various optical losses in MACE inverted pyramid textured mc-Si solar cells and modules using the SunSolve module ray-tracer simulator from PV Lighthouse. The simulation model accurately predicted the optical properties of MACE inverted pyramid textured samples and the simulated reflectance values were nearly identical to experimentally measured values at different stages of solar cell processing (before and after ARC). This study quantifies and benchmarks the optical generation losses of not-encapsulated and encapsulated inverted pyramid textured cells with well established models of random pyramid textured and iso-textured solar cells for aluminum back surface field (Al-BSF) architecture. Moderate cell to module (CTM) generation current loss was noticed for inverted pyramid textured solar cells, which was nearly 0.71 mA-cm−2 lower than random pyramid textured and 1.05 mA-cm−2 higher than iso-textured solar cells. We find that adoption of MACE inverted pyramid texturing over acid texturing enhances the photo-generation in mc-Si modules by ∼0.5% and that the total photo-generation current density in mc-Si solar modules approach 99.6% of that in random pyramid textured c-Si modules.

A comparative study on the microstructure, texture, and mechanical properties of extruded Mg–9Li and Mg–9Li-0.3Ca alloys

The microstructure, texture and mechanical response of extruded Mg–9Li and Mg–9Li-0.3Ca were examined. The results indicated that the Ca addition resulted in the formation of micro-sized Mg2Ca and a reduction in volume fraction of α phase. Besides, compared with Mg–9Li, Mg–9Li-0.3Ca exhibited a higher degree of dynamic recrystallization (DRX) and a lower volume fraction of subgrains, which are mainly attributed to the particle stimulated nucleation (PSN) effect and stacking fault energy (SFE) reduction caused by Ca addition. Texture analysis results demonstrated that both {0002}<10 1‾ 0> basal texture of α phase and α-fiber texture of β phase were weakened with Ca addition, whilst it was reversed for the {11 2‾ 2}<1‾1‾ 23> pyramidal texture of α phase. Finally, under the synergistic action of microstructure and texture alterations induced by Ca addition, Mg–9Li-0.3Ca displayed a higher elongation (EL) and strain hardening capacity while a lower yield strength (YS) and ultimate tensile strength (UTS) than Mg–9Li in tension along extrusion direction (ED).

Microstructure and mechanical behavior of Ti/Cu/Ti laminated composites produced by corrugated and flat rolling

Ti/Cu/Ti laminated composites were fabricated by corrugated rolling (CR) and flat rolling (FR) method. Microstructure and mechanical properties of CR and FR laminated composites were investigated by scanning electron microscopy, numerical simulation methods, peel and tensile examinations. The effect of CR and FR was comparatively analyzed. The results showed that the CR and FR laminated composites exhibited different effective plastic strain distributions of the Ti layer and Cu layer at the interface. The recrystallization texture, prismatic texture and pyramidal texture were developed in the Ti layer by CR, while the R-Goss texture and shear texture were developed in the Cu layer by CR. The typical deformation texture components were developed in the Ti layer and Cu layer of FR laminated composites. The CR laminated composites had higher bond strength, tensile strength and ductility.

Finite difference time domain simulations of absorption enhancement in thin GaAs solar cells with textured back surface reflectors

Three-dimensional finite difference time domain simulations were performed to evaluate the absorption enhancement of near-band edge light in 500 nm-thick GaAs solar cells with textured rear reflectors. Three types of the textures were examined: Triangular-prisms, pyramids, and a pseudo-random etch. The tested design parameters were the period and aspect ratios of the texture and then the thickness of the transparent rear scattering layer. It was found that a low-index layer between semiconductor and metal was required to achieve a high degree of absorption enhancement, as this layer greatly reduced parasitic absorption in the metal reflector. In terms of absorption enhancement, pyramids of nearly any period and aspect ratio were superior to triangular prisms by a factor between 2 and 3. The pseudo-random etch achieved performance generally between the two other texture types. The most promising texture in terms of feasibility and performance was pyramids with a period of 2 µm and aspect ratio of 0.3, as this texture is accessible to wet-etching and granted especially high absorption enhancement. A cell thusly textured achieved 1-sun terrestrial short-circuit current of 27.4 mA/cm 2 compared to 28.3 mA/cm 2 for a conventional, 3 µm-thick on-substrate cell. Current loss was due to parasitic absorption and light escaping through the front surface. • Textured rear reflectors allow GaAs solar cell active region to be thinned. • Thin GaAs cells thus far struggle to reach predicted performance. • Thins cells with back surface reflector textures were simulated and optimized. • Optimized pyramid textures demonstrated absorption enhancement factors of about 20.

Degradation of differently processed Mg-based implants leads to distinct foreign body reactions (FBRs) through dissimilar signaling pathways

Mg alloys have mechanical properties compatible with human bones. However, their rapid degradation and associated foreign body reactions in vivo significantly limit their application for human implants. In this study, three differently processed Mg alloys, pure Mg (PM), cold extruded Mg alloy AZ31 (CE AZ31), and fully annealed AZ31 Mg alloy (FA AZ31) were comparatively investigated for their potential as implants using a rat model. All three implanted Mg alloys do not show any impact on hepato- and renal function, nor any signs of observable changes to vital organs. Proteomics analysis of tissues directly contacting the implants 2.5 months post implantation revealed that FA AZ31 activates very few inflammation and immune associated signaling pathways; while the CE AZ31 and PM produce more significant inflammatory responses as confirmed by cytokine array analyses. Further, FA AZ31 activated pathways for cell organization and development that may improve the recovery of injured tissues. Structurally, EBSD analysis reveals that the FA AZ31 alloy has a higher ratio of first-order pyramidal orientated (10–11){10–1–2} grain texture with a value of 0.25, while PM and CE AZ31 alloys have lower ratios of first-order pyramidal orientated texture with the values of 0.16 and 0.17, respectively. This is associated with recovery and recrystallisation during annealing which promotes grain texture which exhibits enhanced degradation behaviours and induces a more limited immune response in vivo. In conclusion, the FA AZ31 demonstrated better biocompatibility and corrosion resistance and is a promising candidate for metal-based degradable implants which warrants further investigation.

Influence of Silicon Substrate Surface Finish on the Screen‐Printed Silver Metallization of Polysilicon‐Based Passivating Contacts

Passivated contact based on a thin interfacial oxide and a highly doped polysilicon layer has emerged as the next evolutionary step to increase the efficiencies of industrial silicon solar cells. To take maximum advantage from this layer stack, it is vital to limit the losses at the metal polysilicon interface, which can be quantified as metal polysilicon recombination current density (J0met) and contact resistivity. In cell concepts, wherein a large variety of silicon substrate surface finish can be obtained, it is essential to know how the surface finish affects theJ0metand contact resistivity. Herein, commercially available fire through silver paste and the metal‐polysilicon recombination current densities and contact resistivity are used for three different silicon substrate surface finishes, namely: planar or saw damage etched (SDE), chemically polished in acidic solution and alkaline pyramidal textured. Contact resistivity values below 3 mΩ cm2withJ0metin order of the recombination current density of the doped region (J0pass) are obtained for samples with planar surface for both 150 and 200 nm n+polysilicon layer thicknesses. The results presented in this work show that the samples with flat substrate morphology outperform the samples with textured surfaces.

Ultrafast Random‐Pyramid Texturing for Efficient Monocrystalline Silicon Solar Cells

Herein, an ultrafast random‐pyramid texturing process is proposed for monocrystalline silicon (mono‐Si) solar cells by combining metal‐catalyzed chemical etching (MCCE) and the standard alkaline texturing process. Namely, large numbers of artificial defects are introduced on the wafer surface in 3 min by MCCE; therefore, the process duration of alkaline texturing is largely shortened from 420 s for the as‐cut wafer to 180 s for the wafer with artificial defects due to its high surface reactivity. Moreover, those tiny artificial defects are apt to form small pyramids, resulting in a better light‐trapping performance. As a demonstration, the passivated emitter rear contact solar cell with ultrafast random pyramid texture achieves a power conversion efficiency of 23.02%. Therefore, such a cost‐effective ultrafast texturing strategy can open a promising new route toward the mass production of high‐efficiency industrial mono‐Si solar cells.

Surface texturisation for the reduction of light reflection in ZnO/Si heterojunction

ABSTRACT In this paper, the impact of pyramidal texture on a silicon substrate in ZnO/p-Si heterojunction was investigated. The texturisation of p-type silicon (100) substrate was obtained using the KOH anisotropic wet chemical etching method for different etching times. The RF magnetron sputtering technique was used to deposit ZnO thin films on textured Si substrates and planar Si substrates to form ZnO/Si heterojunction. The surface morphology was studied with field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Optical properties were investigated using UV-Visible spectroscopy and photoluminescence (PL). The results show that the PL intensity in the visible region of the electromagnetic spectrum increases with the etching time, while a significant reduction is observed in the reflectance. Due to impressive anti-reflection response, ZnO/Si (textured silicon-TS) heterojunction can be effective in improving the efficiency of solar cells.

Improved Interfacial Contact for Pyramidal Texturing of Silicon Heterojunction Solar Cells.

Reducing the surface reflectivity of silicon substrates is essential for preparing high-performance Si-based solar cells. We synthesized pyramid-nanowire-structured Si (Si-PNWs) anti-reflection substrates, which have excellent light-trapping ability (<4% reflectance). Furthermore, diethyl phthalate (DEP), a water-insoluble phthalic acid ester, was applied to optimize the Si-PNWs/PEDOT:PSS interface; the photoelectric conversion efficiency of heterojunction solar cells was shown to increase from 9.82% to 13.48%. We performed a detailed examination of the shape and optical characteristics of Si-PNWs, as well as associated photoelectric performance tests, to investigate the origin of performance improvements in Si-PNWs/PEDOT:PSS heterojunction solar cells (HSCs).

Analysis of Spectral Transmission in Si Solar Cell with Pyramidal Texturization by Using PC3S Simulation

Management of light is a crucial task in solar cell design and structure because it increases the path length of the light inside, which in turn increases the probability of electron-hole pair generation. This study addresses the impact of a pyramidal textured structure on spectral transmission in the morphology of silicon. The morphology of silicon wafers was investigated using PC3S spectral transmission software to study the spectral transmission, reflectance, collection probability, mobility, carriers, electric field, velocity, current and surface recombination. Spectral transmission on the front surface with pyramidal texture showed a better transmission percentage than the planar surface. The texture with a depth of 20 μm and base length of 20 μm exhibited good performance in front spectral transmission, spectral reflectance, electric field, velocity, current and surface recombination from the top to the bottom of the sample. The planar surface had more reflectance and lower collection probability than the other pyramidal textured samples due to its low mobility, carriers, electric field, velocity and current but high surface recombination.