Inverted Pyramid Structure Research Articles

Getting Youngsters Hooked on News

Narrative news is often propagated as a means to inform and attract younger generations of news consumers. To test this, the current study assessed the effects of narrative structure versus inverted pyramid structure on information processing and news appreciation for Millennials, compared to Generation X, and Baby Boomers/Silent Generation. Participants were randomly exposed to either four online news articles written in a narrative structure or an inverted pyramid structure. Results show that people are better informed by narrative news. However, appreciation is lower for narrative news compared to the inverted pyramid. Moreover, the younger participants express lower appreciation, regardless of story structure. The results suggest that although the narrative structure is best at informing all audiences, it is not necessarily a viable strategy to attract younger news audiences.

18.87%-efficient inverted pyramid structured silicon solar cell by one-step Cu-assisted texturization technique

We achieved an inverted pyramid structure, meeting the tradeoff between the light reflection minimization and carrier recombination by adjusting the one-step Cu-assisted texturization of silicon wafer, and silicon solar cells based on this structure were fabricated, which gained a high conversion efficiency of 18.87% without using any complex techniques. These data were compared with the performance of conventional upright pyramid silicon solar cells as manufactured using identical raw wafers, the Cu-etched inverted pyramid silicon cells collected 0.59mA/cm2 more short-circuit current density and 0.47% more efficiency. Importantly, our data demonstrate the better performance and manufacturability of inverted pyramid structured silicon solar cell and as such may open new perspectives for high efficiency solar cell applications.

Freestanding carbon nanodots/poly (vinyl alcohol) films with high photoluminescent quantum yield realized by inverted-pyramid structure

Carbon nanodots (C-dots) have attracted great attention for their biocompatibility and strong tunable photoluminescence (PL). However, aggregation-induced PL quenching blocks their practical application in solid-state optoelectronics. Here, we report a luminescent C-dots freestanding film with a substantially enhanced high quantum yield (QY) of 72.3%. A facile template method, rather than complicate lithography and etching technique is proposed to fabricate the C-dots composite films with large-area (8 inch × 8 inch) ordered micro-scale inverted-pyramid patterns on the surface. The control experiment and theoretical analysis demonstrate the key success to QY enhancement lies in the separation of C-dots and the pattern of surface inverted-pyramid structure. This work realizes the QY enhancement simply by geometrical optics, not the chemical treatment of luminescent particles. It provides a general approach to fabricate large-area freestanding luminescent composite film with high QY.

Micro-structured inverted pyramid texturization of Si inspired by self-assembled Cu nanoparticles.

A superior micron-sized inverted pyramid structure has been successfully achieved by one-step copper nanoparticles assisted chemical etching in Si/Cu(NO3)2/HF/H2O2 solution for light trapping in silicon solar cells. The detailed mechanisms of such a novel method have been systematically demonstrated. The charge transfer during the reaction has been revealed by the simplified energy band diagram of the system as well. In order to form micro-structured inverted pyramids, the generation and dissolution of Cu nanoparticles should keep in balance during the reaction, which depends on the concentration of the etchant, the doping type and the doping level of the silicon substrate. With the investigation of the intrinsic properties of the silicon substrate, the etching rate is found out as a combined result of the electron concentration and the defect density of the substrate, as well as the potential barrier on the interface of Si/Cu nanoparticles. Furthermore, the anisotropic nature of Cu assisted chemical etching has also been investigated.

High efficiency multi-crystalline silicon solar cell with inverted pyramid nanostructure

In this paper, we report inverted pyramidal nanostructure based multi-crystalline silicon (mc-Si) solar cells with a high conversion efficiency of 18.62% in large size of 156×156mm2 wafers. The nanostructures were fabricated by metal assisted chemical etching process followed by a post nano structure rebuilding (NSR) solution treatment. With increasing NSR treatment time, the reflectance and the dimensions of micro oval pits were both influenced. Resulting from both the light trapping ability and passivation efficiency, 500nm inverted pyramid structure exhibited an ideal solar cell performance. The best solar cell showed a low reflectivity of 3.29% and a 0.91mAcm−2 increase of short-circuit current density, and its efficiency was 0.45% higher than the acid textured solar cell. This technique presented a great potential to be a standard process for producing highly efficient mc-Si solar cells in the future.

Texturing of monocrystalline silicon wafers by HF-HCl-H2O2 mixtures: Generation of random inverted pyramids and simulation of light trapping in PERC solar cells

Solutions containing hydrofluoric acid (HF), hydrochloric acid (HCl), and hydrogen peroxide (H2O2) were investigated as novel acidic, NOx-free etching mixtures for texturing of monocrystalline silicon wafers. High etch rates of up to 13.3nms−1 were observed at room temperature, which are comparable to the etch rates of KOH-IPA solutions. The silicon surface was investigated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), indicating pyramidal textures for diamond wire and SiC-slurry sawn as well as saw-damage etched (polished) wafers. Non-stirred baths generate random pyramidal structures while constantly stirred solutions generate novel random inverted pyramidal surface structures. The light trapping efficiency of wafers etched by the HF-HCl-H2O2 solutions was compared by UV/vis-reflectivity measurements to KOH/i-propanol specimens indicating lower reflectivities for the HF-HCl-H2O2-treated samples. Using the ‘wafer ray tracer’ (pvlighthouse.com) the light absorption properties of monomodal and random inverted pyramid structures were simulated and compared to well-known random and monomodal textures for PERC solar cells, clearly indicating the best performance for random inverted pyramids. Besides, simulation of a PERC solar cell on a roof top at our university was performed, indicating improved performance, especially for random inverted pyramid textures.

Concurrent improvement in optical and electrical characteristics by using inverted pyramidal array structures toward efficient Si heterojunction solar cells

The Si heterojunction (SHJ) solar cell is presently the most popular design in the crystalline Si (c-Si) photovoltaics due to the high open-circuit voltages (VOC). Photon management by surface structuring techniques to control the light entering the devices is critical for boosting cell efficiency although it usually comes with the VOC loss caused by severe surface recombination. For the first time, the periodic inverted pyramid (IP) structure fabricated by photolithography and anisotropic etching processes was employed for SHJ solar cells, demonstrating concurrent improvement in optical and electrical characteristics (i.e., short-circuit current density (JSC) and VOC). Periodic IP structures show superior light-harvesting properties as most of the incident rays bounce three times on the walls of the IPs but only twice between conventional random upright pyramids (UPs). The high minority carrier lifetime of the IP structures after a-Si:H passivation results in an enhanced VOC by 28mV, showing improved carrier collection efficiency due to the superior passivation of the IP structure over the random UP structures. The superior antireflective (AR) ability and passivation results demonstrate that the IP structure has the potential to replace conventional UP structures to further boost the efficiency in solar cell applications.

Wavelength-Scale Structures as Extremely High Haze Films for Efficient Polymer Solar Cells

Wavelength-scale inverted pyramid structures with low reflectance and excellent haze have been designed for application to polymer solar cells (PSCs). The wavelength-scale structured haze films are fabricated on the back surface of glass without damages to organic active layer by using a soft lithographic technique with etched GaN molds. With a rigorous coupled-wave analysis of optical modeling, we find the shift of resonance peaks with the increase of pattern's diameter. Wavelength-scale structures could provide the number of resonances at the long wavelength spectrum (λ = 650-800 nm), yielding enhancement of power conversion efficiency (PCE) in the PSCs. Compared with a flat device (PCE = 7.12%, Jsc = 15.6 mA/cm(2)), improved PCE of 8.41% is achieved in a haze film, which is mainly due to the increased short circuit current density (Jsc) of 17.5 mA/cm(2). Hence, it opens up exciting opportunities for a variety of PSCs with wavelength-scale structures to further improve performance, simplify complicated process, and reduce costs.

Fabrication of inverted pyramid structure by Cesium Chloride self-assembly lithography for silicon solar cell

Inverted pyramids were fabricated through a method combining cesium chloride (CsCl) self-assembly technology and anisotropy corrosion of silicon solar cells. Ti film with nanoporous masks was formed by lift-off the CsCl nanoislands for the inverted pyramids. The pyramids were then formed by anisotropy corrosion of alkaline solution. The average diameter and morphology of the pyramids were controlled by varying the average diameter of CsCl nanoislands from 400nm to 1.5µm and by varying the etching time of alkaline solution from 2 to 8min. The inverted-pyramid texture could suppress reflection to below 10% at wavelengths from 400 to 1000nm, which was much lower than that of planar wafer. A solar cell fabricated from the pyramids had higher short-circuit current density (Jsc) and photovoltaic conversion efficiency (PCE) compared with those of planar solar cells for the good antireflection property. The solar cell showed a PCE of 15.25%, a Jsc of 38.35mA/cm2, and an open-circuit voltage of 555.7mV.

Diamond micro engraving of gravure roller mould for roll-to-roll printing of fine line electronics

Printing electronics has attracted great attention in recent years due to its various superior performances compared with conventional silicon-based semiconductor industry. Roll-to-Roll gravure printing is able to transfer conductive nanoparticle ink onto the flexible film substrate to form continuous fine metal lines using a gravure roller mould with tens of thousands of tiny gravure cells on its surface. However, it is difficult to scale down the printed line width, which is crucial for the film's circuit density, resolution and transparency, because the market-available rollers fabricated by conventional engraving techniques for graphic printing usually have gravure cells larger than 25μm. Hence, in this study, a novel method based on ultraprecision machining technology, Diamond Micro Engraving (DME), is introduced to miniaturize the gravure cells in order to reduce the ink volume transfer during the printing process. A V-shape sharp diamond tool is used to continuously generate concave inverted micro pyramidal structures on the gravure roller surface using the Slow Slide Servo technology. Geometrical modelling of the engraving process is conducted to help programming the tool path to realize accurate control of the instantaneous position of two linear axes and one rotatory axis. Through applying the DME process, generation of consistent cell structure is achieved. The engraved gravure cell width is successfully miniaturized to 7μm. With the optimized cell spacing value, the DME-machined roller moulds are used in gravure printing of metal mesh film, which works as a potential transparent conductive film to replace the expensive indium-tin-oxide (ITO). The printed line width is reduced from 47μm to 19μm, and the transmittance of the printed metal mesh film for visible light is increased from 65.2% to 80.4% accordingly, which is comparable to the transmittance of ITO film.

News Writing for Print

A good print news story will contain the following components: inverted pyramid structure, five Ws and H, leads, impersonal reporting, news writing techniques, quotations and attributions, Associated Press Style, and proper grammar and punctuation. This 5-page fact sheet was written by Ricky Telg, and published by the UF Department of Agricultural Education and Communication, January 2015. AEC529/WC191: News Writing for Print (ufl.edu)

Optical inspection of solar cells using phase-sensitive optical coherence tomography

The inspection and measurement of solar cells has become an important technique in evaluating the efficiency and quality of solar cell devices. Currently, surface defect detection of solar cells can be achieved by several approaches such as machine vision, photoluminescence, and electroluminescence imaging techniques. Nevertheless, it is still difficult to inspect the inner structures of solar cells. In response to this need, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have become common techniques for investigating the nanostructures of solar cells. However, both carry the disadvantages of destructive imaging, high cost, and a small inspection area. Moreover, it is difficult to simultaneously estimate multiple optical properties with the aforementioned techniques.In this study, we propose the use of phase-sensitive optical coherence tomography (PS-OCT) for the inspection of solar cells. We develop a two-reference-arm configuration to reduce the phase noise that intrinsically accompanies the OCT system. Based on the proposed approach to extract the amplitude and phase terms from OCT interference signals, the 3D microstructure of solar cells can be obtained while simultaneously probing the nanostructures on arbitrary planes of the solar cell. The OCT microstructural results show that the structures of different layers can be nondestructively visualized and quantitatively evaluated. From the phase signal, the inverted pyramid structure, which is commonly used for the reduction of interface reflection, can be visualized. Moreover, based on the two-reference-arm configuration, the optical reflection coefficient (ORC) can be estimated in order to evaluate the interface reflection from the surface of solar cell. Results show that PS-OCT can be a valuable tool for providing nondestructive inspection of the micro/nanostructures of solar cells.

Using nanoimprint lithography to improve the light extraction efficiency and color rendering of dichromatic white light-emitting diodes.

Despite the efficiency of gallium nitride (GaN)-based blue light-emitting diodes (LEDs), the light extraction arising from the packaging of the phosphor remains an important issue when enhancing the performance of dichromatic white LEDs. In this study, we employed a simple, inexpensive nanoimprinting process to increase both the light extraction efficiency and color rendering of dichromatic white LEDs. We employed the rigorous coupled wave approach (RCWA) to optimize the light extraction efficiency of yellow and blue light. We found that the presence of the light extracting structures could also improve the color rendering of the dichromatic white LEDs, due to the different light extraction efficiencies of the textured structures at different wavelengths. After fabricating inverted pyramid structures on the surface of the encapsulation layer, the intensity of the blue light at 455 nm increased by 20%. When we further considered the color rendering and correlated color temperature (CCT), the enhancement of blue light was 15% and that of yellow light was 4%. Meanwhile, the light extraction of the intensity dip near 490 nm was enhanced significantly (by 25%), resulting in an increased dip-intensity of light at 490 nm relative to the intensities of the blue and yellow light. Accordingly, the color rendering index (CRI) of this dichromatic white LED increased from 69 to 73. Because it improved both the light extraction efficiency and color rendering of dichromatic white LEDs, this simple method should be very helpful for enhancing their applications in solid state illumination.

Carbon nanotubes film preparation on 3D structured silicon substrates by spray coating technique for application in solar cells

This paper firstly reports the preparation of carbon nanotubes (CNTs) film on silicon substrate of three-dimensional (3D) inverted pyramid structure (IPS) by spray coating. The effect of different substrate temperatures, spraying times and opening sizes on CNTs sidewall covering properties were investigated. The results show that the CNTs covering ratio of sidewall is much lower than that of flat surface and gradually decrease with depth. 40μm×40μm opening obtained the best sidewall covering by CNTs suspension of 40μg/ml at 120°C after 30min spraying so that the CNTs can reach the bottom of IPS and cover about 68.9% sidewall area. At last, it is demonstrated that the output power of the CNTs film-Si solar cell can be enhanced 5.7 times by this method compared to that of the plane structure.

Electronic structures of GeSi nanoislands grown on pit-patterned Si(001) substrate

Patterning pit on Si(001) substrate prior to Ge deposition is an important approach to achieve GeSi nanoislands with high ordering and size uniformity. In present work, the electronic structures of realistic uncapped pyramid, dome, barn and cupola nanoislands grown in {105} pits are systematically investigated by solving Schrodinger equation for heavy-hole, which resorts to inhomogeneous strain distribution and nonlinear composition-dependent band parameters. Uniform, partitioned and equilibrium composition profile (CP) in nanoisland and inverted pyramid structure are simulated separately. We demonstrate the huge impact of composition profile on localization of heavy-hole: wave function of ground state is confined near pit facets for uniform CP, at bottom of nanoisland for partitioned CP and at top of nanoisland for equilibrium CP. Moreover, such localization is gradually compromised by the size effect as pit filling ratio or pit size decreases. The results pave the fundamental guideline of designing nanoislands on pit-patterned substrates for desired applications.

Investigation of surface features for 17.2% efficiency multi-crystalline silicon solar cells

Maskless reactive ion etching (RIE) texturing using a gas mixture of sulfur hexafluoride–oxygen (SF6/O2) and sulfur hexafluoride–oxygen–chlorine (SF6/O2/Cl2) was investigated to reveal the proper shape in surface features for higher efficiency multi-crystalline silicon (mc-Si) solar cells; hence, needle-like and round-top cone (RT cone) shapes were formed by RIE texturing with SF6/O2 gas, and pyramid and inverted pyramid shapes by RIE texturing with SF6/O2/Cl2 gas. RIE-textured mc-Si solar cells were fabricated on these surface features except for an inverted pyramid structure in the industrial production line. Performances of cells with RT cone and pyramid shapes were enhanced, whereas those with a needle-like cone were degraded, compared to the reference cells. Among these cells, those with RT cones represented the highest efficiency at 17.22%. By considering diode characteristics and electroluminescence images of fabricated solar cells, the proper shape for surface features was intimately related to control of the formation of a stable emitter layer as well as the reduction of surface reflectance.

Width-dependent interaction of trench-like microdischarges arranged in sub-arrays on a single silicon-based chip

Multiple trench microdischarge reactor arrays based on a silicon (Si) platform were investigated as a concept to overcome production-based errors. The devices incorporated four sub-arrays of trench-like anisotropically etched cavities on a single 2 cm × 2 cm Si chip. Each sub-array consisted of an equal number of structures of equal length, depth and separation only varying in trench width. Experiments were performed in argon (Ar) close to atmospheric pressure at ac frequencies of the order of 10 kHz. The arrays were characterized by means of electrical measurements and by (phase-resolved) optical emission. It is shown that the whole device as well as the independent sub-arrays and the individual cavities behave in a similar way as the inverted-pyramid structures investigated beforehand. Under identical conditions, the voltage required for a first ignition increases with the width of the cavities. For maximum voltages high enough for operation of all sub-arrays, the individual arrays ignite within the excitation period in reverse order. For different excitation frequencies, self-pulsing and emission waves propagating independently across the sub-arrays were observed. Both phenomena show distinct characteristics for the individual sub-arrays being more prominent for the smaller cavities. The observations are interpreted within the frame of a simple physical picture, as a field and a surface-dependent process and the influence of long-living species such as metastables.

Micromolding Surface‐Initiated Polymerization: A Versatile Route for Fabrication of Coatings with Microscale Surface Features of Tunable Height

This article introduces a process termed micromolding surface‐initiated polymerization (μMSIP) as a versatile route to provide surface‐bound, partially fluorinated polymer coatings with a homogeneous array of microscale surface features. The process employs hard‐polydimethylsiloxane (h‐PDMS) to mold the surface structure of master substrates exhibiting patterned microscale features. Upon filling the mold with the monomer 5‐(perfluorooctyl)norbornene (NBF8) and placing against a surface that is pre‐activated for surface‐initiated ring‐opening metathesis polymerization (SI‐ROMP), a partially fluorinated polymer film propagates from the surface with features that grow into the recesses of the mold to produce the final microtextured coating. The heights of these features can be tuned from 20–100% of the full height of the mold features based on the amount of initiator employed as well as the polymerization time and temperature. Reproduced topographies include pyramidal and inverted pyramidal structures. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images show that the final polymer film exhibits a homogeneously microstructured surface that resembles that of its corresponding master.

Inverted nanopyramid texturing for silicon solar cells using interference lithography

We report on a maskless and scalable technique for fabricating nano-scale inverted pyramid structures suitable for light management in crystalline silicon solar cells. This technique utilizes interference lithography and subsequent combined dry and KOH wet pattern transfer etching techniques. The inverted nanopyramid structures suppress the total reflection at normal incidence to below 10% over the entire visible range. The overall efficiency of the solar cell has been increased by 67% with the inverted nanopyramid texturing. The standard dual MgF2/ZnS anti-reflection coating further enhanced the overall efficiency by 5.79%.

Natural substrate lift-off technique for vertical light-emitting diodes

Hexagonal inverted pyramid (HIP) structures and the natural substrate lift-off (NSLO) technique were demonstrated on a GaN-based vertical light-emitting diode (VLED). The HIP structures were formed at the interface between GaN and the sapphire substrate by molten KOH wet etching. The threading dislocation density (TDD) estimated by transmission electron microscopy (TEM) was reduced to 1 × 108 cm−2. Raman spectroscopy indicated that the compressive strain from the bottom GaN/sapphire was effectively released through the HIP structure. With the adoption of the HIP structure and NSLO, the light output power and yield performance of leakage current could be further improved.