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Fabrication of octagonal and dodecagonal single crystal Si micropyramids via etching without using a pre-patterned mask
摘要： Surface texturing of Si has attracted signi?cant attention over the past decades as micro/nano patterns allow for preferred opto-electronic and electrochemical properties. Here a new fabrication method, based on etching in aqueous NaOH-polyethylene glycol solution is presented, which allows the formation of novel eight and twelve sided Si micropyramids. Particularly, the presence of NaOH resulted in the formation of four sided facets along intersecting {111} planes, while with continuous etching the high molar mass polyethylene glycol resulted in the formation of four additional facets identi?ed to be (212) planes producing octagonal pyramids. Further etching of these octagonal pyramids lead to the formation of twelve-sided pyramids. Eight-faceted (octagonal) pyramids have been reported in the literature, but only through the use of photolithography, while twelve-faceted (dodecagonal) pyramids have not been observed for any type of crystal.
关键词： Pyramids,Octagon,Si patterning,Etching,Polyethylene glycol,Dodecagon
更新于2025-09-23 15:23:52
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Subwavelength-scale nanorods implemented hexagonal pyramids structure as efficient light-extraction in Light-emitting diodes
摘要： Subwavelength-scale nanorods were implemented on the hexagonal pyramid of photochemically etched light-emitting diodes (LEDs) to improve light extraction efficiency (LEE). Sequential processes of Ag deposition and inductively coupled plasma etching successfully produce nanorods on both locally unetched flat surface and sidewall of hexagonal pyramids. The subwavelength-scale structures on flat surface offer gradually changed refractive index, and the structures on side wall of hexagonal pyramid reduce backward reflection, thereby enhancing further enhancement of the light extraction efficiency. Consequently, the nanorods implemented LED shows a remarkable enhancement in the light output power by 14% compared with that of the photochemically etched LEDs which is known to exhibit the highest light output power. Theoretical calculations using a rigorous coupled wave analysis method reveal that the subwavelength-scale nanorods are very effective in the elimination of TIR as well as backward reflections, thereby further enhancing LEE of the LEDs.
关键词： subwavelength-scale nanorods,light-emitting diodes,light extraction efficiency,hexagonal pyramids,photochemical etching
更新于2025-09-23 15:21:01
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Visualizing light trapping within textured silicon solar cells
摘要： Random pyramids are the most widely used texture in commercial monocrystalline silicon solar cells to trap weakly absorbed photons with near-bandgap energies. There has been steady improvement in efforts to model the light-trapping performance of random pyramids, including a shift from an assumed pyramid base angle of 54.7° (ideal-random pyramids) to smaller values that are consistent with measured average angles. However, simulations have not yet considered the effects of a distribution of base angles (real-random pyramids), which all real textured wafers have. In this contribution, we benchmark the light-trapping capability of real-random pyramids against ideal-random pyramids and Lambertian scatterers by performing ray tracing of an accurate three-dimensional topographical map of the surface of a textured silicon wafer measured using atomic force microscopy. The angular distribution function (ADF) of light rays within the wafer, calculated at each pass as rays bounce between the front and rear surfaces, reveals that real-random pyramids are superior to ideal-random pyramids in trapping light precisely because of the distribution in their base angle. In particular, the ADF inside a wafer with real-random pyramids evolves to be Lambertian within just two passes—by the time (non-absorbed) light re-arrives at the front surface. Furthermore, the total path-length enhancement of light reaches nearly 60—exceeding that of a wafer with Lambertian surfaces—for narrow angles of incidence, though it falls short of the Lambertian reference for oblique angles.
关键词： atomic force microscopy,random pyramids,silicon solar cells,light trapping,Lambertian scatterers,ray tracing
更新于2025-09-23 15:19:57
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Nanomolded buried light-scattering (BLiS) back-reflectors using dielectric nanoparticles for light harvesting in thin-film silicon solar cells
摘要： The article presents a nanoparticle-based buried light-scattering (BLiS) back-re?ector design realized through a simpli?ed nanofabrication technique for the purpose of light-management in solar cells. The BLiS structure consists of a ?at silver back-re?ector with an overlying light-scattering bilayer which is made of a TiO2 dielectric nanoparticles layer with micron-sized inverted pyramidal cavities, buried under a ?at-topped silicon nanoparticles layer. The optical properties of this BLiS back-re?ector show high broadband and wide angular distribution of diffuse light-scattering. The ef?cient light-scattering by the buried inverted pyramid back-re?ector is shown to effectively improve the short-circuit-current density and ef?ciency of the overlying n-i-p amorphous silicon solar cells up to 14% and 17.5%, respectively, compared to the reference ?at solar cells. A layer of TiO2 nanoparticles with exposed inverted pyramid microstructures shows equivalent light scattering but poor ?ll factors in the solar cells, indicating that the overlying smooth growth interface in the BLiS back-re?ector helps to maintain a good ?ll factor. The study demonstrates the advantage of spatial separation of the light-trapping and the semiconductor growth layers in the photovoltaic back-re?ector without sacri?cing the optical bene?t.
关键词： light management,nanomolding,inverted pyramids,thin-?lm solar cells,nanoparticles,photovoltaics
更新于2025-09-23 15:19:57
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Quantum dots power polarizing light source
摘要： A new way of generating linearly polarized photons using quantum dots has been developed by an international team of researchers. The novel source of polarized light could be used to develop energy-saving computers and mobile-phone screens, as well as secure communications. Researchers have long studied quantum dots and their many possible applications, but getting them to emit photons that have a predefined polarization has proved difficult and this is an essential requirement for many applications.
关键词： quantum dots,polarized light,InGaN,gallium-nitride pyramids,indium gallium nitride
更新于2025-09-23 15:19:57
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Improved photovoltaic performance of graphene-based solar cells on textured silicon substrate
摘要： Graphene has attracted much interest as an active layer in heterojunction solar cells due to its outstanding properties such as flexibility, transparency, mechanical strength and elevated carrier mobility. In this research, a new technique was presented in order to enhance the efficiency of graphene–based heterojunction solar cells by employing a textured silicon (Si) substrate. Here, two sets of devices were fabricated based on flat and pyramidal structure of Si and the photovoltaic properties of graphene/Si heterojunction solar cells were compared. Selective chemical dissolution of Si wafers was carried out in order to produce pyramidal skeleton. Reduced graphene oxide (rGO) was then transferred on pyramidal Si through electrophoretic deposition (EPD) technique. The evidence of graphene layers on Si substrates was studied using Raman spectroscopy, X–ray diffractometry (XRD) and atomic force microscopy (AFM) analysis. The morphology of samples indicated an enhancement in rGO/Si interface area when the pyramidal structure is applied. Moreover, the enhanced surface area of this sample which is due to elevated roughness of pyramidal structure and wrinkles of graphene layers promotes its antireflective behavior which was proven using reflectance spectroscopy. The average reflectance of the graphene layer on the textured Si was ~14% in the wavelength range of 400–800 nm which is lower than that of rGO on flat Si. The improved optical properties of graphene on pyramidal silicon can broaden its potential applications in optoelectrical devices such as high-efficiency solar cells. In order to study the photovoltaic properties of rGO/Si samples, a passive layer was formed on Si substrate and a square frame of Ag was coated on it which was acted as a top contact. The current–voltage characteristics showed that the efficiency of rGO/Si heterojunction solar cells was improved when textured silicon was applied.
关键词： Schottky junction solar cell,Heterojunctions,Thin films,Reduced graphene oxide,Silicon pyramids,Electrophoretic deposition
更新于2025-09-23 15:19:57
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Numerical simulation of an ozone-based wet-chemical etching
摘要： In the PV-industry, wet-chemical baths are used for surface structuring, conditioning and cleaning. Besides cleaning the wafers, ozone-based wet-chemical cleaning processes show the ancillary effect of intendedly etching back the emitter and/or rounding of textured surfaces. To simulate and predict this rounding of micro-pyramids during the cleaning process, a two dimensional process simulation model was built. With the finite element method of COMSOL Multiphysics the diffusion and convection based mass transport of ozone along the pyramids is described. Important parameters for the evaluation, obtained from experimental results, are the etch rate and resulting roundness (R) of the micro-pyramids tips. A parametric study was carried out with the purpose of adjusting the model. The simulation represents the experimental data accurately, e.g. after 2 min exposure time R = 67 nm for the experimental and R = 66 nm for the simulation data.
关键词： PV-industry,numerical simulation,micro-pyramids,ozone-based wet-chemical etching,COMSOL Multiphysics
更新于2025-09-11 14:15:04