Figure 8: Reflectance spectra from fabricated SNCs: calculated (blue) and measured (red).
We have reviewed recent advances in various siliconnanostructures used for antireflection and light trapping in crystalline silicon solar cells, such as nanopyramids, nanopillars, nanocones, and nanoparaboloids, with particular focus on the fabrication techniques, the structural parameters and the resulting performance. Using the transfer matrix method, we have simulated and optimized three silicon nanostructure shapes and found that nanocones and nanoparaboloids outperform nanopillars. They exhibit nearly the same antireflective performance, reducing the average reflectance of the crystalline silicon surface below 2% in the wavelength range 300-1100 nm and under normal incidence. Our simulation and optimization results showed that with these two silicon nanostructure shapes short-circuit current densities of 41.62 and 41.96 mA/cm² can be expected, respectively. Therefore, this is a confirmation of the great potential of these nanostructures to enhance the power conversion efficiency of crystalline silicon solar cells. We have fabricated a conical AR nanostructure by MACE method and measured its average reflectance. We have noticed a small deviation in the average reflectance between the measured (2.96%) and the calculated one (1.98%).
The presence of a Localized Surface Plasmon Resonance in doped semiconductor nanostructures opens a new field for plasmonics and metasurfaces. Semiconductor nanostructures can be easily processed, have weak dissipation losses, and the plasmon resonance can be tuned from the mid- to the near-infrared spectral range by changing the dopant concen- tration (in complement to the constituent material, the size and shape of the nanostructure). We present in this paper an extension of the Green Dyadic Method applied to the case of doped siliconnanostructures of arbitrary shape on a planar silica substrate. The method is used to compute both far- and near-fied optical properties, such as the extinction efficiency and the electromagnetic near-field intensity inside and around any doped silicon nanostructure, respectively. This theoretical approach provides an important tool for active dopant characterization in doped semiconductor nanos- tructures, for near-field imaging of complex nanoantennas produced by electron beam lithography, and for the definition of doped semiconductor-based metasurfaces.
carriers created by the energetic photons of the solar spectrum give rise to the emission of two photons having a lower energy. Unfortunately, detrimental eﬀects such as Auger recombination and/or intraband relaxation reduce drastically the eﬃciency of the process and consequently do not favor an increase in the solar cell yield. To enhance the absorption range of the solar spectrum, the cell structure has been adapted, giving rise to the tandem cell structure. This consists in stacking layers of diﬀerent materials absorbing diﬀerent parts of the solar spectrum. The use of amorphous silicon (a-Si) in a multi-junction solar cell/tandem cell has been the most popular choice over the years. Diﬀerent junction devices with appropriately graded bandgaps can be placed in a stack to form a multi-junction device. The top junction absorbs the higher-energy photons and transmits the lower-energy photons to be absorbed by the bottom junctions. In the 1980s, remarkable advancements were made in the study of amorphous Si (a-Si)- based structures like silicon carbide, silicon nitride, etc. It has been demonstrated that the multi-junction tandem structures of a-Si such as a-SiC/a-Si heterojunctions as well as a-Si/poly-Si and a-Si/Ge alloys 40 could result in a stable multi-junction with reduced light-
where 𝑐 is the specific heat and 𝜌 is the density of the material. Therefore, to evaluate the thermal conductivity, both density and specific heat should be known, which is challenging for nanostructured materials.
Often, the density and the specific heat for nanostructures are considered to be the same as for the bulk state 13,14 . However, this assumption is crude, since changes in phonon dispersion and influence of phonon surface modes can affect the specific heat 15 . Generally, features of the structure determine the application of the assumptions 16 , while a universal approach applicable for all case does not exist. Consequently, the development of new methods for the thermophysical properties study of nanostructured materials remains an important issue.
The ubiquitous silicon microelectronics “chip” is taken for granted in modern society. There has been much research involved in producing these high technology marvels and such research continues unabated at a faster and faster pace. Despite the often stated announcement that “the age of GaAs has arrived”, it never quite has, and continued developments in Si and, more recently, Si 1-x Ge x alloy/strained Si technology (1-3) continue to advance the frontiers of microminiaturization, complexity, and speed. This continued advance has been driven by application requirements in switching technology (e.g., computers) and high-speed electronics (e.g., wireless telecommunications). Gallium arsenide and other compound semiconductors have, however, maintained a significant role in the construction of optoelectronic and purely photonic devices where the medium of switching and communication is light itself (4).
ABSTRACT: Silicon is essential in several energy-related devices, including solar cells, batteries and some electrochemical systems.
These devices often rely on micro- or nanostructures to function efficiently, and require patterning of metallic surfaces. Currently, constructing silicon features at the micro- and nanoscale requires top-down energy-intensive processes, such as e-beam lithography, chemical etching or anodization. While it is difficult to form silicon in aqueous solution, its oxide, silica, can easily be synthesized using sol-gel chemistry and nucleated onto templates with diverse shapes to create porous or continuous architectures. Here, we demonstrate that novel silica nanostructures can be synthesized via biomineralization, and that they can be reduced to silicon using magnesiothermal reduction. We selected three biotemplates to create silica structures with various aspect ratios and length scales. First, we use diatomaceous earth as a model silica material to optimize our process, and we also biomineralize silica onto two micro- organisms, the high aspect ratio M13 bacteriophage, and the helical Spirulina major algae. During our process, the shape of the materials is preserved, resulting in silicon nanowires, nano-porous networks, spirals and other micro- and nano-structures with high surface area. Our method provides an alternative for the creation of siliconnanostructures, using pre-formed silica synthesized in solution. The process could be extended to a broader range of microorganisms and metal oxides for the rational design of on-demand micro- and nanostructured metals. In addition, we show that the intrinsic composition of the biotemplates as well as their growth medium can introduce impurities that could potentially be used as dopants in the final silicon structures, and that could allow for tuning the composition of n-doped or p-doped biotemplated silicon for use as semiconducting building blocks.
sombre ainsi que la fabrication et la fonctionnalisation des chambres microfluidiques. Ce montage nous permettra de caractériser optiquement la pureté, la stabilité et la lon- gueur (distance interparticule) de nos dimères stabilisés par de courts oligomères d’éthy- lène glycol, vis-à-vis de la force ionique locale. Nous montrerons ainsi qu’entre des dimères ouverts et fermés, nous pouvons observer un décalage spectral allant jusqu’à 9,5 nm et une différence de distance interparticule atteignant 7,5 nm. Surtout, en calibrant quan- titativement les réponses optiques mesurées sur une caméra CCD couleur par rapport à des mesures sur un spectrographe à réseau, nous montrerons que le suivi spectral de la déformation nanométrique des dimères, et la différentiation entre boucles d’ADN ou- vertes et fermées, peuvent être effectués, en champ large, sur un détecteur à bas coût. Finalement, nous analyserons dans quelles conditions ces dimères autorisent la détection optique d’un ADN cible unique. Ces mesures nous indiqueront les limites actuelles de nos nanostructures en termes de réactivité et de stabilité.
Ce travail de thèse a porté sur l’étude de l’interaction entre une onde électromagnétique et des nano- structures plasmoniques complexes ou hybrides à différentes échelles d’espace et de temps.
D’un point de vue théorique, nous nous sommes intéressés à la réponse optique originale de nanostructures de métaux nobles caractérisée par des résonances plasmon de surface (RPS) liées à l’excitation collective des électrons de conduction. A travers différents exemples, nous avons montré que les interactions électroma- gnétiques entre nanostructures plasmoniques modifient la localisation et l’exaltation de l’intensité en champ proche optique et se traduisent par un décalage spectral des RPS. Nous avons alors calculé la densité volu- mique de charges et identifié les modes multipolaires excités dans ces nanostructures. Ensuite, nous avons utilisé les variations du champ électrique à proximité de nanostructures plasmoniques pour modifier la durée de vie, l’intensité de fluorescence ainsi que la statistique de photons de centres émetteurs. En particulier, nous avons montré que le temps moyen entre l’émission de deux photons consécutifs par un fluorophore pouvait être contrôlé en modifiant son environnement.
Nanostructured silver stands out among other plasmonic materials because its optical losses are the lowest of all metals. However, nano- structured silver rapidly degrades under ambient conditions, preventing its direct use in most plasmonic applications. Here, a facile and robust method for the preparation of highly stable nanostructured silver mor- phologies is introduced. 3D nanostructured gyroid networks are fabricated through electrodeposition into voided, self-assembled triblock terpolymer scaffolds. Exposure to an argon plasma degraded the polymer and stabi- lized the silver nanostructure for many weeks, even in high humidity and under high-dose UV irradiation. This stabilization protocol enables the robust manufacture of low-loss silver nanostructures for a wide range of plasmonic applications.