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INNOVATIVE COMPONENTS OF SOLAR ENERGY

2012-02-27
Andrew (Gabriel) Livshits

Today, one of the most important areas of energy development - to provide electricity from solar panels

When the euphoria passes on the prospects of obtaining energy directly from the sun, begin to overcome the various technical and technological problems, only some of them, such as the pressing problems in the production of pure silicon and a noticeable loss of energy when it is received from the solar panels require an immediate solution

Recently, more research is conducted in the establishment of panels on the surface of the silicon coating

Dutch physicists have managed to create a silicon surface, which absorbs almost all visible light (but still significant part of the infrared spectrum), which falls on it.

The surfaces of this kind are known for a long time under the name "black silicon" - in this sense created by the Dutch silicon, of course, the blackest of them all.

For the first time the term "black silicon" originated in 1990, published in the journal Journal of Vacuum Science & Technology.

By studying the reactive ion etching of silicon surfaces, the researchers found an unexpected fact - the surface of a silicon substrate by etching without any mask (etching is usually used in lithography to produce the silicon surface of the right figure) is noticeably darkened.

After examining the surface with an electron microscope, the researchers found that in this case it does not change color in the banal, and the change in optical properties of the surface.

The reason for this change lies is this.

The essence of the method of reactive ion etching is that the substance of the substrate is removed by treatment of the ions towards the active substance (in the ions of bromine and chlorine).

The method is good, among other things, that allows you to choose the direction in which the removal of atoms from the substrate, however, the removal of the material is uneven.

Because of this, is formed on the substrate rather complex pattern of hollows and pillars formed by the reaction products of silicon ions.

Why exactly the relief that is formed, which is formed - not very clear, even now, after more than two decades after the discovery. Physicists say that it's just natural fluctuations of the ion flow and structure of the substrate, but a suitable model that could predict the resulting structure, they do not.

In addition, it is unclear why the thus treated silicon begins so well to absorb the light falling on it - it is assumed that the case of multiple reflection, refraction and dispersion of light.

Later, scientists were able to experimentally obtain a fairly regular structure, which are essentially the "forest" of the cones. Also from the 90s of last century, was discovered a few ways to get the black silicon.

For example, a silicon surface can be irradiated with laser pulses lasting a few femtoseconds (10-15 seconds), heat treatment and ultraviolet lithography.

The first was even patented by a group of Harvard, who organized the firm SIOnyx, in 2011, has received on the development of its technology from the U.S. Department of Defense $ 3 million.

In general, today the term "black silicon" refers to a class of silicon surfaces.
Black silicon interested scientists for many reasons. Let us consider the three main areas of application of this material.

First, black silicon can, in theory, noticeably increase the efficiency of solar cells.

The fact that the reflection of light silicon substrate battery - is, first and foremost, the loss of energy.

In turn, reducing the proportion of reflected light can increase the amount of energy produced by a battery. Now the batteries are used for different kinds of anti-glare coating, which, however, inferior to the black silicon.

Another area of application (in this direction works SIOnyx) is to create a more efficient compared to existing models, semiconductor detectors of electromagnetic radiation (and not necessarily in the visible range).

The development of this technology in the long term can result in improved performance of existing equipment without major changes in the production process.
Another, quite unexpected use black silicon found in the German physicists in 2008.

First, they prepared a plate of silicon covered with conical nano - needles height of 2 micrometers (needles were obtained using the same reactive ion etching).

It was found that irradiation of the plate with a laser beam on the one hand, the opposite side radiates in the terahertz range (the so-called T-rays).

The fact that T-rays can easily penetrate through the paper, clothing, cardboard, plastics and many other materials. They can be used to detect concealed weapons or explosives, diagnose tumors, searching for defects and cracks in materials.

The main obstacle, however, their widespread implementation is the lack of corresponding emitters. For example, the first source of coherent terahertz radiation (by abuse of language, such sources are called T-lasers) operating at room temperature, was established in 2008.

New work by the Dutch physicist black silicon is a logical extension of previous findings.
In 2011, they found that nanometer-scale metal cylinders on a silicon surface can absorb light quite well.

The effect was associated with plasmons - quasiparticles that represent the quantum fluctuations of the electron gas, in particular, in the metal.

In the new work, scientists have created a black silicon, which is a silicon surface, but with regularly spaced along it with silicon cylinders. For this surface was used already mentioned reactive ion etching.

Dimensions of the cylinder were 250 nanometers to 150 nanometers. Nano – forest was filled with a layer of silicon nitride Si3N4 thickness of 60 nm.

As it turned out, the material thus obtained reflects less than 2 percent of incident light in the visible range (small peak reflectivity was observed for wavelengths 650 nm) at an angle of incidence is not less than 60 degrees.

According to scientists, they have compared their black silicon obtained with the best anti-glare coating - at best the past reduced the proportion of reflected light up to 10 percent.

The high efficiency of absorption due to the fact that part of the radiation in the cylinders, "flowed" into the substrate. This is indicated by a computer model of black silicon, which was based on Mie scattering theory is modified (the original version - a scattering of a plane electromagnetic wave by a homogeneous sphere).

Notably, scientists have tried to take the place of the cylinder balls, but as it turned out, this battery is noticeably worse.

Scientists themselves are hoping that they have created technology will be used black silicon-on practice in the near future. However, if they can be the method used on an industrial scale is still unknown.

It seems to me, and multi-disciplinary group of professionals with whom our company works, there is a version of technology that can enable using the equivalent of the technical solutions developed in terms of formation of micro-relief on the surface of solar panels, a minimum reflection of the light flux

The following is a summary of the patent publication in the official USPTO data:

United States Patent Application 20120040166
Kind Code A1
Livschits; Gabreal; et al. February 16, 2012
________________________________________
Composite Material, Method of Manufacturing and Device for Moldable Calibration
Abstract
Composite materials and methods and systems for their manufacture are provided. According to one aspect, a composite material includes a collection of molded together multilayer capsules, each capsule originally formed of a core and shell. The shell, after a plastic deformation process, forms a pseudo-porous structure, with pores locations containing the capsule cores. The cores are made of a material, eg, synthetic diamond, which is harder than the external shell, which can be formed of, eg, a ductile metal such as copper. The composite material has high thermal and / or electrical conductivity and / or dissipation.
________________________________________
Inventors: Livschits; Gabreal; (San Francisco, CA); Flider; Gennadiy; (San Francisco, CA)
Serial No.: 108 597
Series Code: 13
Filed: May 16, 2011

In accordance with the basic features of the invention in order that would achieve almost total absence of reflection from the silicon panels, enough to create on the surface of the panels, at least a three-layer system of spherical geometry of nano-capsules, connected by a contact at one point and at least eight intersecting planes

First we need to disclose the construction of multi-level nano – capsules

The core of the capsule is a nano - aluminum sphere with a diameter of 10 nm
The sphere is covered with a shell of silicon thickness of 10 nm, thus the diameter of the nano - capsule is equal to 30 nanometers

When the vacuum coating of the nano - caps on the surface of the solar panels are in spherical capsules of a point contact with each other and the luminous flux is the area of contact with the surface of silicon by several orders of magnitude higher than that of conventional silicon-based coatings

In addition several layers of nano - capsules that are in point contact with each other create the best maze - a trap for the flux, which almost completely eliminates light reflected from the mirror surface coated with silicon

Cores of aluminum nano - capsules create a stable channel for reducing the electrical resistance in the way of current pulses to the systems of stabilization and transformation of the current pulses in a stable current with standard modes and parameters

Technologically, this solution is fully worked out and the possibility of mass production of solar cells is no doubt among experts

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