# Scattering Problem in Solar Energy, Solved by Nanotechnology in Lumerical

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Solar power is the most abundant source of energy on earth. There’s enough solar energy hitting the Earth every hour to meet all of humanity’s power needs for an entire year. Every ounce of oil, every lump of coal, and every cubic foot of natural gas could be left in the ground if only we could capture one hour’s worth of solar energy each year. That’s the scale of the opportunity. To put the it into a different perspective, if we covered the Mojave Desert with solar arrays, it would generate more than twice as much electricity as the U.S. uses annually.

Diving deeper into the realm of solar energy, it is impossible not to stumble upon nanotechnology. Nanotechnology has been a massive step to increasing solar cell efficency, design, manufacture, and decreasing cost. To throughly understand how nanotechnolgy plays a key part of photovolatic technology, I decided to model it on Lumerical. This model in paticular, is solving a scattering problem. Before jumping into the simulation, here is a basic review of what solar cells, nanotechnology and plasmonic simulations are.

# Solar Cells

Often reflered to as photovoltaic cells (PV), solar cells are a key part of solar panels and solar energy as a whole. A solar cell is an electrical device that can directly conver solar energy (the energy of light) into electricty through the photovoltaic effect. A common solar cell can produce a maximum of 0.5 volts. A single AA battery produces 1.5 volts in its entire lifetime, while a solar cell produces 1/3 of that. There are a total of 32 solar cells in a solar panel.

As you can see from the diagram above, the solar panel is made up of two layers of silicon. These layers of silicon are treated to let electricity flow through them when they are expose to sunlight. The top layer is negativtly charge while the bottom is positively charged with a thin junction inbetween the two layers. As the sunlight (photons) hit the layers of silicon, elextrons pass through the thin junction, creating electrical current that is then funneled out into a seperate souce.

However, if you look back up, I mentioned that each solar cell only produces 0.5 volts, and each solar panel produces a total of 16 volts. By common sense, you can probably deduct that the sun produces more than 16 volts of energy, even on a cloudy day. The sun produces 3.86 x 10²⁶ watts of energy at any moment of time. Most of that however goes into space, but 1.74 x 10¹⁷ hit the earth; at any given moment. SO how is it that we can only produce 16 volts of energy from that? Is our process to convert energy that innefficent? Is our technology that behind? Is a varierty of reasons that mainly portain to our technology being old and outdated?

Yes. Yes to all of those questions. While we havent made large strides in advancing solar energy we still are not able to maximize solar panels so that they can capture a larger portion of the suns energy, convert it into raw energy, and then use that to power the world. However scientists have found that using nanotechnology has increase their efficeny rate by almost 15–20%!

# Nanotechnology

Nanotechnology is the manipulation of matter on an atomic scale. Nanotechnology is often used to produce new and different types of structures, materials and devices like solar panels. As I previously mentioned, nanotechnology is mainly used to help with the design and manufacturing of thin-film PV cells.

The diagram above shows the schematics of a PV (photovoltaic) cell. Nanomaterials have the potenitial to enhace the preformance of each layer in the cell; from more transparent coatings and more conductive electrodes to more efficent absorbers. The sun first hits the electron hole pair, the part that is postively and negatively charged. To get to the electron hole pair, it has to go through an antireflection coating, grid contract, transparent conducting oxide, junction former, absorber, and finally the rear contact where the electron hole-pair is located. The external load keeps these layers together and helps it appear more cohesive.

Nanostructures can also allow efficient solar cells to be made from cheaper, more conventional materials, like silicon and titanium dioxide. Although there will be cost barriers involved in developing mass-production techniques for nano-enhanced PV cells, the use of cheaper raw materials will allow the cost of commercial solar cells to continue to decrease.

# Plasmonic Simulations

Before jumping into what plasmonic simulations are, its important to understand what a plamonic mode is. A plamonic mode is when nanostructures made of metals such as gold and silver are illuminated with visible light, plasmonic modes can be excited that cause conduction electrons to oscillate. Plasmons in nanotechnology are the oscillations of free electrons that are the consequence of the formation of a dipole in the material due to electromagnetic waves. Nanoplasmonics is the study of optical phenomena in the nanoscale vicinity of metal surfaces.

I orginally started with a scattering problem. As you can see with the image below, a scattering problem in solar energy is when the sun is shining on an object (like a solar panel), but due to its structure, itscatters the light into its scattered field, with a minimum amount going to its reciver. I have modeled a simulation on FDTD in Lumerical that helps control the light to one reciever.

First, I had to set the simulation parameters. These changes surrounded 2D/3D, the simulation time, temperature, material type, boundaries, etc. For a scattering problem in paticular, I found it helpful to use PML for all of the boundaries. Some of the smaller setting changes that I found helpful included changing it to nanometers (regarding the size of the simulation), creating a 3D simulation (instead of pure 2D), making the simulation time 1000 femtoseconds, and enabling a simulation domain of 200X3. I tried messing around with the mesh settings, but I found the simulation ran 10x smoother when I left them alone!

Below, you can see what my screen looked like before and after these changes.

Before running the simulation, I had to add a source. For a scattering problem, we want to us a plane wave source. If you have PMLs in all directions (which we do), you need to use a total field/scattered field. If you have periodic simulations however, you need to use a plane wave source. If you are using waveguides, you want to use a mode source. Below, you can see what its like before, during, and after you edit the geometry.

This is what it looks like when you press play on the simulation. It lasts for about 8 seconds, and looks like a short pulse. The color inside the box is called the total field range. On the outside, you can see that there is no electric fireld becuase thats where the scattering field stops. The pod signifies the PMS border.

Lets take this one step further. What if we were able to add a structure in the middle of the PMS field? How would that affect the scatter range? Could we use that object to direct mroe light into the reciever?

To test this theory, lets add a particale. You can choose any shape that you want, although I chose a sphere. You can see the differnet angles of the box when you see the sphere from the picture below.