Alternative Energy Devices (Solar Cells)

What happens when the world runs out of petroleum or fuels that are irreplaceable? A question of what alternative energy can then be used? Solar power seems to be an answer for the future as solar power is available in the day as long as the sun exists. Therefore, making solar cells an essential device to be discussed here.

Basically, a solar cell is a cell that converts light directly into electricity by the photovoltaic effect. I will explain the photovoltaic effect to explain things easier for the rest of the post. The photovoltaic effect is an effect which creates voltage of electricity in a material through exposure of electro-magnetic radiation.

Many currently available solar cells are configured as bulk materials that are subsequently cut into wafers and treated using "top-down" method of synthesis (silicon used as the most prevalent bulk material).All solar cells require a light absorbing material contained within the cell structure to absorb photons and generate electrons via the photovoltaic effect. The materials used in solar cells have properties that enables it to absorb wavelengths of solar light that reaches the earth surface. However, there other models of solar cells that are designed to absorb light even beyond Earth's atmosphere (outer space) as well. Light absorbing materials can often be used in different kinds of physical configurations to adapt to different light absorptions and charge separation mechanisms. Photovoltaic panels that are used for solar cells are generally made out of either silicon or thin-film cells.

Other materials that are configured as thin-films (e.g. inorganic layers, organic dyes, and organic polymers) that are deposited on supporting substrates but the third group are configured as nanocrystals used as quantum dots (electron-confined nanoparticles) embedded in a supporting matrix in a "bottom-up" approach. Silicon therefore still remains as the only material that is well-researched in both bulk (also called wafer-based) and thin-film configurations.

Materials discussed above does include materials for older generation solar cells to newer generation. Therefore, I will cover mainly on solar cells made of silicon. There are certainly plenty variation for silicon type solar cells but two common ones are amorphous silicon and crystalline silicon.

A silicon solar cell is produced namely from the element of pure silicon denoted with the symbol Si. Pure silicon element is taken from an impure variety and heated to the melting point of 1410 degrees Celsius. After reaching this melting point, the mass of impure silicon is cooled down and then separated from pure silicon. This separation can occur due to the fact that impurities of silicon have a slightly different melting point than pure silicon. This process is similar to the purification process of gold and other precious metals. The pure silicon from the separation process forms crystals as it cools. This crystal is then sliced into pieces resembling sausage which is further shaped into thin wafers. These wafers are then used for manufacturing circular silicon cells are usually about four inches in diameter.

Picture of a silicon made wafer

Next, the shaped silicon wafer is first "doped" (sprinkled) with an small amount of boron, to diversify the silicon wafer to another type of wafer called the P-type silicon layer while the opposite side of the wafer is doped further with phosphorus to form the N-type silicon layer. The only part of the cell that produces electricity is the wires that are connected to both the negative (N- type silicon) layer, and the positive (P-type silicon) layer that connects to either a battery or some other electronic component depending on location and environment.

General Mechanism of a solar cell






System of a solar cell

Crystals made by an element is nonetheless predictable because the same crystal will be produced every time. Crystalline solar cells are made from crystalline silicon and these cells are fragile as well as break and bend easily.

The breakdown of crystalline silicon in recent years has obviously became apparent science involving industry especially the Space Industry. Electricity producing modules that power space stations and satellites had must be replaced or else left as space waste. The amount of electric current that a crystalline silicon solar cell produces is larger than for amorphous silicon, but still only a small percentage of the total amount of the total sunlight that reaches Earth.

The crystalline structure of silicon can be seen in the following picture:

Now for how a solar cell works. An amorphous solar cell does not have the same definite structure that is predicted for crystalline silicon, and is therefore much more flexible. Usually amorphous cells can be found on handheld calculators or personal organizers. Unfortunately amorphous cells are not as efficient as crystalline cells, meaning the energy production with crystalline silicon is much higher. This kind of solar cell is used on boats, campers, and other modes of transportation because it is so flexible. Crystalline and amorphous silicon solar cells are not the only forms of solar cells available, but because other cells are not as efficient as silicon cells substitutes are not used.

A solar cell is actually a wafer of two layers. The top layer is P-Type Silicon, is the blue or purple part of the cell as seen in pictures, and has a positive charge. N-Type Silicon of negative charge occupies the lower layer and is usually not visible in pictures of solar cells. The process of adding elements to silicon is called doping. When Boron is added to silicon, P-Type Silicon forms. The addition of Phosphorus or Arsenic creates N-Type Silicon. The wafer formed by combining a level of P-Type and N-Type Silicon is displayed in the picture below. This wafer structure is called a PN Junction. Understanding the electron organization in these atoms illuminates the process of energy conversion in a solar cell.

This concludes how solar energy can be converted to electricity with ease with only simple materials found. Solar cells are devices that are certainly worthy developing.