Silicon Solar Cells

The word out on solar energy is advancement, both in efficiency and flexibility. As with most areas of knowledge, solar progress must first occur on a basic level, starting with individual solar cells. One of the key defining factors in a solar cell is the type of semiconductor used to absorb sunlight and convert it into a useable electrical charge. While many new alternatives have been introduced to replace silicon, the earliest successful semiconductor in the solar cell, it is still the most widely used material in solar photovoltaic (PV) devices. Furthermore, the structure of silicon in the PV cell provides a basic guideline for other solar cell models.

Solar grade, or bulk silicon, has a crystalline structure. Each silicon atom consists of three layers filled with electrons that increase in number toward the center of the atom. As electrons in the outer shell are released, the inner electrons move to take their place, resulting in a locked structure. This is why most silicon solar cells are either N-type or P-type silicon cells. Through a doping process, N-type cells have been chemically altered to include phosporous, enabling more electrons to escape the outer shell of the atomic structure to become electricity. P-type silicon cells are doped with boron, which allows electrons to leave the atomic structure by creating positively charged holes in their place. The more free electrons roaming, the higher the electrical charge.

Bulk silicon can be found with multicrystalline, monocrystalline, or polycrystalline formations. Monocrystalline silicon consists of single-crystal wafer cells. They are characterized by high efficiency levels (around 15%), a more involved manufacturing process, and higher cost. Multicrystalline silicon is produced using multiple grains of molten silicon cast into ingots, which are cut into thin wafers and assembled into complete cells. Multicrystalline silicon is less efficient (around 12%) but cheaper to produce. It is more commonly manufactured. Polycrystalline silicon, a variation of multicrystalline silicon, also consists of multiple grade silicon and allows for more complex, high-speed electrical circuits.

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