Thin-film Solar Cells shall Give a Boost To Your Business

Today power is a big requirement in every field of life , especially when you are a business person and you need it for the production or other purposes. The solar panel is an enduring icon of the quest for renewable energy. You'll see the black-paned rectangles on the rooftops of houses or assembled into arrays across fields and prairies. But the panel as we have come to know it -- 5.5 feet by 2.75 feet by 2 inches (1.7 m by 0.8 m by 5 cm) -- may be history. That's because a new type of technology stands ready to take its rightful place next to traditional silicon wafer-based panels as an efficient, cost-effective way to convert sunlight into electricity.

Beyond 2010, production capacity will increase even more as thin-film PV cells find their way into solar-powered commercial buildings and homes, from California to Kenya to China.

Other than their flexibility, how do thin-film solar cells compare to traditional solar cells? Why are they more cost efficient? And are they the kind of energy source that will make solar power a truly viable alternative to coal and nuclear power?

What is a Thin-film Solar Cell?

If you've used a solar-powered calculator, you've seen a solar cell based on thin-film technology. Clearly, the small cell in a calculator is not big and bulky. Most are about an inch (2.5 cm) long, a quarter-inch (0.6 cm) wide and wafer-thin. The thinness of the cell is the defining characteristic of the technology. Unlike silicon-wafer cells, which have light-absorbing layers that are traditionally 350 microns thick, thin-film solar cells have light-absorbing layers that are just one micron thick. A micron, for reference, is one-millionth of a meter (1/1,000,000 m or 1 µm).

Thin-film solar cell manufacturers begin building their solar cells by depositing several layers of a light-absorbing material, a semiconductor onto a substrate -- coated glass, metal or plastic. The materials used as semiconductors don't have to be thick because they absorb energy from the sun very efficiently. As a result, thin-film solar cells are lightweight, durable and easy to use.

There are three main types of thin-film solar cells, depending on the type of semiconductor used: amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium gallium deselenide (CIGS). Amorphous silicon is basically a trimmed-down version of the traditional silicon-wafer cell. As such, a-Si is well understood and is commonly used in solar-powered electronics. It does, however, have some drawbacks.

One of the biggest problems with a-Si solar cells is the material used for its semiconductor. Silicon is not always easy to find on the market, where demand often exceeds supply. But the a-Si cells themselves are not particularly efficient. They suffer significant degradation in power output when they're exposed to the sun. Thinner a-Si cells overcome this problem, but thinner layers also absorb sunlight less efficiently. Taken together, these qualities make a-Si cells great for smaller-scale applications, such as calculators, but less than ideal for larger-scale applications, such as solar-powered buildings.

Promising advances in non-silicon thin-film PV technologies are beginning to overcome the issues associated with amorphous silicon.

Structure of Thin-film Solar Cells

Because structure and function are so closely linked with solar cells, let's take a moment to review how they work. The basic science behind thin-film solar cells is the same as traditional silicon-wafer cells.

Photovoltaic cells rely on substances known as semiconductors. Semiconductors are insulators in their pure form, but are able to conduct electricity when heated or combined with other materials. A semiconductor mixed, or "doped," with phosphorous develops an excess of free electrons. This is known as an n-type semiconductor. A semiconductor doped with other materials, such as boron, develops an excess of "holes," spaces that accept electrons. This is known as a p-type semiconductor.

A PV cell joins n-type and p-type materials, with a layer in between known as a junction. Even in the absence of light, a small number of electrons move across the junction from the n-type to the p-type semiconductor, producing a small voltage. In the presence of light, photons dislodge a large number of electrons, which flow across the junction to create a current. This current can be used to power electrical devices, from light bulbs to cell phone chargers.

Traditional solar cells use silicon in the n-type and p-type layers. The newest generation of thin-film solar cells uses thin layers of either cadmium telluride (CdTe) or copper indium gallium deselenide (CIGS) instead. One company, Nanosolar, based in San Jose, Calif., has developed a way to make the CIGS material as an ink containing nanoparticles. A nanoparticle is a particle with at least one dimension less than 100 nanometers (one-billionth of a meter, or 1/1,000,000,000 m). Existing as nanoparticles, the four elements self-assemble in a uniform distribution, ensuring that the atomic ratio of the elements is always correct.

The layers that make up the two non-silicon thin film solar cells are shown below. Notice that there are two basic configurations of the CIGS solar cell. The CIGS-on-glass cell requires a layer of molybdenum to create an effective electrode. This extra layer isn't necessary in the CIGS-on-foil cell because the metal foil acts as the electrode. A layer of zinc oxide (ZnO) plays the role of the other electrode in the CIGS cell. Sandwiched in between are two more layers -- the semiconductor material and cadmium sulfide (CdS). These two layers act as the n-type and p-type materials, which are necessary to create a current of electrons.

If with the help of this our power crises can be resolved then you may have a boost to your business.