Harvesting Solar Power with Nanomaterials

Solar power is the most abundant renewable energy source for human beings. Sun provides the earth with energy that is 10,000 times more than the energy needed for human applications. The main issue is the ability to harvest this energy, and the ability to adjust this huge amount of available energy into a sustainable long term energy source. Solar energy can be converted into electrical energy by photovoltaic (PV) technology. PV is the conversion of light into electrical current in which PV solar cells are used. In our previous blog, namely Nanotechnology and Energy, we mentioned how nanomaterials show favorable applications in solar energy harvesting. Here we investigate which nanomaterials can be used and what are the properties that make these nanomaterials highly applicable in solar technology.

In PV solar cells, electricity is produced in three steps; firstly, light is absorbed by the material used, after that charge separation takes its place in the cells layer, and finally energy is extracted in the form of electricity by the outer circuit. PV solar cells that are currently used in markets are mostly silicon based solar cells. Silicon is a semi-conductor which can be prepared as p-type and n-type. P-type silicon has positive charges (holes) while n-type has negative charges (electrons). When light is absorbed it causes the electrons to transfer from n-type layer to p-type layer which causes charge separation between these two type layers which can be extracted as electric current.

Currently, PV market is based on silicon wafer solar cells. Silicon wafers are made of crystalline silicon and their thickness is around 100-300 mm. Silicon wafer based solar cells consists ofsingle crystal and polycrystalline silicon. Silicon wafer based solar cells have efficiencies in the range of 15% to 25%. The efficiency limitations arise from the large energy band gap, charge recombination,optical andresistive losses. The introduction of nanomaterials into the PV solar cells can provide big improvement by controlling the band gaps of semiconducting materials, improving the optical and conducting properties, and solving charge recombination problems. Moreover, it can have huge effects on the cost of the solar technology.

Nanomaterial solar cells are classified as the second generation of solar cells. Thin film layers (1–2 nm), quantum dots, polymeric and nanophase material solar cells are some examples of the new nanomaterial based solar cells. Thin film layer solar cells can be made of thin film silicon, cadmium telluride, copper indium gallium selenide, quantum dots, dye-sensitized and other organic materials. These thin films decrease the total cost of the solar technology because lesser material is used in the production of these cells. Nanostructured layers in thin film solar cells have important advantages over the silicon wafer layers due to the ability of small size manipulation. In nanostructured layers, charges travel over shorter path and recombination losses are greatly reduced. Moreover, the energy band gap of various layers can be designed by varying the size of nanoparticles. These important properties of nanostructured layers and quantum dots make them favorable options for solar cell technology.

The application of other nanomaterials such as graphene and carbon nanotubes is investigated to achieve higher efficiencies in solar cells. Research works have been made to develop graphene sheets with other nanoparticles that could produce up to 1000 times much power than conventional solar cells for a given amount of material. This could be achieved by producing solar cells with one atom thick graphene sheets. Other research works are done to make solar cells out of carbon nanotubes and buckyballs which have high conducting and absorption properties. Using carbon nanotubes with other quantum dots and polymers increase the conversion efficiency of the solar cell. Another type of solar cells can be installed as a coating on windows or other building materials are referred to as Building Integrated Photovoltaics. These solar cells can change the way of extracting the solar energy in our life. In the following articles we will explore more future applications of nanomaterials that are used in harvesting the solar power.

Posted by Mohammed Zabara

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