A thin-film solar cell is a second generation solar cell that is made by depositing one or more thin layers, or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies, including cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon (a-Si, TF-Si).
A Plasmonic solar cell is a type of thin film solar cell that converts light into electricity with the assistance of plasmons. They are typically less than 2 μm thick and theoretically could be as thin as 100 nm. They can use substrates which are cheaper than silicon, such as glass, plastic or steel. One of the challenges for thin film solar cells is that they do not absorb as much light as thicker solar cells made with materials with the same absorption coefficient. Methods for light trapping are important for thin film solar cells. Plasmonic cells improve absorption by scattering light using metal nano-particles excited at their surface plasmon resonance. This allows light to be absorbed more directly without the relatively thick absorber layer required in other types of thin-film solar cells. However, this type of solar cell also normally demands a thin transparent conducting oxide (TCO) to function for realistic photovoltaic absorber thicknesses and only recently have methods been advanced that allow high conductivity while maintaining high optical transmission of the TCO. There is still considerable research necessary to enable the technology to reach its full potential and commercialization of plasmonic enhanced solar cells.
Nanocrystal solar cells are solar cells based on a substrate with a coating of nanocrystals. The nanocrystals are typically based on silicon, CdTe or CIGS and the substrates are generally silicon or various organic conductors. Quantum dot solar cells are a variant of this approach, but take advantage of quantum mechanical effects to extract further performance. Dye-sensitized solar cells are another related approach, but in this case the nano-structuring is part of the substrate.
There are currently many research groups active in the field of photovoltaics in universities and research institutions around the world. This research can be categorized into three areas:
making current technology solar cells cheaper and/or more efficient to effectively compete with other energy sources;
developing new technologies based on new solar cell architectural designs;
and developing new materials to serve as more efficient energy converters from light energy into electric current or light absorbers and charge carriers.
Nanostructured materials are being investigated and developed as versatile components of optoelectronic devices with the ability to manipulate light (via plasmonic enhancement, photonic crystals, and so on) and control energy flow at nearly the atomic level. Nanostructured solar cells — a type of third- or next-generation solar cell1 — include those that are based on nanostructures and/or nanostructured interfaces such as nanowire, mesoscopic and quantum dot solar cells. They hold great promise towards new approaches for converting solar energy into either electricity (in photovoltaic devices) or chemical fuels. There are challenges to overcome but the potential benefits are worth the efforts.
A quantum dot solar cell is a solar cell design that uses quantum dots as the absorbing photovoltaic material. It attempts to replace bulk materials such as silicon, copper indium gallium selenide (CIGS) or CdTe. Quantum dots have bandgaps that are tunable across a wide range of energy levels by changing the dots' size. In bulk materials the bandgap is fixed by the choice of material(s). This property makes quantum dots attractive for multi-junction solar cells, where a variety of materials are used to improve efficiency by harvesting multiple portions of the solar spectrum.
A perovskite solar cell is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer. Perovskite materials such as methylammonium lead halides are cheap to produce and simple to manufacture.
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