Photovoltaics (PVs) known as solar cells are considered as one of the most significant means of tapping solar energy. PV cells are devices that trap solar energy to convert it into electricity. They are made from semiconducting material such as silicon and gallium. A PV cell mainly has two functions namely, photogeneration of charge carriers in a light absorbing material and separation of charge carriers to a conductive contact that converts it into electricity. Recently, researchers have shown that apart from solar energy, other forms of heat can be used to generate electricity. This new generation of photovoltaic cells is called thermophotovoltaics. It is a highly efficient and reliable system that can use concentrated sun light, nuclear power, fossil fuel, or a radioisotope heat source to heat an intermediate thermal emitter due to which the emitter emits electromagnetic radiation that eventually illuminates the photo cells which in turn converts the incident radiation/light to electricity.
Using this principle, researchers from the Massachusetts Institute of Technology (MIT) have developed a new button-sized thermophotovoltaic system that could potentially replace rechargeable lithium-ion batteries used in consumer electronic devices such as laptops and cell phones. The newly developed button-sized micro power generators use butane as the fuel input, and have silicon-based microreactors as the central system of the micro power generator. Cylindrical tube inlets supplies butane fuel and oxygen to the microreactor containing photonic crystals on the surface of the reactors. The microreactor converts the fuel inputs to heat and the waste is discarded through another external outlet tube. In order to increase the efficiency of converting light to electricity compared to previous systems, the researchers etched the surface of the photonic crystals to create billions of tiny pits, giving the photonic crystals an ability to emit light at wavelengths matching those wavelengths of light at which the photovoltaic cells are at their best in converting the incident light to electricity. The photonic crystals were made out of tungsten, as this material was identified to give the best results on matching wavelengths. The photovoltaic cells were mounted against the face of the microreactors with a tiny gap so as to facilitate this conversion of light to electricity.
The research team led by Marin Soljacic, professor of physics at MIT, used the silicon microreactor created by Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering, at the Microsystems Technology Laboratories of MIT and borrowed the idea of engineering nanoscale pits to emit a completely different spectrum of light from a research by John D. Joannopoulos, the Francis Wright Davis Professor of Physics at MIT and others. According to MIT researchers, the principle of using nanoscale pits has been successfully used to create more efficient light-emitting diodes, lasers, and optical fibers. According to the creators of the photovoltaic conversion system, this new micropower generator system could be highly beneficial for powering portable power electronics as butane can run three times longer than a traditional lithium-ion battery of same size and weight. Also, the new system can be refueled instantly by simply replacing the cartridge containing a fresh supply of butane. However, the photovoltaic system is still in research stage and the MIT researchers are now seeking partners and collaborating with other researchers to create new electricity generating devices. Even though in its nascent stage with no set commercialization date, MIT researchers have shown that this new research initiative can potentially have a huge implication on the multibillion dollar power supply market for consumer electronic devices. The immediate application of this could be in the military for powering soldier’s gadgets, which require batteries that last longer and can be recharged instantly.
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