Intermediate Band Photovoltaics

Intermediate band photovoltaics is a solar cell design intended to exceed the Shockley-Queisser limit on conventional single junction solar cell efficiency by introducing an extra energy level, the intermediate band, between a semiconductor own valence and conduction bands. The intermediate band lets two photons that each carry less energy than the material bandgap combine to excite an electron all the way from the valence band to the conduction band, increasing the photocurrent the cell can generate. The approach is theoretically promising: a cell with a single intermediate band has a calculated maximum efficiency of 63.2 percent under concentrated sunlight, or 47 percent under ordinary sunlight, and a cell with multiple intermediate bands has a theoretical ceiling of 77.2 percent. In practice three fabrication approaches are being explored, quantum dot structures, which have reached about 18.3 percent efficiency experimentally, highly mismatched alloys, under one percent so far, and bulk materials with deep level impurities, with increased non radiative recombination and difficulty controlling carriers within the intermediate band remaining the chief obstacles to a practical device. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/