Indium gallium nitride (InGaN)-based semiconductors have large bandgaps, which has allowed the creation of ultraviolet and bright blue-emitting LEDs and lasers. However, a large bandgap can be a plus for use in detectors and solar cells as well, because they have a high response to short-wavelength light (down to 370 nm). Researchers at the University of California–Santa Barbara and the École Polytechnique (Palaiseau, France) have demonstrated InGaN/GaN solar cells that have an internal quantum efficiency as high as 97% and a peak external quantum efficiency (EQE) of 72%—the latter achieved by inducing a 41 nm (root mean square) surface roughness during fabrication.
The cells, which were fabricated by metal-organic chemical vapor deposition on sapphire substrates, have an InGaN/GaN thickness of 360 nm. A palladium/gold grid collects the current; the open-circuit voltage is 1.89 V. Despite the high EQE, at least 20% of the incoming light is either reflected or transmitted through the cell, and thus there is room for further improvement in efficiency. This type of short-wavelength photovoltaic cell has potential as one component in very high-efficiency multijunction solar cells, where it would convert the highest-energy portion of the solar spectrum. Contact Elison Matioli at [email protected].