Resonant thermo-tunneling design for high performance single junction quantum well solar cells

Abstract

In a material system displaying a negligible valence band offset, which enables the smooth transport of holes, we show that the conduction band confinement energies and barrier thicknesses can be designed to favor a sequential thermionic promotion and resonant tunneling to adjacent wells resulting in overall faster carrier collection. Using 1eV dilute nitride semiconductor quantum wells embedded in conventional GaAs solar cells, we present practical energy level engineering designs that significantly facilitate the collection of all photo-generated carriers within several ps (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> s) rather than several ns as it is the case for conventional deep multi-quantum well designs. A preliminary evaluation of a GaAs device incorporating such thermo tunneling design indicates potential for significant efficiency improvement over a conventional GaAs solar cell, thus surpassing the Shockley-Queisser efficiency limit for a single junction device.