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

In a material system displaying a negligible valence band offset, which enables the smooth transport of holes, we show that the conduction band (CB) confinement energies and barrier thicknesses can be designed to favor a sequential thermionic promotion and resonant tunneling of electrons to the CB continuum resulting in an overall faster carrier collection. Using 1 eV dilute nitride semiconductor quantum wells that are embedded in conventional GaAs solar cells, we present practical energy-level engineering designs that significantly facilitate the collection of all photogenerated carriers within several picoseconds (10
$^{-12}$
 s) from deep quantum wells rather than several nanoseconds, as it is the case for conventional designs. A preliminary evaluation of a GaAs/GaAsN multiquantum well device that incorporates such thermotunneling 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.