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 of electrons to the conduction band continuum resulting in an overall faster carrier collection. Using Ie V 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 (1 0-12s) from deep quantum wells rather than several ns, as it is the case for conventional designs. A preliminary evaluation of a GaAs/GaAsN multi-quantum well 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. The approach demonstrated here can be readily extended to other material systems and photovoltaic devices leading to significant efficiency improvements well beyond what seems achievable with conventional single junction counterparts.