Resonant thermo-tunneling design for ultra-efficient nanostructured solar cells

Nanostructured solar cells are touted to lead to super high photo-conversion efficiencies. Nevertheless the inclusion of potential energy fluctuations associated with those structures hinders the smooth vertical transport of photo-generated carriers. We present an innovative energy level engineering design that significantly facilitates the collection of all photo-generated carriers. Using dilute nitride III-V semiconductor quantum wells embedded in a conventional III-V GaAs host, we demonstrate the possibility of achieving a quasi-flat valence band that will ease the smooth transport of holes. The conduction band confinement energies are designed in a way that promotes thermo-tunneling electrons from their potential wells to the conduction band continuum. Energy levels were calculated by including strain and spin-orbit interaction. The calculation of confinement energies was also undertaken. Once confinement energies and potential barrier heights were determined we complemented the theoretical evaluation by calculating carrier escape times via thermionic and tunneling routes at 300 K. Here we demonstrate that an optimized resonant thermo-tunneling design leads to ultra rapid escape. The suggested approach is thus expected to circumvent recombination losses and lead to a substantial carrier collection and efficiency improvements.