Fundamental limitations of hot-carrier solar cells

Abstract

Sunlight-generated hot-carrier transport in strongly absorbing direct band-gap GaAs---among the most optimal of semiconductors for high-efficiency solar cells---is simulated with an accurate full-band structure self-consistent Monte Carlo method, including short- and long-range Coulomb interaction, impact ionization, and optical and acoustic phonon scattering. We consider an ultrapure 100-nm-thick intrinsic GaAs absorber layer designed with quasiballistic carrier transport that achieves complete photon absorption down to the band edge by application of careful light trapping and that has a generous hot-carrier retention time of 10 ps prior to the onset of carrier relaxation. We find that hot-carrier solar cells can be severely limited in performance due to the substantially reduced current density caused by insufficient extraction of the widely distributed hot electrons (holes) through the requisite energy selective contacts.