Conversion of above- And below-bandgap photons via InAs quantum dot media embedded into GaAs solar cell

Quantum dots (QDs) provide photovoltaic conversion of below-bandgap photons due to multistep electron transitions. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons excited by high- energy photons. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AIGaAs atomically thin barriers) allow for suppression of photoelectron capture to QDs. To study these kinetic effects and to distinguish them from the absorption enhancement due to light scattering on QDs, we investigate long, 3-μn base GaAs devices with various InAs QD media with 20 and 40 QD layers. Quantum efficiency measurements show that, at least at low doping, the multi- step processes in QD media are strongly affected by the wetting layer (WL). The QD media with WLs provide substantial conversion of below-bandgap photons and for devices with 40 QD layers the short circuit current reaches 29.2mA/cnr. The QD media with band-engineered AIGaAs barriers and reduced wetting layers (RWL) enhance conversion of high-energy photons and decrease the relaxation (thermal) losses.