Slowed hot carrier cooling in Multiple Quantum Wells for application to Hot Carrier Solar Cells

The Hot Carrier solar cell has the potential to yield a very high efficiency, well over 50% under 1 sun. Multiple quantum wells have been shown to have significantly slower hot carrier cooling rates than bulk material [1,2] and are thus a promising candidate for hot carrier solar cell absorbers. However, the mechanism(s) by which hot carrier cooling is restricted is not clear. Presented is a systematic study of carrier cooling rates in GaAs/AlAs MQW with either varying barrier or varying well thickness. These allow a determination as to whether the mechanisms of either a reduction in hot carrier diffusion; a localisation of phonons emitted by hot carriers; or mini-gaps in the MQW phonon dispersion are responsible for reduced carrier cooling rates. Initial devices fabricated using MQW as hot carrier absorbers indicate promising photovoltaic performance which result from collection of hot carriers.