Slowing of carrier cooling in hot carrier solar cells

The concept of the hot carrier cell is to absorb a wide range of photon energies and, before the resultant "hot" carriers can thermalise with the lattice, separate and collect them in the external circuit. Carrier thermalisation typically occurs in a few picoseconds, hence a significant slowing of carrier cooling is required. This has only been observed at very high illumination intensities via a "phonon bottleneck" effect. The critical factor is the decay rate of these optical phonons into acoustic phonons, which occurs primarily via the Klemens mechanism. This paper discusses interruption of this mechanism in the wide "phononic band gap" of some binary compounds and modelling of a possible replication of this in quantum dot superlattices in which there is a modulation of the acoustic impedance.