In this thesis, five intrinsic loss mechanisms which fundamentally limit solar
energy conversion efficiency are identified. The three dominant mechanisms are
thermalisation loss, below Eg loss and Boltzmann loss. Targeting these three losses
through alternative device design is the only way substantial efficiency enhancement
might be achieved. The hot carrier solar cell targets these dominant mechanisms
and hence has a theoretical limiting efficiency, under maximum solar concentration,
in excess of 80%. Despite clear efficiency advantages, a hot carrier solar cell has
never been experimentally demonstrated because two key development challenges
remain: energy selective contacts and absorber materials which maintain a hot
carrier distribution under realistic levels of incident solar irradiation.
In this study, strain-balanced InGaAs/GaAsP QW structures with a range of QW
parameters were characterised spectroscopically in order to determine the suitability
of this material system as a hot carrier absorber. In a deep, wide well sample, a
temperature gradient between the carrier distribution and the surrounding lattice
of 150 K was demonstrated using continuous wave photoluminescence spectroscopy.
This technique was also used to calculate a thermalisation coefficient for each
sample, allowing for comparison with other hot carrier studies.
Time resolved photoluminescence measurements were used to identify cooling
pathways occurring in this material system. Bi-exponential cooling behaviour was
observed, indicating that two different mechanisms with different characteristic
cooling lifetimes were dominating carrier cooling. In the deep, wide well sample it
was determined that peak LO phonon distribution temperatures of at least 500 K
above that of the surrounding lattice would be required to produce the observed
carrier cooling.