Phononic modelling of nanostructures for the hot carrier solar cell

Abstract

Computational modelling of atomic vibrations of nanostructures, such as quantum dot superlattices, has been performed with respect to the Hot Carrier Solar Cell (HCSC). The goal of this modelling is to find systems that have large phononic bandgaps. These systems are expected to have decreased phonon decay and thus increased hot carrier lifetimes. These long hot carrier lifetimes are central to the operation of the hot carrier solar cell. Phonon dispersions and densities of states (DOS) have been computed in the harmonic approximation for a variety of quantum dot (QD) superlattice (SL) geometries. A positive result for phonon bandgaps that inhibit first order phonon decay from the harmonic approximation modelling is achieved for a large number of symmetrically placed and relatively light elements in an otherwise heavy matrix. This arrangement produces high energy split off bands well above the rest of the phonon bands. Large mass differences between the atoms are required. This circumstance arises for highly constrained FCC QD superlattices and core-shell geometries with very thin shell layers. Indications for other realistic possibilities for phonon systems are also shown, such as B:In and SK growth InAs:InGaAlAs QD structures of reduced size. Steps were taken towards producing phonon dispersions for realistic systems involving lattice mismatch, interface dipoles and QD SL disorder. Time dependent modelling of superlattices has been performed. Electronic structure calculations to produce surface potentials and to increase the speed of interface structural optimizations have also been performed.