Theory of Quantum Dot Arrays for Solar Cell Devices

Abstract

Vertically or laterally coupled semiconductor quantum dot (QD) arrays emerged recently as promising structures for the next generation of high-efficiency intermediate band solar cell (IBSC), due to their ability to facilitate the formation of mini-bands. The quantum coupling effect, that exists between states in QDs of an array, influences the electronic and optical properties of such structures. We present here a method based on multi-band k Á p Hamiltonian combined with periodic boundary conditions, applied to predict the electronic and optical properties of InAs/GaAs QDs based vertical and lateral QD arrays. Formation of the intermediate band (IB) in all cases was achieved via delocalisation of the electron ground state (e0). By changing the geometry of the QD arrangement in arrays we have identified conditions for the IB to be separated by a pure zero density of states from the rest of states in the conduction band (CB). Due to symmetry of the QD array lattice and QD states itself, which are C 2v for the zinc blende QDs, the electronic and absorption structure needs to be obtained via sampling throughout the reciprocal space in the first Brillouin zone of QD arrays. 5.1 Introduction The intermediate-band solar cell (IBSC) [1] is one of the promising candidates for next generation solar cells (SC) with an estimated detailed balance efficiency of 63.8 % under idealized conditions and maximum concentration [2]. The interme-diate band (IB) material is characterised by the existence of an electronic energy band of allowed states within the conventional-energy band gap, E g (CB,VB), of the host material, splitting it into two subgaps, E g (CB,IB) and E g (IB,VB). This band