Theoretical model of quantum dot array based intermediate band solar cell: Effect of Sb induced type II alignment on dynamical processes

Abstract

We present a theoretical model for the design and analysis of semiconductor quantum dot array based intermediateband solar cells. Information on the electronic structure and wave functions are used to estimate the most relevant radiative as well as non-radiative (Auger effect related) times between the intermediate (IB), conduction (CB) and valence (VB) bands. Analysis of dynamical processes in GaAs/InAs QD array reveal that: (i) the radiative transition time between CB→IB is at least one order of magnitude longer than the radiative time between IB→VB, and (ii) the most detrimental non-radiative time that might prevent quasi-Fermi level separation between CB and IB upon external illumination, required for proper IBSC operation, is Auger electron cooling. It is ∼3 orders of magnitude faster than any other scattering time and is in the ps time domain. In order to improve the dynamical conditions for possible formation of quasi-Fermi level separation between the CB and IB, we employ methods of quantum engineering to design the type II alignment, using a GaAsSb barrier buffer. By changing the Sb amount in the buffer region, we predict an increase of the IB→VB radiative time to the same time scale as CB→IB radiative time with simultaneous increase of the Auger electron cooling to ∼ 0.1 ns.