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

We present a theoretical model for the design and analysis of semiconductor quantum dot array based intermediate-band 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.