Absorption Characteristics of Quantum Dot Array Based Intermediate Band Solar Cell

Intermediate band solar cells (IBSC) have emerged as an alternative design for solar cells that can dramatically increase power conversion efficiency. It is demonstrated here that a k·p multiband theory with periodic boundary conditions can be applied to predict the electronic structure and absorption characteristics of semiconductor QD arrays. Such arrays produce a mini-band (IB) located in the forbidden energy gap of the barrier material that is well separated from its valence and conduction bands. Analysis of the electronic and absorption structure suggest that the most promising design for an IB solar cell material, that will exhibit its own quasi-Fermi level, is to employ small QDs (~6-10 nm QD lateral size) arranged in a periodic array. Use of larger (> 20 nm QD lateral size) QDs leads to extension of the absorption spectra into a longer wavelength region but does not provide a separate IB in the forbidden energy gap.