Intraband absorption for normal illumination in quantum dot intermediate band solar cells

In the current intermediate band solar cells made with InAs quantum dots (QDs) in GaAs, the transitions by absorption of photons between the intermediate band and the conduction band for illumination normal to the cell surface is very weak or, more often, undetectable. We model the QD as a parallelepiped potential well and calculate the envelope function of the electron wavefunctions. By obtaining the dipolar matrix elements we find that, with the present shapes, this absorption is forbidden or very weak. Deeper QDs with smaller base dimensions should be made to permit this absorption.