Urbach tail in intermediate band InAs/GaAs quantum dot solar cells

We demonstrate that the self-assembled InAs/GaAs quantum dots create perturbation to the GaAs lattice periodicity and form an extended Urbach tail, which provides additional energy states within the bandgap. From an external quantum efficiency measurement, we determine quantitatively the tailing distribution density of states near the band edge. We find that the Urbach tail is responsible for 45% of the total enhanced photocurrent below the gap and leads to a degradation of the open-circuit voltage and an increase of the short-circuit current.