Modified Shockley-Queisser limit for quantum dot solar cells

We discuss the fundamental limits affecting the conversion efficiency of quantum dot solar cells. We demonstrate using a modified detailed balance analysis that the existence of an extended tailing density of states fundamentally enhance the dark saturation current density and lead to a degradation of the open circuit voltage. We predict how the open circuit voltage (Voc) changes with the tail width and find agreement with the general trend observed experimentally. In practice, the existence of non-radiative recombination would further reduce Voc.