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 (V-oc) 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 V-oc.