Efficient Schottky-quantum-dot photovoltaics: The roles of depletion, drift, and diffusion

PbS colloidal quantum dot photovoltaic devices in a Schottky architecture have demonstrated an infrared power conversion efficiency of 4.2%. Here, we elucidate the internal mechanisms leading to this efficiency. At relevant intensities, the drift length is 10 mu m for holes and 1 mu m for electrons. Transport within the 150 nm wide depletion region is therefore highly efficient. The electron diffusion length of 0.1 mu m is comparable to neutral region width. We quantitatively account for the observed 37% external quantum efficiency, showing that it results from the large depletion width and long carrier lifetime combined. (c) 2008 American Institute of Physics.