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 10μm for holes and 1μm for electrons. Transport within the 150nm wide depletion region is therefore highly efficient. The electron diffusion length of 0.1μm 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.