Observation of bimolecular carrier recombination dynamics in close-packed films of colloidal CdSe nanocrystals

We study the intensity dependence of the photoconductivity in close-packed films of CdSe quantum dots in which the photoconductivity is characterized by a low density of trapped charges. We find that the intensity dependence of the photocurrent is nonlinear, which is indicative of bimolecular charge carrier recombination dynamics. We present a physical model for the intensity dependence of the photocurrent that is used to fit the data and extract a ratio of the density of carriers to the density of trapped charges. As our model predicts, we show that the current vs intensity plot becomes more linear when the carrier density is decreased.