Photoconductivity studies of treated CdSe quantum dot films exhibiting increased exciton ionization efficiency

We present measurements of photoconductivity in CdSe quantum dot films treated with a variety of reagents. While the photocurrent of untreated samples is highly voltage dependent at all voltages, after treatment the photocurrent is much larger, depends strongly on voltage at low voltage, displays a linear region above a voltage threshold, and finally saturates at high voltage. All regions of the current-voltage curves after treatment can be reproduced with a model that requires noninjecting contacts and a field dependent exciton ionization efficiency that saturates to unity. This model is shown to be consistent with the trends observed with different treatments. The changes in photocurrent with treatment are shown to be largely a consequence of increased quantum dot surface passivation and decreased quantum dot spacing, regardless of whether the molecules used for treatment are conjugated or able to cross-link the quantum dots.