PbS colloidal quantum dot photoconductive photodetectors: Transport, traps, and gain

We investigate experimentally the origins of gain in PbS colloidal quantum dot photodetectors. We employ measurements of photocurrent, its transient behavior, and dark current over a wide range of temperatures. We find the hole mobility to have an activation energy of 0.16eV, and we identify photosensitizing centers at ∼0.1, 0.2, and 0.3eV below the conduction band edge. These centers account for the 60, 300, and 2000ms fall times observed in the transient response of the photocurrent at room temperature. These centers enable us to account for the constancy of photoconductive gain across the wide temperature range of 250–340K.