Oxygen aided photoresponse enhancement of air-stable PbSe quantum dot based photoconductors

The recent success of the surface passivation of lead chalcogenide quantum dots for enhancing ambient stability offers further investigation of surface states in air. Here we studied the photoresponses due to surface passivation and oxygen, thus providing the relations of surface states and the photoresponse of PbSe QD films by monitoring the changes in QD film with air exposure. A dramatic near-infrared photoresponse was observed when the PbSe film stabilized through surface passivation was exposed to air. As a result of estimating the density of trap states from the FET characteristics, it was confirmed that the iodide-passivated PbSe film exposed to the air had more trap states than the nitrogen atmosphere. The increase of the trap state due to oxygen adsorption led to the increase of the trap-captured photogenerated electrons, which increased the photoconduction gain. Even though some trap states have a negative impact on device parameters such as charge mobility and response time, controlling the oxygen-related trap states on QD surface is expected to enhance the photoresponsivity on the QD-based photoconductive films without performance degradation in air.