Sensitive and Stable NO2 Gas Sensors Employing Halogen-Passivated Colloidal Quantum Dots

Lead chalcogenide colloidal quantum dots (CQDs) have the potential to be a new generation of high-performance gas-sensing materials for its high chemical activity, facile solution processability, and size tunability. However, the high chemical activity of CQDs also leads the CQDs to be easily oxidized, which would reduce the long-term stability of CQDs-based gas sensors. Here, we try to introduce halogen ligands in the synthesis of PbS CQDs by using lead halide as precursor. These halogen ligands play a passivate role and are beneficial in improving the long-term stability of PbS CQDs-based gas sensors. Results show that although the PbS CQDs synthesized using lead halide as precursor exhibit relatively low sensor response than that synthesized using traditional lead oxide as precursor, it exhibits faster response and recovery times. More importantly, the sensors employing halogen-passivated PbS CQDs exhibit superior long-term stability, in which more than 80% of their original NO
₂
-sensing performance are still presented after 30 days. It could be attributed to the surface halogen derived from the lead precursor, which prevent CQDs from reacting with the atmosphere and, thus, maintain the oxidative stability of CQDs. This research will pave the way for improving the long-term stability of lead chalcogenide CQDs-based gas sensors.