Resistive gas sensors based on colloidal quantum dot (CQD) solids for hydrogen sulfide detection

Colloidal quantum dot (CQD) is emerging as new substitution gas sensing materials due to the excellent accessibility of gas molecules to CQD surfaces realized via surface ligand removal. Here we demonstrated highly sensitive and selective H₂S gas sensors based on PbS CQD solids. The sensor resistance decreases upon H₂S gas exposure and the response is defined as the ratio of the sensor resistance in clean air to that in H₂S gas. As the operating temperature increased within the range 50-135 °C, the sensor response increased while the response and the recovery time decreased. The sensor was fully recoverable toward 50 ppm of H₂S at 108 °C and the highest response was 2389 at 135 °C with the response and recovery time being 54 s and 237 s, respectively. The dependence of sensor response on the H₂S gas concentration in the range of 10-50 ppm is linear, suggesting a theoretical detection limit of 17 ppb toward H₂S at 135 °C. Meanwhile, the sensor showed superb response selectivity toward H₂S against SO₂, NO₂ and NH₃. We propose that the PbS CQDs film where the surface states determine the conduction type via remote doping may undergo a p-to-n transition due to H₂S exposure at elevated temperatures.