Operando Investigation of the Aging Mechanism of Lead Sulfide Colloidal Quantum Dots in an Oxidizing Background

Lead sulfide (PbS) is a p-type semiconductor that is often applied in photodetectors and solar cells. One major problem that researchers are regularly confronted with is the loss of performance when operated in air. The sensitivity to the ambient, however, makes it an interesting material for the application in gas sensors. Although a lot of research has been focused on the aging of PbS, the influencing factors and the associated material changes are still a matter of debate. Resistance measurements of differently prepared PbS samples operated as sensors for the detection of NO2 (a strongly oxidative gas) in combination with surface-sensitive methods (diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy) enabled the investigation of the changes associated with aging and their influence on the sensing mechanism. The aging mechanism was found to be predominantly influenced by the presence of residuals of the stabilizing agent oleic acid that was adsorbed at the surface of the colloidal quantum dots. Additionally, it was found that a byproduct of the consumption of oleic acid enhanced the detected sensor signal.