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

Abstract

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.

In Operando Investigation of the Concentration Dependent NO2 Sensing Mechanism of Bi2S3 Nanorods at Low Temperatures and the Interference of O3

“…The fundamental vibrations of Bi 2 S 3 are at 1120, 868, and 618 cm –1 . − Based on the fundamental vibrations at 868 and 618 cm –1 , overtone vibrations can be expected between 1700 and 1650 cm –1 and between 1200 and 1150 cm –1 , respectively . In case oleyl amine (the organic ligand added during the synthesis as a stabilizing agent) was not fully removed by the ligand exchange during the sensor preparation and it is playing a role in the sensing mechanism (as it was the case for PbS), its typical vibrations need to be considered as well. These vibrations can be found at 1647 (weak), 1593 (medium), 1465 (sharp and strong), and 1071 (sharp) …”

“…In a recent work, we have investigated and discussed in detail the gas sensing performance of PbS colloidal quantum dots (CQDs). We found an impressively fast and reproducible sensor response at room temperature . Unfortunately, the sensor performance showed a severe decrease due to aging which was a result from the reaction between NO 2 and the organic ligand oleic acida residual from the synthesis where oleic acid was added as a stabilizing agent for the CQDs .…”

“…We found an impressively fast and reproducible sensor response at room temperature. 3 Unfortunately, the sensor performance showed a severe decrease due to aging which was a result from the reaction between NO 2 and the organic ligand oleic acid�a residual from the synthesis where oleic acid was added as a stabilizing agent for the CQDs. 3 A byproduct of the reaction between NO 2 and oleic acid was responsible for the high sensor signal in the beginning of the experiment.…”

“…3 Unfortunately, the sensor performance showed a severe decrease due to aging which was a result from the reaction between NO 2 and the organic ligand oleic acid�a residual from the synthesis where oleic acid was added as a stabilizing agent for the CQDs. 3 A byproduct of the reaction between NO 2 and oleic acid was responsible for the high sensor signal in the beginning of the experiment. In operando spectroscopic data showed that without the organic ligand the adsorption of NO 2 on the surface of PbS was responsible for the charge transfer resulting in the observed response; the sensor signal was significantly lower and a constantly increasing baseline resistance as a result of the formation of Pb(NO 3 ) 2 was observed.…”

Solution-processed metal doping of sub-3 nm SnO2 quantum wires for enhanced H2S sensing at low temperature

“…Such small sizes of QDs and QWs offer a surface-dominated structure of abundant surface active sites for electronic and chemical interactions in sensing applications. 19 Recently, SnO 2 QDs 20 and QWs 21 that show low-temperature gas-sensing have been reported, but their selectivity and limit of detection (LOD) are still unsatisfactory for practical applications.…”