Grain Size-Engineering of PbS Colloidal Quantum Dots-Based NO2 Gas Sensor

The large surface-to-volume ratio and highly reactive surfaces, combined with solution-processability make colloidal quantum dots (CQDs) promising to be the next generation of gas-sensing materials. However, the size- engineering gas-sensing behavior of CQDs has not been further studied. Herein, we report the controllable synthesis of PbS CQDs with diameter sizes ranging from 2.7-7.0 nm through adjusting the injection temperature, precursor concentration and cooling rate. The results showed that the method of cold bath cooling exposed more {100} facets and enhanced NO
₂
-sensing properties at room temperature. According to the first principle calculation, the {100} facets of PbS CQDs favors the competitive adsorption of NO
₂
with O
₂
molecules, which is in contrast with the {111} facets. At the same time, rapid cooling rate helps to increase the density of intra-band trap states of PbS CQDs, which may favor the interdot carrier hopping so as to transduce the charge transfer during the competitive adsorption between NO
₂
and O
₂
molecules into enhanced electrical current. This work reveals the microstructural mechanism underlying the size engineering of CQDs-based gas sensors.