Abstract
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 sizeengineering 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 NO2-sensing properties at room temperature. According to the first principle calculation, the {100} facets of PbS CQDs favors the competitive adsorption of NO2 with O2 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 NO2 and O2 molecules into enhanced electrical current. This work reveals the microstructural mechanism underlying the size engineering of CQDs-based gas sensors.
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