Highly sensitive and rapid responding humidity sensors based on silver catalyzed Ag2S-TiO2 quantum dots prepared by SILAR

We developed a resistive humidity sensor based on a heterojunction of silver sulfide (Ag2S) quantum dots (QDs) and TiO2 because of its specificity to water vapor adsorption and its insensitivity to environmental gases. The QDs were grown on a mesoporous TiO2 layer using the successive ionic layer adsorption and reaction (SILAR) method. The boundary condition between TiO2 and Ag2S provides a tunable energy gap by adjusting the number of SILAR cycles. Besides, the large surface-to-volume ratio of QDs provides a strong water vapor adsorption ability and electron transfer. Nano-silver precipitated during the SILAR process provides free electrons and lowers the Fermi level to between n-type TiO2 and p-type Ag2S. The resistance response increased significantly to 4600 and the reaction equilibrium time decreased greatly to 7 seconds due to the presence of nano-silver. Finally, the Ag2S QDs possess a best sensing range of 13-90%. To sum up, Ag2S QDs are high sensitivity and selectivity humidity sensors.

Automated summary

The developed resistive humidity sensor based on Ag2S QDs and TiO2 shows high sensitivity and selectivity. The large surface-to-volume ratio of QDs provides strong water vapor adsorption ability and electron transfer, while nano-silver formed during the SILAR process lowers the Fermi level, significantly improving the response time and sensitivity of the sensor.