Our group's previous research has focused on the synthesis of perovskite and InP quantum dots and their application in light-emitting diodes. Now the group would like to apply the quantum dots research results in the sensing of malodorous gases (e.g. hydrogen sulfide, ammonia, etc.), preferably resistive sensors or electrochemical sensors.

I initially synthesized red-light InP/ZnSe quantum dots and spin-coated them directly onto silicon substrates deposited with gold-forked finger electrodes after ligand-exchange with ZnCl2, and tested them for gas sensitivity. The gas sensitivity test will be performed with violet light excitation of the material. The result of the test was that the CV curve was very unstable, with no significant response to both NH3 and H2S and high noise.

Later, I referred to the literature related to quantum dots for photodetectors, solar cells, etc., and wanted to learn from the experience in these fields to improve the performance of charge extraction and electrical transport. Since InP/ZnSe quantum dots and ZnO show type II energy band structure, and ZnO is a commonly used electron transport layer in LEDs, and ZnO is also one of the most researched materials for H2S as well as NO2 gas sensing. Therefore, I made some improvements: I now spin-coated ZnO on a silicon substrate and annealed it, then spin-coated InP/ZnSe quantum dots exchanged with ZnCl2 ligand, and then performed gas sensitivity tests. This time, the samples showed a more stable CV curve as well as a uniformly varying current, but were still unresponsive to NO2 gas.

Therefore, I believe that my study still has not overcome the difficulties in charge extraction and electrical transport due to the domain-limiting effect of quantum dots and the high density of surface ligands. In more details, the photogenerated carriers generated by quantum dots still tend to be compounded rather than transported outward, while the quantum dots themselves are highly resistive materials, and the large number of organic ligands to maintain the stability of the surface of the quantum dots further hinders the charge transport. These are also key issues that need to be addressed for quantum dots to be used in gas sensing.

I would like to ask if there is any better research or improvement ideas to better modify and use quantum dots as gas sensors, or to combine quantum dots with other gas-sensitive materials?