Prof. Zhan Yiqiang group from School of Information Science and Engineering in Fudan University has developed the humidity sensor with superfast recovery speed based on the lead-free Cs₂BiAgBr₆ double perovskite. On April 15, the research results were published in Advanced Functional Materials (IF:15.6, 10.1002/adfm.201902234) under the title of “Lead Free Cs₂BiAgBr₆ Double Perovskite Based Humidity Sensor with Superfast Recovery Time”. In the research of humidity response of perovskite, the group has innovatively revealed a kind of humidity sensitive mechanism which is totally different from the interaction between traditional perovskite materials and water molecules - reversible physical adsorption and desorption. This research result will bring a very broad application prospect for lead-free double perovskite materials in the field of humidity response.

Figure 1 Response curve and mechanism of humidity response

Cs₂BiAgBr₆ is a kind of newly developed lead-free perovskite with good photoelectric property and high stability. During the research of Cs₂BiAgBr₆, Zhan Yiqiang's group found that the material has excellent humidity sensitivity. By analyzing the humidity response of the material at different temperatures, the group found that the adsorption effect of water molecules on the surface of perovskite is the main humidity-sensitive mechanism. The humidity sensor based on lead-free double perovskite show a high performance, whose response and recovery speed can reach 1.78s and 0.45s, which is faster than the response speed of traditional ceramic oxide humidity sensor (~ 10s). This ultra-fast response humidity sensor will have a wide application prospect in medical respiratory monitoring, cell culture humidity monitoring and etc.

Figure 2 (a) Impedance spectra of humidity sensors at different humidity; (b) Capacitance curves of humidity sensors with voltage frequency under different humidity; (c-d) Absorption and proton conductivity of water molecules at different humidity.