Study On Fluorescent Oxygen Sensor Based On All-inorganic Halide Perovskite

Oxygen monitoring is of great significance in the fields of biology,medicine,transportation,agriculture,engineering,and the environment,and has been widely concerned by researchers for a long time.Among them,optical oxygen sensors have become a competitive detection method due to their low invasion and good repeatability.In recent years,hybrid and inorganic halide perovskite have attracted great interest as a promising new photoelectric semiconductor material.The material has the characteristics of adjustable band gap,high carrier mobility,high diffusion coefficient and low exciton binding energy.At the same time,it is highly sensitive to changes in gas environment,showing great application potential in the field of oxygen sensing.Although they exhibit some sensitivity to oxygen,the unstable crystal structure and the hygroscopicity of organic cations lead to poor stability of organic halide perovskite.Therefore,it is crucial to develop oxygen sensors based on halide perovskite with high sensitivity and long-term stability.In this paper,a fluorescence oxygen sensor based on inorganic halide perovskite CsPbBr₃and lead-free halide perovskite Cs₂AgBiBr₆is constructed and its sensing properties and mechanism are explored,aiming to promote the research and application of halide perovskite in the field of oxygen sensing.It mainly includes the following contents:（1）To solve the problem of poor stability of organic-inorganic hybrid halide perovskite,inorganic halide perovskite CsPbBr₃with better stability was used as oxygen sensing material.CsPbBr₃thin films and CsPbBr₃nanocrystals（CsPbBr₃NCs）were prepared by spin coating method and hot injection method respectively,and they were used in the preparation of fluorescence oxygen sensor.It was found that CsPbBr₃film achieved a response value of 0.18 and a response/recovery time of 56/339 s to the change of 2%O₂concentration.The lowest O₂detection limit was 500 ppm.After exposure at 85%relative humidity（RH）for 28 minutes,the photoluminescence integral intensity of CsPbBr₃film remained about 75%of the initial value,indicating that the perovskite halide had good humidity stability.In order to further improve the performance of the sensor,CsPbBr₃NCs were synthesized by hot injection method and made into a fluorescent oxygen sensor.It was found that the nanocrystalline oxygen sensor achieved faster response recovery times of 19 s and 63 s（2%O₂）,respectively,as well as higher sensitivity with a minimum detection limit of 100 ppm O₂,a five-fold increase in sensitivity compared to the CsPbBr₃thin film oxygen sensor.The above results indicate that compared with CsPbBr₃thin film,CsPbBr₃NCs oxygen sensor shows better oxygen sensing characteristics,which may be due to the smaller nanocrystalline size and more adsorption sites per unit area than CsPbBr₃thin film.（2）In order to solve the toxicity problem of lead halide perovskite,lead-free halide perovskite Cs₂AgBiBr₆was first used as a fluorescent oxygen sensing material.The lead-free halide perovskite Cs₂AgBiBr₆thin film was successfully prepared by spin coating method.The effects of four different precursor concentrations and five antisolvents on the morphology and oxygen sensing performance of the film were investigated.It was found that when the precursor concentration was 0.6 mol L^-1and the antisolvent was toluene,the prepared thin film had a relatively uniform porous morphology and the highest response value to oxygen,to prepare for the subsequent construction of this lead-free halide perovskite Cs₂AgBiBr₆as an oxygen sensor.（3）The performance of lead-free halide double perovskite oxygen sensor Cs₂AgBiBr₆was studied systematically.The sensor exhibits good selectivity,high sensitivity,and rapid response to oxygen,as well as excellent long-term stability.After two weeks of storage in an unpackaged environment,it still maintains the ability to detect low concentrations of oxygen.At the same time,it also has good humidity stability.After exposure to 90%RH for 70 minutes,the PL intensity still maintains92%of the initial value;Light stability,the PL intensity remained stable after 60minutes of 405 nm excitation light irradiation;Thermal stability,the PL can maintain96%of the initial intensity during heating/cooling cycles of 20-60°C.And compared with other halide perovskite fluorescence oxygen sensors,it is found that Cs₂AgBiBr₆oxygen sensor has excellent performance in stability.In addition,the mechanism of interaction between O₂and Cs₂AgBiBr₆thin films was further analyzed by in-situ near-atmospheric X-ray photoelectron spectroscopy.It was found that spontaneous desorption of Br₂resulted in a large amount of V_Brin Cs₂AgBiBr₆thin films,leading to weak PL intensity.When Cs₂AgBiBr₆thin film is exposed to oxygen atmosphere,O₂molecules will fill V_Brand form a superoxide（₂+^-=₂^-）with local excess electrons,passivating the defect of trapping photogenerated holes,leading to increase in PL intensity.Based on the above results,this environmentally friendly lead-free halide perovskite has great potential in the field of oxygen sensing.