Synthesis And Thermal Stability Of CsPbBr₃ Quantum Dots In Octadecene/1,3,5-trimethylbenzene Mixed Solvent

In recent years,inorganic halide perovskite quantum dots（QDs）have attracted much attention because of their high fluorescence quantum yield,narrow full width at half maximum（FWHM）,tunable bandgaps across the visible spectrum（400–800 nm）and simple synthesis process,becoming one of the research hotspots in the field of optoelectronic devices.One of the biggest challenges of QDs for practical applications is its purification and storage stability.The traditional ligands are easy to fall off during purification or storage,which leads to the aggregation and growth of QDs and the decrease of quatumn yield.At present,CsPbBr₃ quantum dots prepared by single ligand benzenesulfonic acid have high quantum yield（>90%）,and the quantum dots can maintain good stability after multiple purifications and long-term storage.But there are several problems with this system:1.The precursor TOAB can not dissolve completely in toluene solvent,which affects the full coordination between Br and Pb.2.The low boiling point of toluene limits the reaction temperature,leading to low reaction activity and low yield of QDs.Therefore,some shortcomings in the preparation of qds have been improved by replacing the bromine source with DDAB/DODMAB and the solvent with higher boiling point 1,3,5-trimethylbenzene.In the presence of octadecene/1,3,5-trimethylbenzene mixed solvents,the yield improvement of QDs was studied from the commercial cost point of view,then,a series of work was carried out on the thermal stability in practical application.The main research results are as follows:（1）A dialkane bromide source DDAB and a higher boiling point 1,3,5-trimethylbenzene solvent were used to replace the original system.After purified many times and stored for a long time,the CsPbBr₃ quantum dots synthesized by the mixed solvent system remained the fluorescence emission center and half-height width of the quantum dots unchanged and the quantum yeild was still close to 1,indicating that the quantum dots had excellent optical stability.At the same time,on the basis of ensuring the quality of quantum dots,the yield of quantum dots under the mixed solvent system reached 70%.The amount of bromine source has an important influence on the yield of quantum dots.It was found that when the injection amount was adjusted to 1.4 m L,the yield of quantum dots increased to 80%.In addition,by regulating the types of bromine sources,we found that for both DDAB and DODMAB bromine sources that belong to the same dialkane chain,the quantum dots maintain nearly100%of quantum yield.And at the same time,both had high yield in the range of 65%～70%.（2）The thermal stability of QDs was studied under mixed solvent reaction conditions based on DODMAB as bromine source.Firstly,the thermal stability of the prepared quantum dots for various periods of time with different bromine sources under long-term high temperature was compared.It was found that DO-QDs synthesized by DOMAB maintained the stability of optical properties and dimensional structure during the reaction at 150 ^oC for 2hours.Then we studied the factors that affect the thermal stability of quantum dots from two aspects:the reaction temperature and the amount of the A-site cation Cs.Under the different reaction time of each reaction temperature,the fluorescence center of DO-QDs were constant.The addition of Cs,the A-site cation,affected the stability of DO-QDs’optical properties under high temperature and long-term reaction.Only excessive Cs ensured the DO-QDs’fluorescence center and absorption peak unchanged under this condition.In order to study the possibility of single-core-shell coating of DO-QDs,we used different boiling point solvents to further increase the reaction temperature to observe the thermal stability limit of DO-QDs.When DO-QDs reacted at 200 ^oC for 2h in ODE solution,the optical properties remained unchanged and the quantum yield was 86.9%.Then different coating precursors were added to the ODE solution of DO-QDs for high temperature and long time reaction.It was found that the addition of Zn OA/TOPS could keep the phase structure and optical properties of DO-QDs stable,providing the experimental basis for the sythesis of DO-QDs@Zn S structure.Finally,in order to improve the fluorescence process of DO-QDs,a small amount of OA was used to eliminate the surface defects and achieved single exponential fluorescence decay of QDs.