Controlled Preparation And Properties Of CH₃NH₃PbBr₃ Quantum Dots

Lead halide perovskite quantum dots（QDs）are known as promising optoelectronic device materials because of their excellent luminescence,extraordinary photoelectric performance,and specific octahedrons framework.They’re extensively used in light emitting diodes,solar cells,and lasers.However,perovskite QDs are extremely sensitive to oxygen,moisture,and UV light in the environment,making their structures easy to resolve and then affecting their application performance.And common preparation methods involve complicated processes and demanding requirement.Based on their varying sensitivity and solubility in different polar solvents,we use a simple,mild,and easy-to-operate binary solvent method to directly synthesize size adjustable and color tunable QDs with emission spectra encompassing the full visible spectrum.The effects of the solvent mixture ratio,dosage,surface ligand ratio,and reaction temperature on the preparation process were primarily studied.The probable synthesis mechanism was analyzed,and the products were applied to white light emitting diodes（WLEDs）.The main contents are summarized as follows.1.The preparation of perovskite QDs using low-polarity solvents was proposed with the goal of producing very stable products.To investigate the effects of solvents with different polarities on the product,eight solvents with different polarities,such as cyclohexane and butyl acetate,were chosen,.And the best reaction solvent combination was determined to be a mixture of cyclohexane and tetrahydrofuran.The synthesized QDs feature a single,crisp PL spectrum with a quantum yield of up to 90%and a yield of 85%.The final product has excellent stability,with no noticeable reduction in quantum yield after five days in the air.After 20 days of storage in screw-top bottles,no significant changes in PL,and precipitation were unobserved.A proposed synthetic mechanism for low-polarity solvent combinations’protective effect in the synthesis of QDs has been investigated.Solvent molecules are involved in the crystallization of QDs and form solvent complexes with the reactants,slowing down the reaction rate.2.Based on the above study,a binary solvent method using cyclohexane and tetrahydrofuran as a mixed solution is proposed to prepare CH₃NH₃PbBr₃QDs.The optimum preparation conditions were investigated:tetrahydrofuran:cyclohexane=1:4,10 m L of solvent,108 L of OA,60℃,and PbBr₂:CH₃NH₃Br=2.5:1.By adjusting the ratio of OA and OAm ligands,QDs with particle sizes ranging from 1.2 nm to 4.2 nm could be prepared.The synthesized quantum dots have a single sharp emission peak with a half-peak width of 24 nm and a luminous lifetime of up to 150 ns.By adjusting the halogen group elements in the reactants,the method can also be extended to the preparation of QDs in the entire visible range,with an emission spectrum ranging from 450 nm to 700 nm.The resulting green-emitting CH₃NH₃PbBr₃ QDs were combined with commercially available red fluorescent powder and blue chips to produce WLED with a color coordinate of（0.3411,0.3454）,a maximum brightness of6000 cd m^-2,and a maximum power efficiency（PE）of 56.6 lmW^-1.