Control Of Luminous Properties Of CsPbBr₃ Quantum Dots

Fully inorganic lead halide perovskite（Cs Pb X₃,X=Cl,Br,I）quantum dots（QDs）,due to their adjustable spectrum,narrower half-width,higher defect tolerance and solution processability An emerging photoelectric material,but due to the problem of low efficiency,it cannot meet the actual requirements.The main problem facing Cs Pb X₃ QDs PL regulation is the instability of the mixed halogen QDs spectrum due to ion migration.At the same time,for the blue light emission through the way of mixing halogens,the introduction of Cl will lead to the formation of deep level defects,which will inevitably lead to the reduction of PLQY.Improvement is the key to the problem,Cs Pb X₃ QDs surface defect passivation.The main problem faced by QY is the contradiction between the sensitivity of perovskite to polar solvents and the need for polar solvents to pass the passivating agent.Therefore,although the reported methods are diverse,the choices of passivating agents,reaction conditions,etc.are still very limited,and lack of universal methods.We propose a new surface treatment method for CsPbBr₃ QDs,which not only overcomes the contradictory problem that perovskite quantum dots are easily decomposed by polar solvents but short-chain organic ammonium halide（C≤4）requires polar solvents to provide a certain solubility The solvent used in the purification process is methyl acetate（Me OAc）.The weak polarity of Me OAc can ensure that CsPbBr₃ QDs are not decomposed.At the same time,most of the short-chain ammonium bromide has a certain degree of solubility in Me OAc and therefore has a certain universal.Moreover,this method is not only convenient and quick,but also has certain universality for short-chain organic ammonium salts.We prove this feature of the method by using three short-chain ammonium bromides with different carbon numbers as DMABr,IPABr,and t-BABr.The solvent is used as a passivating agent and end-capping agent,which can simultaneously achieve the passivation of surface defects.Chemical and ligand exchange without destroying the structure of quantum dots.The optical performance test results show that the colloid of the surface-treated CsPbBr₃ QDs and the PLQY of the film have been greatly improved,the colloid from the initial 49%to 95%,and the film from the initial 18%To 68%.Both TEM and XRD indicate that the treated CsPbBr₃ QDs solution is dispersed and closely arranged,and still maintains the cubic crystal phase.Then we constructed a QLED device based on CsPbBr₃ QDs before and after surface treatment and conducted a series of tests.The data shows that the QLED device based on the processed CsPbBr₃ QDs is better in terms of maximum brightness,maximum current efficiency and maximum power efficiency.Among them,the CsPbBr₃ QLED treated with 20%t-BABr has the best performance,which proves that This method significantly promotes the carrier injection efficiency of quantum dot films.Further,surface optimization is carried out by using different ammonium chloride salts containing the initial CsPbBr₃,so as to realize the emission spectrum control from the green light to the blue light region while improving its fluorescence quantum yield.Also add a small amount of short-chain organic ammonium chloride（C<=4）to Me OAc.Since a small amount of Cl^-mainly acts on the surface of CsPbBr₃ QDs,it is possible to avoid the formation of deep defects in the band gap,thereby achieving QY enhancement and PL blue shift.The results show that the CsPbBr₃ QDs not only have a great improvement in PLQY after 2-BACl treatment,but also have the most blue shift to the short wavelength.When the ratio of[Cl^-]_added/[Br^-]_initialis very small（0.3）,deep blue quantum dots can be obtained,and the solution of the obtained blue quantum dots and the PLQY of the thin film have both Improvement,finally using CsPbBr₃ QDs treated with 25%2-BACl as the light emitting layer of QLED,the standard blue EL is459 nm,the maximum brightness is 76 cd m^-2,and the EQE is 0.3%.