Stability Analysis Of Perovskite Quantum Dots And LED Applications

With the improvement of people’s living standards,lighting has become an essential part of life,and the pursuit of efficient white light has become an important task for white light-emitting diodes（WLEDs）.At this stage,perovskite（Cs Pb X₃）has a broad application in solar cells,lasers,and lighting due to its tunable optical bandgap and high photoluminescence（PL）quantum yield（QY）.However,perovskite also has some disadvantages:the red-emitting perovskite containing I is unstable,the PL QY for the blue-emitting perovskite containing Cl is low,and because of the anion exchange reaction,WLEDs made from perovskites containing Cl,Br,and I anions have poor color stability.In view of the above problems for the perovskite quantum dots（QDs）,this paper designs and develops new types of perovskites with improved luminous efficiency and stability,and puts forward strategies for achieving WLEDs of high color rendering index（CRI）using blue,green,red perovskite materials having the same halogen Br anion to avoid the anion exchange between different perovskite materials,and effectively improve the stability of the WLEDs.The details are as follows:（1）The feasibility of using non-toxic and environmental friendly carbon dots（CDs）to replace low-efficiency Cl-containing blue-emitting perovskite and Mn-doped Cs Pb Cl₃ to replace I-containing red-emitting perovskite with poor stability to prepare WLED is explored.By dissolving solid anhydrous citric acid into anhydrous ethanol to form a source solution,a simple and safe method was developed to synthesize blue-emitting CDs with high PL QY.At the same time,orange-emitting Cs Pb_0.81Mn_0.19Cl₃ QDs with high stability and high PL QY were developed.Since there are no halogen ions in CDs,there will be no anion exchange reaction when the two are mixed,so the WLED prepared based on this shows good color stability when the driving current increases.（2）For the first time,Mn doped two-dimensional（2D）phenylethylamine,lead-bromine perovskite（PEA₂Pb Br₄）nanoplatelets（NLs）with high PL QY（～97%）were designed and synthesized,and their optical properties were systematically studied.We find that the crystal field rather than Mn-Mn interaction is responsible for the red shift of Mn ion emission.Therefore,the luminescence peak is mainly determined by the content of PEA rather than that of Mn.At the same time,the PEA₂Pb_0.74Mn_0.26Br₄ maintained the stability of the 2D structure of perovskite,and its PL QY and crystal structure remained unchanged in the natural environment for more than 300 days.After 350 hours of continuous operation at 20 m A,the luminescence intensity of the device was maintained at 90%of the original value.（3）A technical scheme was proposed to prepare WLEDs with high stability by using blue,green and red perovskites all with Br anions.Blue-emitting Cs Pb Br₃ NLs was prepared and its PL QY was effectively improved by adding Pb Br₂ solution to passivate the surface of the NLs.Highly efficient and highly stable Mn doped red-emitting PEA₂Pb Br₄and green-emitting Cs Pb Br₃ QDs were optimized and prepared.The performance of high CRI and high stability WLED made from the developed three color perovskites and a UV LED chip as excitation light source was studied.It was verified that because these three perovskites have the same halogen Br anion,no anion exchange reaction had occurred.By adjusting the amount of these three kinds of perovskites,WLED devices with different color temperatures from"cold"white light to"warm"white light were realized,with the highest CRI reaching 94.In addition,the prepared WLED has good stability as the driving current increases.