Investigation On High Performance Perovskite Light-Emitting Diode

In recent years,a lot of attention have been focused on perovskite light-emitting diodes,which was caused advantages of perovskite materials including low cost,high color purity,easy to process and tunable band gap.At present,external quantum efficiency?EQE?of PeLED reached 14.3%,which was equal to traditional organic emitting diodes.However,there are others problem need to be solved.For example,the stability of PeLED have not been solved and the brightness and efficiency of PeLED still need to be increased.On the other hand,most of PeLED exhibited monochromatic light while white light was compound light.So if white PeLED are to be realized,the full-emission of three-primary color will need to be realized in emitting layer.Up to now,no report about white PeLED was reported,which are key factors of influencing commercialization.In this paper,the PeLED were fabricated on the premise of solution method.First,ideal white PeLEDs were fabricated by one-step spin-coating technology.Second,a green PeLED with high efficiency and high brightness based MAPbBr₃ and CsPbBr₃ was achieved by improving the films coverage of the perovskite emitting layer and carriers injection transporting.The major contents of chapters will be summarized as follows:In chapter 1:First,the emergence of PeLED were introduced.Next,the basic situation of PeLED was described including perovskite material,process technology and the latest research progress and development tendency in the future.At last,the major search purpose and the contents of paper were stated in detail.In chapter 2:A novel precursor solution processed method was adopted to fabricated high quality perovskite films where grain coverage rate reached 100%,which improved films coverage rate and simultaneously improved carriers injection balance.On one hand,since the MAPbBr₃ solution can be dissolved in DMF not in toluene and the two solvent were mutually soluble,the toluene was added into the precursor solution to reduce the perovskite solubility in DMF and to accelerate the perovskite crystalline rate during spin-coating enhancing the film coverage.On the other hand,the electron transporting material TPBi and the hole transporting material PVK were doped into the precursor solution.By adjusting the weight ratio of those two material,the electron and hole injection balance can be optimized leading to improve device performance.Consequently,the optimal PeLED exhibited the turn on voltage of 2.8 V,maximum luminance of 7263 cd/m²,maximum current efficiency of 9.45 cd/A.In chapter 3:Based on the previous research,we continued optimizing preparation methods to improve devices performance.Specifically,the Au NPs was incorporated into the hole injection layer of PEDOT:PSS,utilizing localized surface plasma resonance,to quicken exciton emission radiation rate at the interface between PEDOT:PSS and MAPbBr₃,which decreased the number of interface exciton quenching caused by nearly remained carriers?holes?to make more exciton use efficiency.It was found that,after the Au NPs incorporated,both photoluminescence and electroluminescence performance of MAPbBr₃ perovskite films were distinctly improved.Compared to the reference device,2.4 times and 1.5 times were enhanced.The optimal PeLED fabricated gave the maximum luminance of 16060 cd/m² with turn on voltage of 3.0 V,and maximum current efficiency of 7.02 cd/A.In chapter 4:Researching on CsPbBr₃ PeLED,the phosphor material FIrpic was adopted into the electron transporting layer of TmPyPB in a certain proportion.Because there was a large-scale overlap between the absorption of all-inorganic CsPbBr3 and the emission spectrum of FIrpic and the energy level matched well leading Foster energy transfer between them,exciton use ratio can be greatly boosted thus improving devices performance.Consequently,the optimal device adopted showed the maximum luminance of 14363 cd/m²,maximum current efficiency of 4.9 cd/A,and the turn on voltage of 3.4V,which was 3.5 times and 4.8 times,respectively,comparing to the reference device.In chapter 5:PeLED based CH₃NH₃⁺?MA⁺?system were fabricated by utilizing mCP and MAPbBr₃ mixed solution spin-coating as emitting layer,which exhibited ideal white light.It was found that,due to adding molecule material mCP into MAPBbr₃precursor solution in various ratio,the coverage rate of films was improved effectively and the radiation of full spectrum can also be achieved,where part of the blue-violet light and green light came from the intrinsic radiation of the mCP and MAPbBr₃ while part of red light may come from the exciplex between the mCP and MAPbBr₃.In the end,The white PeLED exhibited the turn-on voltage of³.2 V,the maximum luminance of¹70cd/m²,and the EL efficiency of⁰.15 cd/A.At a driving voltage of 7 V,we got white emission with CIE coordinated at?0.32,0.31?,indicating the white light was ideal.Such white PeLED can meet the basical requirements.