Green Inverted Quantum Dots Light-emitting Diode Devices Fabricated Via All-solutionprocess Based On CdSe@ZnS Quantum Dots

Quantum Dots(QDs)have been applied in various of scientific research fieldssuch as photoelectricity and biology due to the special advantages in wide absorption spectrum,narrow emission band-gap,high contrast ratio and color saturation.Centering on the QDs,QuantumDots Light-Emmiting Diodes(QLED)have been caused extensive attentions in the application of lighting and display increasingly and achieved rapid developments accordingly.Inverted architecture is proposed and designed because it can be more suitable for display applications with its transparent substrate can be integrated with n-type metal-oxide or amorphous-silicon thin film transistor,and after years of research,perfomances of the inverted QLED have obtained tremendous progress.Currently,the holetransport layer and the holeinjection layer of the inverted QLED are ordinarilydeposited through thermal evaporation method in high vacuum condition,which is constrained with multiple parameters and faced with high-cost materials and compiex manual operating skills.Therefore,it is really practical and reliable to adopt a simple method can be deposited on large area and with low-cost materials simultaneously.As we all know,solution-process method is frequently utilized in the QLEDs with normal structure,which contains the advantages such as simple operation process,low-cost materials and availablely spin-coated on large area.Concerning the current investigative state about the QLEDs manufactured via all-solution process.This report is mainly centreing on the solution-process method to manufacture a green inverted QLEDs devices and develop corresponding works.Pointing on the issues that solvent damage underlayer,hydrophobicity between the interface of different materials,high current density and fluorescence decay in fabricated devices during the process,The main contents of this thesis are as follows:1.Optimizing and controling the perfomances of inverted QLEDs through orthogomal solvents:(1)During the process,there exsists a highly hydrophobic surface on the PVK layer for the hydrosoluble PEDOT:PSS,caused the high contact angle and hardly depositing on the PVK layer,which leading to a poor perfomance of the devices.Pointing on this issue,we treated the PEDOT:PSS disperse with hydrophilic isopropanol stirring by appropriated ratio to enhance its adhesion on the surface of PVK layer,after that,the quantity of the PEDOT:PSS layer and the perfomance of the devices are remarkably developed overall.We eventually obtain the devices of maximum luminance of 6918 cd/m~2,maximum current efficiency of 6.33 cd/A,and maximum external quantum efficiency of 1.52%respectively.(2)Accounting for the solvent of PVK(m-xylene)can dissolve QDs ultimately,so it is inevitable that there will be a indeed damage underlayer after PVK is spin-coated on the QDs layer.And it is impactful to weaken this damage to use an orthogonal solvents of PVK relative to the QDs.In our reports,we adopt different kinds of solvents of PVK and and contrast the fluorescence decay and device performance after spin-coated on the QDs layer reciprocallyand we choose the chlorobenzene as the most optimized solvent and obtain the best performance.We eventually get the devices of maximum luminance of 24730 cd/m~2,maximum current efficiency of 21.51 cd/A,maximum power efficiency of 12.28 lm/W and maximum external quantum efficiency of 5.88%respectively.2.Promoting the efficiency ulteriorly through annealing the QDs layer and inserting a electron blocking layer(1)We further the optimizational process via annealing the QDs layer and boost the Current efficiency dramatically,the optimized current efficiency and the highest calculated EQE shows24.29 cd/A and5.75%respectively,and in especial there is a enhancement of 104.6%in current efficiency comparing with the QDs without annealing process.We analysis this enhancement by annealing process to alter the surfacial morphology of QDs layeror lead to a desorption of the ligands bounded on the surface of the QDs.We characterize the integral QDs layer annealed at different temperature with Atomic Force Microscope and exclude that annealing process can effect on the exterior morphology accounting for the unchanged roughness of the integral QDs layer after annealing.Finally,annealing process of the QDs layerleading to a probable ligand desorption and smoothing the injected efficiency of the charge carriers,so that there is a remarkably boost of current efficiency.(2)Pointing on that a really higher current density and low current efficiency,we insert a thin PVK layer which owns a high LUMO level between the ZnO and QDs as an electron blocking layer to block the electrons and balance the carriers,and we get a current efficiency of 20.7 cd/A from the EBL devices which has promoted the current efficiency by 43.7%,and a luminance of 26070 cd/m~2boosted by 28.2%contrast with the control devices ultimately,the inserted electron blocking layer achieved the purpose of depressing the current density and boosting the current efficiency.