| Quantum Dots?QDs?is a kind of quasi-zero dimensional semiconductor nanostructure material.In recent years,due to its excellent optical properties:high photoluminescence quantum yield?PLQY?,high luminous color purity,and adjustable emission wavelength etc.,which have attracted extensive attention in the fields of solar cells,anti-counterfeiting tags,fluorescent probe,light-emitting diodes?LEDs?and electronic displays.Especially the performance of Quantum Dot Light-emitting Diodes?QLEDs?is constantly improving with the development and improvement of QDs optoelectronic application technology,which has caused a wave of research on QDs technology and its optoelectronic applications.However,the related technology level still lags behind the requirements of commercial applications,and the imbalance of electron/hole injection in devices has become a bottleneck in improving the efficiency and life of QLEDs.On the other hand,most of the QDs in high-efficiency QLEDs contain cadmium,which limits the further commercial application of QDs technology.Because of the non-toxic,environmental friendly and wide fluorescence spectrum coverage,In P QDs is regarded as a strong candidate for cadmium based QDs.However,In P QDs still have many disadvantages,especially the low PLQY and poor size uniformity greatly affect the development and application of In P QDs,and the sensitivity of In P QDs to high temperature will make the design of QLEDs more difficult.Therefore,improving the quality of In P QDs and the performance of QLEDs is the key to the large-scale commercial application of QDs technology,and the main work of this paper is as follows:1.First of all,based on the inverted QLEDs structure,we determined that the charge transfer/injection imbalance has a great influence on the performance of QLEDs through a lot of experiments.And then we found that the root cause of the device charge imbalance is that the efficiency of hole injection in QLEDs is significantly lower than that of electron injection.At last,the reason of low hole injection efficiency is analyzed from three directions of film thickness,energy level matching and carrier mobility,which lays a foundation for the study of promoting charge balance of QLEDs.2.1,3-bis?9H-pyrido[2,3-b]indol-9-yl?benzene?m Ca P?as a new type material of hole transport layer was introduced,which has high hole mobility and deep highest occupied molecular orbital?HOMO?.When it was applied in QLEDs,the large injection barrier between the hole injection layer?HIL?and the hole transport layer?HTL?was found,which affect the efficiency of hole injection.Therefore,we design the stepwise bi-layer HTLs with deep HOMO level,which can not only make energy level of QLEDs well-matching,but also can effectively improve the hole injection efficiency,and thus significantly improving the charge balance in QLEDs devices.The resulting green QLEDs show a maximum current efficiency?CE?of 41.2 cd A-1corresponding to an external quantum efficiency?EQE?of 12.6%,and meanwhile the operational lifetime was increased by more than twofold,which is a significant efficiency enhancement compared with the devices with only single-layer HTL.3.First of all,in view of the low luminous efficiency and uneven size distribution of In P-based core-shell QDs,based on the existence and unique properties of magic size cluster?MSC?during the growth of In P QDs,and combined with the alloy transition layer to reduce core-shell interface tension and defects,a new preparation scheme for In P QDs was developed.The In P/Zn Se/Zn S QDs were synthesized with high PLQY?81%?and the emission peak full-width at half-maximum?FWHM?of 36 nm.Finally,the In P QDs was applied to QLEDs,and the resulting In P-QLEDs shown the highest luminance of 2230 cd m-2and the maximum EQE of 3.6%... |
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