Study And Fabrication Of Blue Quantum Dot Light-Emitting Diodes

Over the past few decades,colloidal quantum dot light-emitting diodes?QLEDs?have become a strong contender for new-generation solid-state lighting and displays owing to their important advantages such as size controlled emission wavelengths,narrow emission linewidths,and solution-processability.Since the first report in the1990s,the electroluminescence?EL?efficiency of the QLEDs has been boosted significantly in recent years,which are now competitive to the state-of-the-art organic light emitting diodes?OLEDs?.For instance,a maximum external quantum efficiency?EQE?of 21.5%and 22.9%has been reported for the red and green QLEDs.Moreover,Red and green QLEDs showed a super long operational lifetime suitable for practical applications.Despite the fast development of red and green QLEDs,the performance of blue QLED is far from satisfactory.Inparticular,the lifetime of the blue QLEDs is about only a few thousands of hours.Unlike red and green QLED,electron injection is not sufficient for blue QLEDs due to a higher potential barrier at the quantum dot?QD?/ZnO interface.In this work,a lithium fluoride?LiF?interlayer is inserted between ZnO and the quantum dot layer to improve the efficiency and stability of blue QLEDs.The LiF interfacial layer facilitates electron injection into QDs through the electron tunneling effect and suppresses the exciton quenching at the QD/ZnO interface.As a result,the blue QLED devices show the maximum external quantum efficiency and current efficiency of 9.8%and 7.9 cd A^-1,respectively,which are 1.45 times and 1.39 times,respectively,higher than those of control devices.The operational lifetime of devices is also improved by two times.this thesis indicates that interface engineering is an effective method for high efficiency and stable blue QLEDs.Based on the above results,we try to use another method to solve the problem.in this thesis,we employ Mg doped ZnO?ZnMgO?as electron transport layer?ETL?in blue QLEDs,the conduction band of ZnMgO is higher than ZnO,therefore,it reduces the potential barrier at the QD/ETL interface,then electrons will inject into quantum dots effectively.meanwhile,it suppresses the exciton quenching at the QD/ETL interface.consequently,the blue QLED show the maximum external quantum efficiency and current efficiency of 9.4%and 8.4 cd A^-1,respectively,which have 81%and 83%enhancement,respectively,than those of control devices.The operational lifetime T50 of devices is 2.42 hours at a initial brightness of 670 cd m^-2,which is improved by nearly 1.6 times.this work indicate that ZnMgO is an excellent electron transport material for high efficiency and stable blue QLEDs.