Investigation On The Performance Of CuIn S₂/ZnS Based Quantum Dot Light Emitting Diodes

Colloidal quantum dots?QDs?or semiconductor nanocrystals are much attractive for many optoelectronic applications because of their important advantages such as size-controllable emission wavelength tunability,narrow linewidth,and solution-processed fabrication.Its distinctive optical properties,such as its narrow bandwidth and tunable photoluminescence?PL?,have attracted much attention in the past three decades,especially in terms of the high color purity and wide color gamut of QDs in display.Since the colloidal quantum dot light-emitting diode?QLED?was first reported in 1994,various approaches have been taken to improve the performance of the device,including designing new device structures,developing new QDs and transport materials,and optimizing the carrier injection.Compared with the earlier use of a thick QD layer as the emitting layer and the electron transport layer?ETL?,the efficiency of the QLED has been greatly improved by using a single-layer ordered QD,which minimizes the resistance and makes excitons highly efficient limited to the light emitting layer.Higher QLED performance can be obtained by optimizing the thickness of the QD layer and purifying the QDs.As the continuous development of the technology,there is a growing demand for high quality display and solid-state lighting.The new inverted structure device,due to its simple preparation process,lower cost and stable structure,further promote the development of QLED.Although the performance of QLED has been significantly improved in recent years,most of the conventional devices use CdSe QDs as emitting materials,which can not be used in large-scale due to the heavy metal toxic element Cd.At the same time,there is still much space for the improvement in carrier injection,electron-hole recombination,and carrier balance in the device for commercialization.In this paper,we present the inverted QLED based on the non-toxic CuInS₂/ZnS quantum dot in detail and improve the performance of the device by adding the intermediate layers.To further analyze the improved mechanism and the carrier distribution in the device,we take the impedance spectroscopy and transient electroluminescence spectroscopy measurement.The main contents of this paper are as follows:1.The research progress and development trend of quantum dots and quantum dot light-emitting devices are introduced in detail.Based on the traditional Cd-based QDs,the CuInS₂/ZnS quantum dot,which is non-toxic,has been proposed as the emitting layer.By analyzing the current characteristics of the device,we find that the low efficiency of the device is mainly caused by the unbalanced carrier concentration,and then proposes a method to improve the performance of the device.The interlayer PEIE was introducing into the device to block the excessive electron injection in order to balance the electron and hole concentration and improve efficiency.2.To further investigate this optimization mechanism and carrier distribution in the device,it can be concluded that the addition of a modified layer not only reduces the electron injection to balance the carrier,but also reduces the QDs charging process caused by the major carrier through the impedance spectroscopy and transient electroluminescence spectra measurement.At the same time,the modified layer blocks the direct contact between the zinc oxide surface and the QDs,thereby reducing the quenching behavior of the surface defects on the quantum dots.