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Enhancement Of Electron Injection And Influence Of Fluorescent Dopants On Carrier Transporting Of OLED

Posted on:2016-05-17Degree:MasterType:Thesis
Country:ChinaCandidate:L W XinFull Text:PDF
GTID:2308330461488278Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
In recent years, people have paid a lot of attention to organic light-emitting devices(OLEDs), because their potential application for panel displays and solid-state illumination. In order to achieve efficient OLEDs, it is critical to enhance the carrier injection and keep the carriers in balance. In this work, we investigate that how to enhance electron injection and influence of trapping and scattering caused by fluorescent dopants in organic light-emitting devices with an organic homojunction.1. We investigate the electron injection effect of inserting a thin aluminum(Al) layer into cesium carbonate(Cs2CO3) injection layer. Two groups of organic light-emitting devices(OLEDs) were fabricated. We investigate the perpermance of the devices and find that inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.2. The performance of organic light-emitting devices(OLEDs) is improved by inserting Tetracyanoquinodimethane(TCNQ) electron buffer layer between 4,7-diphnenyl-1,10-phe-nanthroline(Bphen) electron transport layer and Li F/Al cathode. By optimizing the thickness of TCNQ layer, we find that the device with 6 nm TCNQ buffer layer achieves the best performance. The maximum luminance, current efficiency, power efficiency and half-lifetime of the device with 6 nm TCNQ buffer layer increase by 7.98%, 9%, 22%, and 13.6% respectively, compared to those of the device without TCNQ buffer layer. The improvement of the device performance can be attributed to that the insertion of TCNQ buffer layer can enhance the electron injection and operational stability of the devices.3. In this work, we report two fluorescent homojunction organic light-emitting devices with p-i-n structure based on a single ambipolar organic semiconductor, 4,4 ′-Bis(carbazol-9-yl)-biphenyl(CBP), as matrix organic materials. In these devices, CBP is doped with two different blue fluorescent dopants. Influence of trapping and scattering caused by fluorescent dopants on carrier transporting is investigated. We find that at the low voltage, low scattering strongly affect carrier transporting and deep trapping hardly affect carrier transporting, but at the high voltage, the situation is reversed. The experimental results are explained by Miller-Abrahams hopping model. Moreover, we study influence of trapping and scattering caused by fluorescent dopants on the electroluminescent performance of the two types of devices.
Keywords/Search Tags:OLED, electron injection, thin Al layer, trapping, scattering, carrier transport
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