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Study About The Structure Improvement And The Performance Enhancement Of Blue Organic Light-Emitting Devices

Posted on:2014-06-08Degree:MasterType:Thesis
Country:ChinaCandidate:J J BaiFull Text:PDF
GTID:2268330398490245Subject:Condensed matter physics
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In recent years, organic light-emitting diodes (OLEDs) have attracted considerable attention from some corporations of state-light and plat-panel display due to theirs excellent advantages of high brightness, wide viewing angle, low power consumption, panel display, etc. No matter whether they are applied to display or illumination, it is very important to demonstrate the blue devices with good electroluminescence (EL) performances, simple fabrication process and longer device lifetime. This paper mainly concerns the electrical and optical performances enhancements such as:luminance, current efficiency and power efficiency based on blue fluorescent OLEDs. We have designed different structures of devices, studied and discussed the effective injection, transport and recombination of carriers in the emitting layer. Simultaneously, the effect of broade carriers’ reconbination zone and effective excitions restricted at the interface on EL performances based on the light-emitting process and some basic mechanisms are researched.1. Inserting the carrier control layer (CCL) into the single emitting layer (EML) would depress the injection and transport ability of holes. Firstly, DPVBi and DSA-ph are used as EML and CCL, respectively. It is found that the luminance and current efficiency of the devices with CCL is improved compared with that of the control device. However, CIE coordinates of all devices with CCL are red-shifting. Consequently, Alq3with a good electron transporting property was inserted into DNCA which is prone to hole transporting as CCL because there is no possibility of happening energy transfer between them. The optimal device structure is achieved by adjusting the position of the CCL inserted into the EML. The maximal current efficiency of the optimal device is5.89cd/A, which is2.19times higher than2.68cd/A of the control device (CD). Besides, the device exhibits the good color stability and its maximal luminance is19,660cd/m2.2. Analyzing the mechanism of electron injection and transporting by employing the n-type doping technology and multiple repeat cells in electron transporting layer (ETL). Firstly, the EL performances of devices with multiple repeat cells are enhanced compared with that of the conventional device without electron injection layer. Meanwhile, given that the thickness of CS2CO3closed to cathode has an influence on the reducing of electron injection barrier. In order to eliminate this influence, the thickness of CS2CO3closed to cathode is fixed, and the structure of multiple repeat cells is still employed in ETL. Meanwhile, the device performances are compared with that of device with n-type doping. It is found that the device shows the best performance when the number of repeat cells is one. The maximal brightness and current efficiency of the optimal device with repeat cells are9,077cd/m2and3.59cd/A, which have the same effect with n-type doping device whose corresponding values are11,170cd/m2and3.98cd/A.3. Combing the composite hole transporting layer and novel homogeneous double emitting layers in one device to adjust the carriers’ balance and excitions recombination zone. Consequently, the concept of c-HTL has been raised and its thickness is optimized in order to depress the hole mobility. The device with20nm of c-HTL shows the good carriers’ balance as a result of a relatively obvious rectifying characteristic. In order to avoid this problem, we have employed the structure of homogeneous DELs and adjusted the doping concentration of guest in ADN. The energy transfer is conducted completely and the device shows the best EL performances when the doping concentration of DSA-ph is6wt%. The optimal device reveals that the current efficiency is enhanced by75.03%at a current density of4.91mA/cm2, while current density is reduced by44.19%under the same luminance of25,780cd/m2compared with those of the conventional device. Simultaneously, the efficiency roll-off of the optimal device is reduced by62.44%compared to that of single-emissive-layered device at the driving voltage of5-10V.
Keywords/Search Tags:Blue organic light-emitting diodes (OLEDs), carrier control layer, multiple repeatcells, composite hole transporting layer, homogeneous
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