Study Charge Balance Mechanism Of Organic Light Emitting Diodes

Organic light-emitting diodes(OLEDs) have already become a hot topic inemerging flat-panel display products at home and abroad due to their advantages suchas high brightness, wide angle, high efficiency, can produce large size and flexurepanels, simple fabricated process. The most important factor influence the OLEDcomponents efficiency is the recombination rate of electrons and holes, or the balance ofelectrons and holes in light emitting layer. Generally, the number of holes is more thanelectrons normal in light emitting layer, charge imbalance lead to low device efficiency.Therefore, we can get high device preference with improve the charge balance, which inorder to satisfy the demands of practical application. At present, researchers have foundmany effective methods to improve charge balance, add charge injection layer, improvethe charge transfer materials and device structure. This thesis mainly talk aboutimproving the charge injection to improve the device performance.Firstly, we systematically investigate the fluorescent and phosphorescent p-i-nOLED with well controllable compound doping, for both the p-type doping and n-typedoping can effectively reduce the operation voltage. No matter it is bulk doping orinterfacial doping, the doping configuration is demonstrated to have a great impact oncharge balance. Which n-type doping is in favor of hole and electron balance, it willmultiply the device efficiency. In contrast, p-type doping enhances hole and electronimbalance, it will compromise the device efficiency. It is therefore significant tomodulatethe p-doping and n-doping for optimizing hole and electron balance, and getmaximizing power efficiency.Moreover, by changing the electron modified layer in inverted OLED to investigate charge balance. Using a facile solution-processed ultra-thin alumina oxidefilm as an electron-injection layer can lower the work function of ITO, which canreduce the electron injection barrier in order to improve charge balance. In addition, wecan also increase electron injection by evaporating a thin alumina on ITO, it enhancesthe charge recombination rate then get high efficiency of device. In summary, and thesetwo electron modified layer with different preparation methods all can obviouslyimprove charge balance in inverted device, which obtain better device performance thanconventional device.The research work of this thesis confirms optimize the charge balance in organiclight emitting device can improve the device efficiency, improving charge balance is animportant methods to get high efficiency and low voltage device proformance.