Study On The Improvement Of Efficiency And Contrast In Organic Light-emitting Devices

Display technologies using organic light-emitting diodes (OLEDs) are capturing growing attention these days. A typical OLED device can be small molecule or polymer based and consists of two electrodes, a hole-transport layer, an electron transport layer, and an emissive layer. The front electrode is a transparent conducting material, such as a combination of indium-tin-oxide (ITO) . The rear counter electrode must possess good electron injecting properties,thus have a low work function.OLEDS can be promoted with better charge injection as well as the balance of the opposite charge carriers.In this paper, when cathode Al was modified by poly(ethylene oxide) PEO/LiF and(Poly(N-vinylcarbazole)) PVK was inserted between anode and emitting layer, the threshold, the luminescence intensity, efficiency and stability of device were improved significantly. Experiment results show that improvement of the device performance is caused by the introduction PEO and PVK, For opposite charge carriers Trends to balance. In addition, in high ambient illumination, the reflective back electrode reflects the incident ambient light, resulting in a decrease in contrast of the displayed image. Circular polarizers that can be bonded to the outside surface of the display have been widely used to reduce the glare from ambient illumination. However, their use adds extra cost, and a polarizer bonded to a display is not an integral part of an OLED structure. Other approaches to increase display contrast that have recently been proposed include the incorporation of sputter-deposited inorganic optical interference films in the OLEDs or the use of electron beam-evaporated layers of light absorbing inorganic materials. However, the involved aggressive deposition techniques and stringent deposition requirements continue to undermine their suitability for OLEDs.In this work, light-absorbing layer, made of multiple layers of metals and organic materials, was utilized to reduce reflectance of cathode.