Optical Design Of High Performance Tandem Organic Light-emitting Device

Organic light emitting-doide (OLED), which is considered as the next generationflat panel display technology, exhibits many particular merits such as self-emission,solid-state, light weight and can be flexible.After more than two decades ofdevelopment, OLED technology begins to bring us more and more amazing products.However, there are still many difficulties we need to overcome before this technologyrelease the full potential.Among them, the OLED performance is still the key to limit itsdevelopment. Tandem structure provides the researchers an optional way to solve thisproblem. Compared with traditional OLED, tandem OLED can achieve higher currentefficiency and luminance as well as longer lifetime. Therefore, the design of a highperformance tandem device causes more and more attentions.Since the micro-cavity effect plays a key role in determine the optical property oftandem devices, we focused our study on this effect to find the way of designing highperformance OLEDs. We systematically studied and simulated the influence ofmicro-cavity effect on tandem OLED’s optical characteristics, such as output intensity,color rendering index and angular emission properties. Based on these results, weproposed an image processing method to design the high performance tandem devices.The main research achievements involved in this thesis are as follows:(1) Based on the fact that the emission spectra of tandem devices can be treated assuperposition of each emission spectrum of monocolor units, we proposed a simplemethod to calculate the tandem OLED emission spectra. Using the calculated spectra,the output intensity, color rendering index and angular emission property can beobtained.(2) To obtain the high performance tandem blue OLED. We firstly optimized theemission property of single-stacked blue OLED using the Intermix structure. Theefficiency of blue OLED can reach10.5cd/A and8.7lm/W. Based on this structure, atandem blue OLED is fabricated with the help of optical simulation. The currentefficiency of tandem blue OLED is as high as22cd/A.(3) To obtain high performance complementary color tandem white OLED. Wesystematically studied the micro-cavity effects on the influence of devicesperformance. The output intensity, color rendering index and angular emission property are presented based on optical simulation. Using an image processingmethod, we successfully obtained the optimized layer thickness which meet ourrequirements. The fabricated tandem White OLED is only140nm and shows a quitlow driving voltage performance. The driving voltages for1,100,1000and10000cd/m2are only5.2,6,6.8and8.7V, separately. Meanwhile, the tandem devices alsoshows a high efficiency (70.3d/Aand36.2lm/W) and good angular emission property.When the observation angular changing for0oto60o, the CIE coordinate is slightvaried from (0.344,0.428) to (0.337,0.419).(4) We also simulated and studied the optical properties of three-stackedRGB-OLED. Based on the simulation results, we used our image processing methodto obtained the optimized layer thickness where high performance devicecharacteristics can be realized. We successfully fabricated a160nm tandemRGB-OLED. The driving voltages at100cd/m2,1000cd/m2,10000cd/m2are10.6V,12.1V,14.5V, separately. The device also shows a good angular emission property,When the observation angular changing for0oto60o, the CIE coordinate is slightvaried from (0.3286,0.453) to (0.3108,0.417).