| Top-emitting organic light-emitting diodes(TOLEDs) are particularly suitable for active matrix displays due to their favorable merits, such as high efficiency, large aperture ratio and high pixel resolution. Recently, many efforts have been made to improve the performance of TOLEDs. Nevertheless, the structures of these high-performance TOLEDs are usually complex. What’s worse, the emission spectra change a lot over different viewing angles, which is a serious problem for display application. The thesis aims at applying ?nite-difference time-domain(FDTD) method in TOLEDs for researching and developing TOLEDs with high efficiency, low current ef?ciency roll-off, and hardly detectable spectrum shifts with viewing angles. Furthermore, by introducing ultrathin non-doped emissive layer(EML) and analyzing the influences different of EMLs on outcoupling efficiency of TOLEDs, we have successfully demonstrated TOLEDs with a simple structure can achieve high efficiency and low efficiency roll-off. Focusing on these aims, the thesis is organized as follows.Firstly, we have successfully applied FDTD method in TOLEDs for structure optimization, demonstrating good agreement with experimental data. A mixed host with both hole transporting and electron transporting materials is employed for the green phosphorescent OLED to avoid charge accumulation and broaden the recombination zone. The resulting TOLEDs exhibit ultra-high ef?ciencies, low current ef?ciency roll-off, and a highly saturated color, as well as hardly detectable spectrum shifts with viewing angles. In particular, a current ef?ciency of 127.0 cd/A at a luminance of 1000 cd/m~2 is obtained, and maintains to 116.3 cd/A at 10,000 cd/m~2.In order to simplify device structure, ultrathin non-doped EML has been employed in green phosphorescent TOLEDs to take full advantages of the cavity standing wave condition in a microcavity structure. Much higher out-coupling ef?ciency has been observed compared to conventional doped EML with relatively wide emission zone. A further investigation on dual ultrathin non-doped EMLs separated by a special bi-layer structure demonstrates better charge carrier balance and improved ef?ciency. The resulting device exhibits a high ef?ciency of 125.0 cd/A at a luminance of 1000 cd/m~2 and maintains to 110.9 cd/A at 10,000 cd/m~2. |
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