The Star Six Phenylfluorone Compounds Electroluminescent Properties

In recent years, the flat-panel display industry has grown tremendously due mostly to the success of liquid-crystal displays (LCD) and Plasma Display Panel (PDP). However, during this period, the technology of organic light-emitting diodes (OLEDs) has advanced so that it now can compete directly with LCD for high information content display applications. OLEDs have many advantages over LCD including a wide-viewing angle (>170°), faster data display, lightweight, flexibility, and power efficiency. However, the morphological instability of organic electroluminescent materials is one of the major problems in device applications. Star-shaped molecules have been proven to overcome this problem. In this thesis, multilayer OLED devices with optimized optical and electronic properties were fabricated with a star-shaped hexafluorenylbenzene 1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEt-hFLYPh) which has six arms star shaped fluorene structure.1. First, the characteristics of OLED, including the structures, advantages and disadvantages, and the development of OLED are introduced. Moreover, relevant principles about OLED are also discussed.2. Double-layer and triple-layer OLEDs were fabricated using HKEthFLYPh as an energy transfer layer, N,N′-bis-(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as a hole-transport layer (HTL) and blue emissive layer (EML), and tris(8-hydroxyquinoline)aluminum (Alq3) as an electron-transport layer (ETL) and green light-emitting layer, respectively. Bright white light was obtained with a triple-layer device structure of indium-tin-oxide (ITO)/NPB (50 nm)/HKEthFLYPh (10 nm)/Alq3 (40 nm)/Mg : Ag (200 nm). A maximum luminance of 8523 cd/m2 at 15 V and a power efficiency of 1.0 lm/W at 5.5 V were achieved. The Commissions Internationale de L'Eclairage (CIE) coordinates of the device were (0.29, 0.34) at 9V, which located in white light region. With increasing film thickness of HKEthFLYPh, light emission intensity from NPB increases relatively to that of Alq3. Meanwhile, HKEthFLYPh played the role as a hole blocking layer (HBL).3. To achieve white emission, the multisource evaporation process is usually used. However, with the coevaporation process it is difficult to control the deposition rate and dopant concentration. We described nondoped white organic EL devices based on the 5,6,11,12-tetraphenylnaphtacene (rubrene) ultrathin layer. WOLEDs were fabricated with an ITO/NPB (d nm)/HKEthFLYPh (10 nm)/NPB (50-d nm)/rubren (0.1 nm)/Alq3 (50 nm)/Mg : Ag (200 nm) structure. White light emission was achieved by combining blue and yellow emissions emitted from NPB and ultrathin rubrene layer, respectively. Fairly pure white light with CIE coordinates of (0.32, 0.33) was achieved when d was 50, and it exhibited more stable emission characteristic than other devices which with different ultrathin rubrene thickness. The device shows maximum luminance of 2182 cd/m2 at voltage of 15 V.4. The electroluminescence (EL) of the device ITO/HKEthFLYPh/BCP (20 nm)/Alq3 (30 nm)/Mg : Ag (200 nm) maximizes at 600 nm without the emission of HKEthFLYPh. So we conclude that the peaks at 600 nm may originate from the emission of electroplex. White emission obtained with the structure of ITO/HKEthFLYPh : NPB (4 : 1)/BCP (20 nm)/Alq3 (30 nm)/Mg : Ag (nm) because the electroplex emission is a red-shifted broad band in the EL spectra, and the relative emission of electroplex increased with enhanced electric field.