Phosphorescent OLED device material structure

The organic salt of tetrabutylammonium tetrafluoroborate (BujNBF ) was further dissolved into the basic organic solution at an appropriate concentration. The thickness of the spin-coated organic layer was about 80 nm. Then, an A1 cathode layer (100 nm) was formed on the top of the organic layers via thermal deposition at a rate of 0.7 nm/ s under a base pressure of 2 x 1Q Torr. In this experiment, phosphorescent OLEDs were fabricated and comprared one with BU4NBF4 (0.0050 wt%) annealed electrically at V = +7 V (forward bias) at T = 65°C the other for reference with BU4NBF4 (0.0050 wt%) annealed electrically at V = +20 V (forward bias) at T = 25°C. It should be noted that, except for the emissive layer, the device structure of the reference device was identical to that of the sample device. The structures of the devices and materials used were identical. The devices were prepared in inert Ar gas environments this preparation included electrical and thermal treatments. 

This section covers the background information for OLED devices that applies to both fluorescent and phosphorescent devices. In addition, materials and architectures specific to fluorescent devices are discussed. Phosphorescent structures are described in Section 14.4. 

At the early stage of phosphorescent OLED development, red triplet devices often employed a conventional architecture— HTL, EML, and ETLs were placed between the electrodes. Additionally, a HBL was often inserted between the EML and the ETL. The general structure of a red phosphorescent OLED is shown in Figure 14.30. The device may also include a HIL and an exciton/electron-blocking layer (EBL) placed on the anode side of the EML. The effect of the blocking layers on device performance and criteria for material selection for the layers in triplet OLEDs will be discussed in Section 14.4.2.2. The structures of materials commonly used in red phosphorescent OLEDs are shown in Figure 14.31. 

Another example of a white phosphorescent OLED with triple-doped EML was demonstrated recently. The device architecture was similar to that described above however, the material structures used were not disclosed. At lOOOcd/m the white triplet OLED showed 251m/W, CRI index of 78, and CIEx,y of (0.39,0.44). At lOOcd/m, the device power efficacy reached 301m/W, and with outcoupling enhancement the total power efficacy increased to 511m/W. 

In the vapor-deposited OLED community, a number of approaches have been employed to produce white light emission. White OLEDs have been demonstrated based on multilayer structures, e.g., stacked backlights [153,168], multidoping of single-layer structures [145], phosphorescent monomer-excimer emission layers [169] and on doping of phosphorescent materials into separate bands within the emission zone, called a tri-junction [170]. The trijunction device has produced the highest white OLED efficiency of 16% external quantum efficiency demonstrated thus far [171]. 

---