Phosphorescent OLED device layer structure

Current density as a function of voltage for green phosphorescent OLED devices with mixed EML and various ETL (see legend). For organic layer structures see Figure 14.45 captions. 

Nakayama et al. reported highly efficient and stable single-stack white phosphorescent OLEDs based on blue triplet emitter KMBD-342 described in Section 14.4.2.3. Yellow-green (YD-85) and red (RD-61) dopants used in the device were provided by Universal Display Corporation. The device layer structure was as follows Light outcoupling film ITO HIL HTL green EML red EML I blue EML HBL n-doped ETL A1. At 1000cd/m the performance... 

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]. 

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. 

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. 

Very efficient phosphorescent OLEDs with a D-EML and p- and n-doped charge-transporting layers have been demonstrated. Their device structure is presented in Figure 14.41. The hole-transporting part of the D-EML consists of 4,4 4"-tris(carbazolyl)-triphenylamine (TCTA) doped... 

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