Two-layer OLED

FIGURE 3.7 Energy-level diagrams of (a) a single-layer OLED and (b) a two-layer OLED based on a p-type emitter and an ETM. (From Kulkarni, A.P., Tonzola, C.J., Babel, A., and Jenekhe, S.A., Chem. Mater., 16, 4556, 2004. With permission.)... 

Figure 7.5 shows a schematic example of the electroluminescent process in a typical two-layer OLED device architecture. When a voltage is applied to the device, five key processes must take place for light emission to occur from the device. 

Figure 6. Schematic illustration of organic light-emitting diode (OLED) operation (upper left) a single-layer OLED at zero bias, (upper right) a single-layer OLED at forward bias, and (bottom) a two-layer OLED at forward bias.

Fig. 11.6 The structure and schematic energy diagram of a two-layer OLED. With a suitable choice of the layer thicknesses, recombination occurs in the emission layer (EML) Alq3 in the neighbourhood of the HTL/Alq3 interface layer. Alq3 is simultaneously the electron transport...

ITO anode/hole-transporting layer (HTL)/emitting layer (EML)/metal cathode Chart 6.3 Structure of a two-layer OLED. 

Although PPPs and its derivatives reveal extraordinarily high thermal and oxidative stabilities, corresponding single-layer OLEDs exhibit only low electroluminescence efficiencies. Higher efficiencies have been achieved by preparing polymer blends or by virtue of two-layer OLED-constructions. External efficiencies up to 3% were determined for an ITO/PVK/poly(2-decyloxy-l,4-phenylene)/Ca — OLED [86,87]. 

Fig. 42 A phthaloqranine SAM as the hole injection layer in a two-layer OLED with M,M -bis(3-methylphenyl)-l,l -biphenyl-4,4 -diamine (TPD) as the hole transport layer and tris(8-hydroxyquinolinato)aluminium (Alqs) as the electron transport and emitting layer [219]...

Figure 13-4. Encigy level diagnim of a single-layer OLED, where the organic malerial is depicted as a fully depleted semiconductor. The valence band Ey corresponds to the HOMO and the conduction band Ec corresponds to the LUMO. Tile Fermi levels of the two metal electrodes are marked as Et-. Upon contact a built-in potential is established and needs to be compensated for, before the device will begin to operating.

FIGURE 7.1 A two-layer vapor-deposited OLED first demonstrated by Tang et al. [4], The diamine acts as the hole transporting layer, Alq3 acts as the electron transporting or emitting layer. The external quantum efficiency was 1%. 

Fig. 1.20. Schematic energy band diagram of a two-layer organic light emitting diode (OLED), in which tin-doped indium oxide (ITO) is used to inject holes into the highest occupied molecular orbital (HOMO) and a low work function metal to inject electrons into the lowest unoccupied molecular orbital (LUMO)...

Bacher et al. [15] reported on a series of triphenylene derivatives with one, two or three reactive acrylate units for crosslinking (Fig. 9.8(a)). No influence of the number of acrylate units on the degree of crosslinking was reported. Bi-layer OLEDs with the triphenylene as hole-transport agent and vapor-deposited A1Q3... 

Electroluminescent spectra for two-layer (Y/B), three-layer (R/G/B), and four-layer (R/Y/B/G) white OLEDs. (Reproduced from Spindler, J.R and Hatwar, T.K., SID Int. Symp. Dig. Tech. Papers, 38, 89,2007. With permission.)... 

As was pointed out earlier, blue is often the weakest link in the white OLED structure and needs improvement both in efficiency and stability. A novel architecture has been developed to obtain a stable blue color by using a similar format to the high-stability white devices. To this end, it was found that a stable blue emission could be obtained by using a "white" structure if the blue emission is decoupled from the yellow emission by the introduction of a thin, nonemitting buffer layer between these two layers. This nonemitting buffer layer consists of a HTM (such as NPB) and an ETM (such as EK-BH121). Figure 14.15 shows the stabilized blue device structure. The... 

Silyldisubstituted PPV [poly(2,5-bis(trimethylsilyl)-1,4-phenylenevinylene)] (BTMS-PPV, Fig. 38) was prepared via two different precursor polymers, a water-soluble sulfonium and an organic soluble thiophenoxy precursor polymer [160]. In a single layer OLED device fabricated with BTMS-PPV (from the thiophenoxy precursor) as emitter showed a emission peak at about 545 nm, although with a turn-on voltage of 20 V and an external quantum efficiency of... 

The materials described in the preceding section may be combined in an OLED de vice in a variety of different geometries and compositions. The simplest of these is a single oiganic layer sandwiched between two electrodes. In contrast to the convention used in surface science, it is customary to list the layers in the order of deposition. Thus, anode/organic/cathodc (for example, ITO/PPV/A1) implies that the anode (ITO) is deposited first on the (presumably transparent) substrate. 

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