Energy-level diagram, 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 4.5 Schematic energy level diagram of a generalised monolayer organic light-emitting diode (OLED). ...

Figure 11.21 Proposed energy level diagram of the HOMO and LUMO energies of the materials used to prepare OLEDs based on Tb(tb-PMP)3(TPPO) [60]. (Reproduced with permission from S. Capecchi et al., High-efficiency organic electroluminescent devices using an organoterbium emitter, Advanced Materials, 2000, 12, 1591-1594. Wiley-VCH Verlag GmbH Co. KGaA.)...

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

Figure 22 (a) Cross-sectional schematic diagrams of OLED structures (side view) (top) single layer, (middle) single heterostructure and (bottom) double heterostructure. ITO = indium-tin-oxide. The electrodes are typically 1,000-2,000 A thick. The sum of the organic layer thicknesses are <2,000 A. (b) Ideal energy level diagrams for each of the device structures. 

Figure 23 Energy level diagrams for OLED materials. Only the frontier orbitals are considered, (a) Transition from the molecular orbital energies to narrow bands in the solid state to the parallelogram image of the HOMO and LUMO energies are shown, (b) The effect of an applied bias on the energy levels (left). The red arrows illustrate carrier injection via tunneling (tu), thermionic emission (te), or midgap states (mg). The midgap states are shown in blue.

Figure 30 Energy level diagrams for double heterostruoture OLED with a hole-blocking layer. The approximate energies of the HOMO and LUMO levels for lr(ppy)3 and ROEP are shown In green and purple, respectively.

Device structure of D-EML p-i-n OLED and the proposed energy level diagram. Anode and cathode are ITO and Al. (From Fie, G. et al., Appl. Phys. Lett., 85,3911,2004. With permission.)... 

Device structure and energy level diagram of green phosphorescent OLED with mixed EML and TBADN Bphen ETL. HOMO energies were obtained as IPs by UPS spectroscopy or as electrochemical oxidation potentials by cyclic voltammetry. LUMO values were estimated from solution-determined redox data. Unless otherwise noted, redox processes were reversible. No reduction was observed for TCTA within solvent window, LUMO of TCTA is significantly higher than the shown value. Irreversible reduction was observed for Bphen LUMO may be up to 0.3 eV higher. ... 

Holes and electrons are injected from the ITO electrode (anode) and the metal electrode (cathode), respectively. The energy level diagram under forward bias is shown in Fig. 6.5. More sophisticated OLEDs possess multilayer structures as shown in Fig. 6.4 b. 

Fig. 6.1 Energy level diagram of an OLED showing the HOMO and LUMO energy levels, EgoMo and Eiumo, of an organic thin film sandwiched between an anode and a cathode of work functions WFa oi(, and WFcathode respectively. The levels are tilted because of the built-in field. A photon of energy is emitted from the OLED...

Fig. 7.2 Energy level diagram and materials used in an efficient green phosphorescent OLED [8]...

Figure 4.33. (a) Sketch of the basic construction of an OLED. (b) Schematic diagram showing the energy-level alignment for the OLED ITO/CuPc/NPB/Alqs/Mg. Adapted from Lee et al, 1999. 

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