OLEDs/PLEDs

Figure 4.45. Multilayered structure of OLEDs/PLEDs. Also shown are the relative energy levels for individual layers hght is emitted as a result of the radiative recombination of electron-hole pairs.

Figure 4.46. Molecular structures of commonly used OLED/PLED materials. Shown are (a) Alq3 (tris(quinoxalinato)Al (III)) used as an electron-transport material (b) DIQA (diisoamylquinacridone) used as an emissive dopant (c) BCP (2,9-dimethyl-4,7-diphenyl-l,10-phenanthroline) used as an exciton/ hole blocking agent (d) NPB (l,4-bis(l-napthylphenyl amino)biphenyl) (e) PFO (9,9-dioctylfluorene) used as an emissive polymer in PLEDs (f) PEDOT-PSS (poly-3,4-ethylenedioxythiophene-polystyrene sulfonate) used as a hole transport material in PLEDs.

Accurate Measurement of OLED/PLED Device Parameters 155... 

A prime concern of the OLED/PLED community is the level of uncertainty and inconsistency of results found in published scientific literature. Here, we summarize an accurate method for measurement of OLED/PLED optical properties. 

Because the major application of OLEDs/PLEDs is for displays, the response of the human eye, described by the photopic luminosity function [15], must be taken into account. The photopic luminosity function is shown in Fig. 4.4. By using the photopic luminosity function, the radiance (watts/(sr m2)) is converted into the luminance (candela/m2, cd/m2 or lumen/(sr m2)). Therefore, photometry is used to measure the forward viewing luminance at the surface of an OLED/PLED. 

To measure the luminous intensity one must first choose a reference direction for the measurements, and one must then determine the solid angle to be used in the measurement. For display applications, the reference direction should be chosen as the forward viewing direction (along the direction perpendicular to the surface of the OLED/PLED). The luminous intensity is defined as the emission in cd/m2 from the emitting surface. 

An accurate and convenient configuration for measuring luminous efficiency from OLEDs/PLEDs is shown in Fig. 4.5. Because the luminous efficiency strongly depends on the OLED/PLED emission spectrum (even for constant quantum efficiency), an eye-sensitivity filter is mounted directly onto the surface of the calibrated photodiode (see Fig. 4.4) [15],... 

Once the luminance, L (cd/m2), is accurately measured the luminous efficiency, LE (cd/A), luminous power efficiency, PE (lm/W) and external quantum efficiency, 7ext (the ratio of the number of photons emitted by the OLED/PLED into the viewing direction of the number of electrons injected) can be determined using the following expressions [20] ... 

Note that, as indicated by Optronic Laboratories, the response of a diffuser/fiber combination is far from uniform or ideal [21], Not only does the fiber/diffuser combination fail to provide the correct measurement area, but also the nonuniform spatial response makes the result highly sensitive to alignment. Therefore, the fiber/diffuser combination should be avoided if the OLED/PLED intensity is to be correctly measured. 

Although for mobile applications new display principles based on organic hght emitting diodes (OLED/PLEDs) are close to market introduction, the market share of LCDs in telephone displays is still 100%. The demands on... 

When 3,4-ethylenedioxythiophene (EDOT) is chemically polymerized in the presence of polyacrylic acid (PAA) as a template, conducting nanowires can be assembled from smaller nanowires in a side-by-side manner and exhibit excellent conductivity [115]. The electronic properties of PTh have promoted a wide interest in the development of organic/polymer light-emitting diodes (OLEDs/PLEDs) and it is note worthy that the performance of these devices is dramatically enhanced by the... 

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