AC-DRIVEN LEDs

More recent developments in CP-based LEDs have seen more specialized applications, in particular devices operated by AC rather than DC drive voltages, and those emitting polarized light or having claimed submicron structures (discussed in the subsequent sections). 

CPs used in AC-driven LEDs, by the MacDiannid/Epstein groups [771], 

Schematic of SCALE device. After Reference [770], reproduced with permission. 

SCALE devices have symmetric config[uration 

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The relatively new CP structures embodied in poly(pyridine) and poly(pyridyl vinylene), used especially for AC-driven LEDs by the Epstein group ... 

Another approach towards tailoring of color is of course discovery of entirely new, electroluminescent CPs which emit at different wavelengths. Such an approach has been demonstrated in more recent work by the Epstein group at Ohio State University [770, 771]. Thus, they have found that pOly(p-pyridine) emits blue light and poly(p-pyridyl vinylene) emits orange light. Many of these materials and devices are discussed in the section on AC-driven LEDs below. 

Carry out the exercise of Problem 1. for a) a two-CP-layer LED, with one being the emitter and one a hole-injector give likely candidate CPs usable, b) a three-layer LED which may be AC driven. 

Figure 166 The time dependence of device luminance (a) for a three layer LED (b) operated at a field ca. lMV/cm as driven by the direct current (DC), alternating current (AC) and pulsed current (PC) modes. The frequency of the pulsed excitation was 1kHz for both the AC and DC modes. After Ref. 586. Copyright 2000 Jpn. JAP, with permission.

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