Prospects for Applications of PPV-Based LEDs

Recent encouraging results have been reported by Carter et al., who have obtained room temperature lifetimes in excess of 7000 h for encapsulated ITO/PPV/Ca devices at current densities of 60 mA/cm2.37 The polymer used was the PPV copolymer shown in Fig. 5.23, where the conjugation is interrupted by nonconjugated a -acetyloxy-/ -xylylene units. The efficiency of these devices was typically 0.02 lm/W. Devices operating at 80° C had lifetimes in excess of 1100 h. Carter et al., also reported devices based on the same emissive polymer giving efficiencies between 0.5 and 2 lm/W. These devices used a layer of conducting polymer (polyethylenedioxythiophene/polystyrene sulfonate) between the ITO and the PPV, and a sputtered aluminum/lithium alloy as the cathode. The devices 

FIGURE 5.23. PPV copolymer with high luminescence efficiency. 

Polymer Morphology and Device Performance in Polymer Electronics 

FIGURE 6.1. Two examples of different emission spectra of MEH-PPV thin films. The emission maximum of curve a appears at 580 nm, and that of while curve b appears at 630 nm. 

the metal/polymer interfaces, and the energy barriers for charge injection (Sec. 3.B), the device turn-on voltage (Sec. 3.C), the emission spectrum (Sec. 

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