Carrier Recombination Photoluminescence and Electroluminescence

The progress in the PLEDs stimulated researchers into further efforts to apply a variety of potentially electroluminescent materials including the polythiophenes to this promising class of electronic devices [130, 131, 133]. As mentioned in section 2.2.2, the thermochromic behavior of PATs is a consequence of the main-chain conformational change. The coplanarity of the thiophene rings and deviation from 

The applications of the soluble polythiophene derivatives to the PLED are advantageous in that their polymer blends or composites can be easily formed [147]. Berggren et al. [126] have recently reported that these polymer blends (e.g. a mixture of different kinds of polythiophene derivatives) exhibit voltage controlled colors in electroluminescence. This effect was explained by the assumption that a number of nano-PLEDs of 50-200 nm in size yielded by micro phase separation are coupled parallel and operate in a specific voltage range depending upon the polymer species [126,130,131]. In addition, these nano-PLEDs dispersed in an insulator matrix such as poly(methyl methacrylate) display white hght emission with quantum efficiency ofO.4-0.6% [133]. 

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