Polythiophenes quantum yields

Bolognesi and co-workers prepared [3-((o-methoxy)alkylthiophene)s lOa-c by Ni-initiated polymerization of 2,5-diiodothiophenes [34, 35, 36]. A small red shift in EL of polymer 10c, compared with polymer 9e (from 1.8 to 1.95 eV), was presented as an indication of a lower bandgap in the former [31, 34], although it could be the result of asymmetry of the wide emission band (comparison with poly(3-decylthiophene) (P3DT) 9d revealed a smaller blue shift of 0.05 eV [37]. Polymers 10a,b showed high (for polythiophenes) PL quantum yields in solution (38-45 % in THE) that decreased, however, in the films [36], A general... 

In forward bias, tunneling injection diodes exhibit relatively high efficiency electroluminescence which is promising for flat panel and/or flexible, large area display applications. In reverse bias, on the other hand, the devices exhibit a strong photoresponse with a quantum yield >20% (electrons/phonon at —10 V reverse biaa) [135,136]. Devices based on derivatives of polythiophene exhibit an even better photoresponse (80% electrons/phonon at -15 V), competitive with UV sensitized Si photodiodes (Figure 8.46) [135,136]. 

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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