Large counter cation cyclodextrin-threaded conjugated polyelectrolytes for light-emitting devices: Enhanced efficiency by complexation with ion transporting polymers
Gianluca Latini, Gustaf Winroth, Sergio Brovelli, Shane O. McDonnell, Harry L. Anderson, Jeffrey M. Mativetsky, Paolo Samorì, Franco Cacialli, (2012)
The photophysics and electroluminescence of thin films of unthreaded and cyclodextrin encapsulated poly(4,4'-diphenylenevinylene) with potassium counter cations, blended with poly(ethylene oxide), PEO, are investigated as a function of the PEO concentration. We show that three main factors contribute to increasing the photoluminescence (PL) quantum efficiency as a result of suppressed intermolecular interactions, namely: the high degree of encapsulation of the polyrotaxanes, the relatively large counter-cation (e.g., compared to lithium) and the complexation of the rotaxanes with PEO. By facilitating cationic transport to the negative electrodes, PEO also leads to devices with enhanced electron injection and improved charge balance, whose operation therefore resembles that of “virtually unipolar” light-emitting electrochemical cells. This effect, together with the enhanced PL efficiency, leads to higher electroluminescence efficiency for both polyrotaxanes and unthreaded polymers, upon addition of the PEO. We show that the concurrent exploitation of the various strategies above lead to an overall electroluminescence efficiency that is approximately twice the value previously reported for Li-based poly(4,4' diphenylenevinylene). A blue-shift of the electroluminescence spectrum during the devices turn-on is also reported and analyzed in terms of interference and doping effects.
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