Renqiang Yang, Hongbin Wu, Yong Cao
Oct 20, 2006
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Influential Citations
158
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Journal
Journal of the American Chemical Society
Abstract
Counterion exchange in cationic conjugated polyelectrolytes provides for a straightforward method to modulate the performance of these materials as the electron transport (injection) layer (ETL) in organic light emitting diodes. The bromide counterions of [(9,9-bis(6'-N,N,N-trimethylammonium)-hexyl)fluorene]bromide (PF-Br) can be easily replaced with trifluoromethylsulfonate (PF-CF3SO3), tetrakis(imidazolyl)borate (PF-BIm4) or tetrakis(3,5-trifluoromethylphenyl)borate (PF-BArF4) by a procedure that involves precipitation and washing. The performance of LEDs using MEH-PPV as the emissive layer, Al as the cathode, and the conjugated polyelectrolytes as the ETL varies in the order: PF-BIm4 > PF-CF3SO3 > PF-Br > PF-BArF4. In the case of PF-BIm4, the luminous efficiencies of the devices are similar to those of devices using Ba as the cathode. Thus, by properly choosing the counterion one can use higher work function metals that are more stable than lower work function metals without a substantial barrier to electron injection.