Anionic triphenylamine- and fluorene-based conjugated polyelectrolyte as a hole-transporting material for polymer light-emitting diodes

BACKGROUND: Hole-transport layers (HTLs) play a crucial role in multilayer polymeric light-emitting diodes (PLEDs) for the achievement of satisfactory device performance. During the fabrication of multilayer PLEDs via solution processing, the fabricated HTLs encounter the risk of erosion during the film-forming process of subsequent emitting layers (EMLs). In contrast to the widely investigated crosslinkable HTLs, much less attention has been paid to the preparation of polar-solvent-soluble HTLs, which is a straightforward solution to overcome the interfacial mixing between HTLs and EMLs during solution processing. RESULTS: Alternating triphenylamine- and fluorene-based anionic copolymer poly[9,9-bis(4'-sulfonatobutyl)fluorene-alt-N-(p-trifluoromethyl)phenyl-4,4'-diphenylamine]sodium salt (PFT-CF3) was synthesized via a palladium-catalyzed Suzuki coupling reaction. This polyelectrolyte is soluble only in polar solvents such as methanol, dimethylformamide and dimethylsulfoxide rather than in non-polar solvents such as toluene, chloroform and xylene. The relatively high HOMO (-5.22 eV) and LUMO (-2.26 eV) levels of this polymer endow it simultaneously with good hole-transporting and electron-blocking capabilities. The performance of red-, green- and blue-emitting devices utilizing this polyelectrolyte as HTL was investigated. CONCLUSION: The anionic conjugated polyelectrolyte based on triphenylamine and fluorene, PFT-CF3, can serve as a promising hole-transporting/electron-blocking layer in multilayer PLEDs. (C) 2009 Society of Chemical Industry