Polyfluorenes for device applications

This article mainly reviews the approaches that have been proposed to improve the device performance of polyfluorene (PF)-based polymer light-emitting diodes (PLEDs). Chemical modifications on main chains, side chains, and chain ends of PFs via the incorporation of charge-transport moieties can reduce the hole- and electron-injection barriers; while physical manipulation on main-chain structures of PFs, poly(9,9-di-n-octylfluorene) (PFO), after dipping in mixed solvent/non-solvent (tetrahydrofuran/methanol) can generate P-phase with extended conjugation length, leading to a promoted charge balance and stable pure blue emission. Hole- and electron-inject ion barriers can be effectively lowered by the insertion of hole-transport and electron-injection layers, respectively. The recent development of PFs with various emission colors, via physical blending or chemical modification, are presented for a comprehensive understanding of PI's for device applications. The deliberate choice of cathode material with work function matching the lowest unoccupied molecular orbital (LUMO) levels of PI's is another efficient method for increasing electron flux, and is also discussed in this review.