Highly efficient polarized polymer light-emitting diodes utilizing oriented films of beta-phase poly(9,9-dioctylfluorene)

Uniaxially oriented films of beta-phase poly(9,9-dioctylfluorene) (PFO) were realized by a friction-transfer technique followed by thermal annealing and vapor treatments. Absorption and photoluminescence (PL) spectra show the characteristics of beta-phase: an additional absorption peak at 433 nm and redshifted PL peaks compared with those of the usual nematic (N) phase. We fabricated polarized polymer light-emitting diodes utilizing oriented films of beta-phase PFO. Highly polarized beta-phase emission with an integrated polarization ratio of 51 was observed from the devices. The efficiency of the devices based on beta-phase reached 2.0 cd/A, which is two times higher than that based on N-phase.