Facile brush-coated β-phase poly(9,9-dioctylfluorene) films for efficient and stable pure-blue polymer light-emitting diodes

β-Phase poly(9,9-dioctylfluorene) (PFO) films have been constructed in one step by direct brush-coating PFO solution onto substrates. The alignment of PFO chains was manipulated under directional stress, resulting in coplanar orientation of adjacent fluorene units. Both additional absorption peak and red-shifted photoluminescence (PL) spectra suggest the formation of β-phase for the brush-coated PFO films. β-Phase PFO device shows pure-blue emission with corresponding CIE coordinates of (0.170, 0.112), achieving a high current efficiency of 3.37 cd/A, which is twice to that of the device with spin-coated amorphous-phase PFO film. In addition, the β-phase devices show much more stable EL spectra as compared with those of the amorphous-phase devices. The results suggest that brush-coating can be used as a simple and efficient methodology to orient the polymer semiconductor films for applications in constructing high-performance optoelectronic devices.