Polymer light emitting diodes and poly(di-n-octylfluorene) thin films as fabricated with a microfluidics applicator

H. Cheun, P. P. Rugheimer, B. J. Larson, P. Gopalan, M. G. Lagally, and M. J. Winokur.
Journal of Applied Physics 100, 073510 (2006).

A microfluidics applicator is used in the fabrication of a polyfluorene based polymer light emitting
diode (PLED). This procedure results in a single contiguous polymer trace and, as a consequence of
the high deposition speed, shows unusual characteristics in both the film morphology and polymer
microstructure. These aspects are studied using fluorescence microscopy, profilometry, and optical
absorption and emission spectroscopies. Room temperature analysis of the poly (di-n-octylfluorene)
indicates that the combination of high-speed deposition and rapid drying process traps the polymer
into a metastable conformational state. Optical spectroscopy at reduced temperature identifies
emission from at least two distinct conformational chromophores. At elevated temperature there is
an abrupt, irreversible transition to a more conventional structural form. Electroluminesence data
from PLED test devices are shown and this demonstrates some of the unique opportunities afforded
by this method of polymer film formation and device fabrication. Device operation is not

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