Electroluminescence Emission of Fully Conjugated Heterocyclic Aromatic Rigid-rod Polymer Doped in \textit{Multi}-wall Carbon Nanotube

Carbon nanotube and poly-$p$-phenylenebenzobisoxazole (PBO) contain fully conjugated rodlike backbone entailing excellent optoelectric properties and solvent resistance. Rigid-rod polymer PBO is only soluble in methanesulfonic acid or Lewis acid. \textit{Multi}-wall carbon nanotube ($M$WNT) was dissolved in a Lewis acid solution of PBO for dispersion of nanotube, and then spun for thin film. $M$WNT concentration in the films was from zero up to 5 wt. {\%}. Compared to that of pure PBO film, composite films of $M$WNT doped PBO showed same UV-Vis absorption peaks which were enhanced with $M$WNT concentration but without overlapping electron orbitals to effect their energy gaps. All films were excited by He-Cd laser with excite wavelength of 325 nm for photoluminescence (PL) response. All PL spectra had maximum wavelength peak at 540 nm indicative of yellow-green light emission. For light emitting diodes, $M$WNT doped PBO would decrease threshold voltage for about 2 V. At 0.1 wt. {\%} of $M$WNT, the composite device emission current was increased up to two orders of magnitude than the PBO diodes without $M$WNT. Further increase of $M$WNT caused a successive decrease in electroluminescence emission intensity attributed to a quench effect form aggregation of $M$WNTs.