Light-emitting diode of fully conjugated heterocyclic aromatic rigid-rod polymer doped with multi-wall carbon nanotube

Poly- p -phenylenebenzobisoxazole (PBO) and carbon nanotube (CNT) contain fully conjugated rodlike backbone entailing excellent mechanical properties, thermo-oxidative and solvent resistance. Rigid-rod PBO is commonly processed by dissolved in methanesulfonic acid or Lewis acid. A CNT of 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, all PBO/ M WNT composite films retained same but enhanced UV-Vis absorption peaks showing that M WNT and PBO do not have overlapping electron orbitals affecting their energy gaps. The composite films were excited at 325 nm using a He-Cd laser for photoluminescence (PL) response. All PL spectra had maximum wavelength peak at 540 nm indicative of yellow-green light emission. In the case of light emitting diodes, M WNT doped PBO would decrease threshold voltage for about 2 V and increase device emission current up two orders of magnitude than those without M WNT. This required a larger bias voltage leading to a shorter device lifetime.