Functionalization Of High-Purified Few-walled Carbon Nanotubes And Their Opt-Electrical Applications

The development of nano-optoelectronic strongly relies on the discovery and exploration of new functional opto-electrical nanocomposites as a vital component of active layer. Since the discovery, carbon nanotubes (CNTs) were widely regarded as an ideal candidate to the building block of a series of high-response and low-cost opto-electronics such as optical switch, photodetecotor and photovoltaic devices due to favorable electron transport along with one-dimension tube-structure arising from highÏ€-conjugated system. Therefore, the researches on the opto-electrical properties of functional CNTs are fundamentally significant to actualize the applicable potential. In this thesis, we systematically focused on a profitable route from materials to application, and that is the synthesis, purification, functionalization and photoconversion devices based on single-walled carbon nanotubes (SWNT) and few-walled carbon nanotubes (FWNT). Results illustrated the relationship between opto-electical properties and devices, which are experimentally and theoretically important to potential applications.Highly purified FWNT was processed by room temperature purification in 30 wt % H2O₂ for 1 week with the yield up to 10 %. Raman spectra and TGA characterization indicated that H₂O₂ purification selectively oxidized carbonaceous nano-particles without the damage of the structure of FWNT. A new versatile and simple way of SWNT and FWNT decorated by Palladium nanoparticles (Pd NPs) was presented. Optimal decoration was achieved with a large amount of sphere-shape Pd NPs on the sidewall when weight ratio of CNTs and Na₂PdCl₄ is 1:4. Compared with original CNTs film, the conductivity of SWNT/Pd-NPs and FWNT/Pd-NPs film were enhanced up to 2 fold and 5 fold. Raman spectra showed that Pd NPs tended to be deposited on metallic SWNT. Organic conjugated molecule of N,N'1'-methyl- pyrene-3,4,9,10-perylene diimide (PDI-PY) was synthesized by covalent N-substitution. PDI-PY/SWNT and PDI-PY/FWNT nanocomposites with high and board absorption spectra were prepared byÏ€-electron stacking. Raman spectra indicated that metallic and semiconducting enriched SWNT were selectively separated due to different solubility in organic solvents after the functionalization.Organic photovoltaic devices (OPD) using high conductive transparent few-walled carbon nanotubes (FWNT) electrode was fabricated. Maximum efficiency of OPD up to 0.61 % with the structure of FWNT (transparency, T=70 %, sheet resistance, Rs = 86Ω/â–¡)/ poly(3-hexylthiophene) : [6-6]phenyl-C61-butyric acid methyl ester /Al demonstrated a promising alternative of ITO (0.68 %) with almost identical operation. The performance improvement resulted from the optimal balance between sheet resistance and transparency with three-dimensional network interface between nanotubes and polymers. A series of photoresponsive azobenzene chromophore-CNTs nanocomposites with different push-pull electronic groups (SWNT-AZO-NO₂,FWNT-chain-AZO,MWNT-AZO-NH₂) were synthesized via covalent amide reaction. The electronic interaction between azobenzene moiety and CNTs resulted in the red- and blue-shifts in absorption spectra of SWNT-AZO-NO₂ and MWNT-AZO-NH₂. Compared with SWNT-AZO-NO₂ and MWNT-AZO-NH₂, FWNT-chain-AZO with the alkyl chain between azobenzene and sidewall displayed a faster photoresponse due to weakenedÏ€-electron stacking and enough free-space for the photoisomerizion azobenzene chromophore. Polarization results preliminarily indicated the anisopic MWNT-AZO-NH₂ film due to the photo-induced alignment of nanotubes in the direction parallel to the electric field vector of polarized light by the photo-orientation of azobenzene chromphore. Results offer a great promise to fast photosensitive AZO-CNTs anisotropic film.