Synthesis of multifunctional carbon nanomaterials for device applications.

摘要

Owing to their excellent electrical, optical and mechanical properties, carbon nanomaterials, such as single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and graphene, are attractive for a large variety of applications, including sensors, smart nanocomposites, solar cells, organic light emitting diodes (OLEDs), and field effect transistors (FETs). For most of these, and many other applications, it is necessary to chemically or physically functionalize carbon nanomaterials with other organic/inorganic or polymeric materials. In this context, carbon nanotubes and graphene have been functionalized with TiO2 nanoparticles, poly(3-hexylthiophene) (P3HT), and/or C60 as transparent conductive electrodes or active materials in optoelectronic devices, namely organic photovoltaic cells (OPVs). Some more specific work carried out during this study is summarized below.;1) A class of new conjugated copolymers containing fluorine donor and quinoxaline acceptor was synthesized via Stille coupling polymerization. They are used to increase the open circuit voltage and short circuit current of bulk heterojunction solar cells as the increase of quinoxaline ratio in the copolymers could lead to a broadened solar absorption spectrum and decreased highest occupied molecular orbital (HOMO).;2) P3HT chains were grafted onto MWNTs via formation of ester bond linkages between P3HTs and MWNTs functionalized with hydroxyl and carboxylic groups, respectively. The resultant P3HT-grafted MWNT (P3CNT) was used as electron donor and charge transport materials in bilayer and bulk heterojunction solar cells, respectively, to improve the device performances as the large surface area and good electrical properties of MWNTs can not only increase the exciton dissociation efficiency but also improve the charge carrier mobility.;3) C60 was grafted onto graphene sheets (C60-g-Gra) via anionic reaction with n-butyllithium. It was found that addition of C60-g-Gra into P3HT:PCBM composites in bulk heterojunction solar cells could lead to improved short circuit current and open circuit voltage with no obvious change in the fill factor.;4) Bilayer- and bulk-heterojunction solar cells based on liquid crystalline porphyrins as a donor (C13Por and C13Zn) and C60 or PCBM as an acceptor were fabricated by all solution processing. Thermal annealing of these solar cells induced the homeotropic alignment of porphyrins in the photoactive layer, leading to an efficient hole conduction along the columnar axis and light absorption over the large surface area of porphyrin columns, and hence a factor of 2-3 times increase in the power conversion efficiency.;5) Transparent and conductive films supported by a polydimethylsiloxane (PDMS) substrate were fabricated by mixing SWNTs with TiO2 attached MWNTs (TiO2-MWNTs) using a spray method. Due to the photoactive nature of TiO2 to UV light, photocurrent was detected from the resultant transparent and conductive films.;6) Nanohybrids of single-walled carbon nanotubes (SWNTs) and pyrene chromophores were prepared by ruthenium (II) metal complexation. The resultant nanohybrids showed the metal-to-ligand-charge-transfer (MLCT) at 525 nm, which is 27-nm redshift compared to that of 495 nm of model compound due to the electron withdrawing properties from SWNTs. Thus, the complexation and decomplexation of ruthenium (II) in the nanohybrids could be used for sensing applications.