Viney Saini

Light-harvesting using high density p-type single wall carbon nanotube/n-type silicon heterojunctions.

Photovoltaic conversion was achieved from high-density p-n heterojunctions between single-wall carbon nanotubes (SWNTs) and n-type crystalline silicon produced with a simple airbrushing technique. The semitransparent SWNT network coating on n-type silicon substrate forms p-n heterojunctions and exhibits rectifying behavior. Under illumination the numerous heterojunctions formed between substrate generate electron-hole pairs, which are then split and transported through SWNTs (holes) and n-Si (electrons), respectively. The nanotubes serve as both photogeneration sites and a charge carriers collecting and transport layer. Chemical modification by thionyl chloride of the SWNT coating films was found to significantly increase the conversion efficiency by more than 50% through adjusting the Fermi level and increasing the carrier concentration and mobility. Initial tests have shown a power conversion efficiency of above 4%, proving that SOCl(2) treated-SWNT/n-Si configuration is suitable for light-harvesting at relatively low cost.

Comparative study on different carbon nanotube materials in terms of transparent conductive coatings

We compared conductive transparent carbon nanotube coatings on glass substrates made of differently produced single-wall (SWNT), double-wall, and multiwall carbon nanotubes. The airbrushing approach and the vacuum filtration method were utilized for the fabrication of carbon nanotube films. The optoelectronic performance of the carbon nanotube film was found to strongly depend on many effects including the ratio of metallic-to-semiconducting tubes, dispersion, length, diameter, chirality, wall number, structural defects, and the properties of substrates. The electronic transportability and optical properties of the SWNT network can be significantly altered by chemical doping with thionyl chloride. Hall effect measurements revealed that all of these thin carbon nanotube films are of p-type probably due to the acid reflux-based purification and atmospheric impurities. The competition between variable-range hoping and fluctuation-assisted tunneling in the functionized carbon nanotube system could lead to a crossover behavior in the temperature dependence of the network resistance.

Carbon Nanotubes: Synthesis, Properties, and Applications

This brief review presents a comprehensive outline of the present research status on the fast moving carbon nanotube (CNT) field. It covers a short introduction to the relation between carbon nanotubes, graphite, and other forms of carbon and explains in detail the structure of CNTs. The electronic, electrical, and mechanical properties of CNTs, as well as the most widely used methods for CNT production such as electric arc discharge, laser ablation, and chemical vapor deposition (CVD), are discussed. Some of the CNT applications covered in this review article are: field emission, hydrogen storage, carbon nanotube-based solar cells, and CNT composite materials.

Large-scale graphene production by RF-cCVD method

In this work, we report a low-cost facile method for the production of few-layer graphene sheets in large quantities through radio-frequency chemical vapor deposition.

Does the wall number of carbon nanotubes matter as conductive transparent material

As electrically conductive and optically transparent thin coating material, double-wall carbon nanotube network was found to have better transparency-conductance performance as compared with single-wall carbon nanotube (SWNT) and multiwall carbon nanotube (MWNT). The electronic transportability and optical properties of the SWNT films can be altered by chemical modification of thionyl chloride. Additionally, the conductance-temperature dependence analysis revealed that variable-range hopping mechanism dominates the conductance of few wall nanotube mats while fluctuation-assisted tunneling plays a more important role in that of MWNT films.

SOCl2 enhanced photovoltaic conversion of single wall carbon nanotube/n-silicon heterojunctions

We report solar cells based on high-density p-n heterojunctions between single wall carbon nanotubes (SWCNTs) and a n-type silicon wafer. Chemical modification by thionyl chloride of the SWCNT coating films was found to significantly increase the conversion efficiency by more than 45% through adjusting the Fermi level and increasing the carrier concentration and mobility. Electron-hole pairs are optically excited in the numerous heterojunctions formed between SOCl2-treated SWCNTs thin coating and n-type silicon substrate, and then split and transported through SWCNTs (holes) and n-Si (electrons), respectively.

Organic Solar Cells: A Review of Materials, Limitations, and Possibilities for Improvement

Significant attention has been given during the last few years to overcome technological and material barriers in order to develop organic photovoltaic devices (OPVs) with comparable cost efficiency similar to the inorganic photovoltaics (PVs) and to make them commercially viable. To take advantage of the low cost for such devices, major improvements are necessary which include: an efficiency of around 10%, high stability from degradation under real-world conditions, novel optically active materials, and development of novel fabrication approaches. In order to meet such stringent requirements, the research and development in OPVs need to improve upon the short diffusion length of excitons, which is one of the factors that are responsible for their low power conversion efficiency. This review discusses some of the most significant technological developments that were presented in the literature and helped improve photovoltaic performance, such as tandem architectures, plasmonics, and use of graphitic nanostructural materials, among others. Tandem organic solar cells with embedded plasmonics are a promising approach to further increase the power conversion efficiency of organic solar cells, by harvesting complementary spectral regions with high quantum efficiencies. Polymeric nanocomposites incorporating graphitic nanostructures were extensively investigated for the next generation of efficient and low-cost solar cells, since such nanomaterials show excellent electrical and mechanical properties, excellent carrier transport capabilities, and provide an efficient pathway to the dissociated charge carriers.

Structural and optoelectronic properties of P3HT-graphene composites prepared by in situ oxidative polymerization

Poly(3-hexylthiophene) (P3HT)-graphene nanocomposites were synthesized via in situ oxidative polymerization of 3-hexylthiophene monomer in the presence of graphene. The main thrust was to investigate the structural and optoelectronic properties of P3HT-graphene nanocomposites with various graphene concentrations. NMR spectroscopy was used to determine the regioregularity of the polymer composites, whereas Fourier transform infrared spectroscopy and differential scanning calorimetry were used to study their structural and thermal properties. Moreover, cyclic voltammetry was employed to evaluate the HOMO levels of the nanocomposites, while optical spectrophotometry (UV-Vis-NIR) was utilized to determine the optical bandgap of the composites. The information from the aforementioned techniques was used to estimate the HOMO-LUMO energy levels. The results revealed changes in the optical bandgap of P3HT with increasing graphene content. Furthermore, an extensive study aiming at the effect of graphene content on...

Polymer functionalized n-type single wall carbon nanotube photovoltaic devices

Photovoltaic conversion was achieved from high-density p-n heterojunctions formed between polymer functionalized n-type single wall carbon nanotubes (SWNTs) and underlying p-type Si substrate. Functionalization of SWNTs by amine-rich polymers results in the evolution of tubes from p-type to n-type, and the polyethylene imine (PEI) functionalized SWNT film can serve as both photogeneration sites and a charge carrier collecting/transport layer. Photoremoval of oxygen adsorbed on the nanotubes prior to PEI functionalization can increase the conversion efficiency of the polymer functionalized n-type SWNT photovoltaic devices.

Catalytic Conversion of Graphene into Carbon Nanotubes via Gold Nanoclusters at Low Temperatures

Here, we present the catalytic conversion of graphene layers into carbon nanotubes (CNTs), in the presence of Au nanoparticles (AuNPs) without the need for an additional carbon source. We have demonstrated that this catalytic process takes place at temperatures as low as 500 °C. No other oxide supports decorated with AuNPs were found to grow CNTs at this temperature. These findings highlight the high activity of graphene when used as a support for catalytic reactions.