16:00-16:15

Toward NIMS/MANA-Flinders Univ. Research Collaboration

Speaker

Dr. Kohei Uosaki, MANA Principal Investigator, MANA, NIMS

16:15-17:00

Use of Carbon Nanotubes in Novel Solar Cells

One of the most important issues facing society is the ability to supply the world’s energy requirements via both environmentally responsible and sustainable means. Renewable energy, and in particular solar energy, has the potential to address current issues in energy production but costs, both in terms of the energy required for production and final price to the consumer, as well flexibility in terms of system deployment are problems that will need to be addressed. This talk will focus on work using carbon nanotubes to make new architectures for solar cells. Several possible structures will be explored and the disadvantages and advantages of each will be examined. Single walled carbon nanotubes are an allotrope of carbon having unique electrical and optical properties and are promising as future photovoltaic materials and it is thus important to investigate methods of exploiting their properties in photovoltaic devices.

The photovoltaic properties of a new working electrode for dye sensitised solar cells, consisting of networks of covalently bound single walled carbon nanotubes on indium tin oxide have been investigated. Following covalent sensitisation of the carbon nanotube networks with a ruthenium dye an appreciable cathodic photocurrent is measured upon illumination with simulated sunlight. By building up sequential layers of carbon nanotubes cross-linked with ethylenediamine to form a three dimensional dye sensitised single walled carbon nanotubes network significant increases in photocurrent density are observed.

Vertically aligned single walled carbon nanotube arrays were created on an optically transparent electrode (Fluorine doped tin oxide coated glass, FTO) by a self assembly process This lead to arrays of SWNT chemically attached to the substrate that when exposed to visible light exhibited a prompt current response. This photoresponse behaviour was investigated by modifying the attachment conditions and also the SWNT treatment procedures. The nanotube arrays were found to have a tunable current and voltage response and serve as a possible scaffold for further fuctionalisation. Chemical modification of these thin (<200nm) arrays with PAMAM-type dendrons has been undertaken to enhance the photoresponse of these devices. The effect of modification on the electrode was measured by differential pulse voltammetry to detect the dendrons, and the effect on the nanotubes was measured by Raman spectroscopy. Solar simulator illumination of the cells was performed to measure the effect of the nanotube modification on the cell power, and determine the optimal modification. Electrochemical impedance spectroscopy was also used to investigate the equivalent electronic circuit elements of the cells. The optimal dendron modification occurred with the second generation (G-2.0), which gave a 70% increase in power over the unmodified nanotube array.

In addition to already extensive research using carbon nanotubes in organic photovoltaics and photoelectrochemical cells, another way to exploit nanotubes in solar cells is to combine them with a relatively well understood model semiconductor such as silicon. This solid state architecture explores nanotube-silicon heterojunction solar cells that show promising results in terms of efficiencies and fill factors and can be made relatively simply. The cells exploit the photoactivity of carbon nanotubes as well as use the underlying silicon to harvest the light. Nanotube-silicon heterojunction solar cells are a recent photovoltaic architecture with demonstrated power conversion efficiencies of up to ~14 % that may in part exploit the photoactivity of carbon nanotubes. Whilst the architecture is still relatively new it shows great promise for a viable new approach to solar cells and indeed opens up new possibilities for more novel solar cell architectures.

Speaker

Prof. Joseph G. Shapter, School of Chemical and Physical Science, Flinders University, Australia

Chair

Dr. Tomonobu Nakayama, MANA Principal Investigator, MANA, NIMS

17:00-17:45

Growth of Single-layer Graphene and Hexagonal Boron Nitride on Metal Substrates

The typical sp²–bonded two dimensional materials such as graphene and hexagonal boron nitride (h-BN) layer with honeycomb crystal structure, have attracted special interests in both fundamental research and potential applications because of their remarkable properties and chemical stability. High quality graphene and h-BN layers can provide new opportunities in potential applications, however, the large scale fabrication of graphene and h-BN with large percentage of single layer is still a challenge. Therefore, synthesis of single-layer graphene and h-BN is highly desirable. Here we report the fabrication of single-layer graphene on carbon-doped single-crystal Pt(111) (0.05 %) substrate. It is found that single-layer graphene islands can form on Pt(111) surfaces, the size can be up to about 50µm. The atomic structure of graphene islands has been investigated by scanning tunneling microscopy (STM), which exhibit hexagonal atomic lattice, indicating the weak interaction between graphene and the Pt(111) substrate. Secondly, we synthesized the single-layer and few-layer h-BN on Fe-Cr-Ni alloy by surface segregation. We found that the triangular shape of h-BN flakes can be formed. The present synthesis can provides a novel technique for atomically graphene and h-BN layer fabrication.

Speaker

Prof. David Lewis, School of Chemical and Physical Science, Flinders University, Australia

Chair

Dr. Kohei Uosaki, MANA Principal Investigator, MANA, NIMS