Environment

Molecular Materials

"Functional materials research is one of the top priority areas of development in science and technology in the 21st century," said Professor V.W.W. Yam of the Department of Chemistry and convenor of this theme.  The researchers brought together here will focus on developing molecular materials with functional properties, with a particular emphasis on organic optoelectronics (a theme in the previous round of this scheme). "It is highly interdisciplinary as you need chemists to create the molecular materials, physicists to understand the underlying physics, and engineers to help with the fabrication of the devices," Professor Yam said.

Molecular materials for photonic processes and electronic functions, printable electronics, and photovoltaic and other electronic applications form the three key interrelated areas of the work. Many of these materials have important implications for the environment in their applications, for example in energy efficient lighting, display technology, and electronic sensors. "Our work is strongly related to environment concerns as it is about better utilising the energy we have as well as trying to understand how we can make use of light energy to do different types of conversion," Professor Yam said.

Creating functional materials with energy efficient potential

One strand of the Molecular Materials theme is designing and synthesising new classes of metal-containing phosphorescent materials for organic light-emitting diodes (OLEDs). Such metal containing materials offer advantages in making OLEDS, such as improving their efficiencies, and HKU has a strong foundation in metal-complex chemistry.

OLED displays have low power consumption compared with say LCD because they do not use back lighting. Apart from their use in full-colour displays for a wide range of devices, OLEDs also have a tremendous potential and a number of attractive properties for solid-state lighting. Currently, incandescent lighting is still the dominant form, and most of the power used is lost as heat, with very little being used for the illumination. The solid-state lighting that could be developed using white OLEDs would have much better efficiency with very little energy lost as heat.

"A major challenge lies in the ability to produce lighting systems that can achieve high brightness at high efficiency and long device lifetime, which relies on an understanding of the role of molecular order in the charge transport and light-emitting properties of molecular thin films and the ability to design, synthesise, and characterise high purity molecular materials," Professor Yam explained.

Printing electronics for flexible devices

"Traditionally, in most optoelectronic devices, such as the colour screen of a mobile phone, the display is fabricated through vapour deposition onto a solid substrate," explained Professor C.M. Che of the Department of Chemistry. "But now there is the demand for flexible displays so you could for example roll your laptop up like paper, integrate displays into flexible fabrics such as clothing, or produce bendable solar panels." The research group is therefore developing printable electronics on flexible substrates that could be used in displays, solar cells, organic thin film transistors, sensors, and so on. To do this, they will develop novel polymer materials and also explore the implementation of the technology to fully realise the usefulness and application of the materials. The printable electronics will be cheaper to produce and the devices will use less energy than their vapour deposition counterparts.

The research group led by Professor Che has attracted substantial funding of HK$11 million from the Innovation Technology Fund through the Nano and Advanced Materials Institute and industrial sponsorship for a two-year project.  "Printable electronics will serve as one of the main propellants for the development of the next generation of display technology," Professor Che said.

Developing organic photovoltaic cells that better harvest sunlight

Another area in this theme is the development of organic photovoltaic (OPV) cells, with promising potential for substituting conventional silicon-based photovoltaic cells. "OPV cells have the advantages that they have lower production costs, high structural flexibility, and ease in molecular structural design and modification," said Professor W.K. Chan of the Department of Chemistry. "However, to date their performance is still far from that required for practical applications, and many fundamental scientific problems need to be solved and understood to design devices with improved performance."

New classes of organic and metal-organic molecular and polymeric materials for OPV cells will be designed and synthesised, the optical properties will be studied, OPV cells with different structures will be fabricated, and the device performance of the fabricated OPVs will be investigated and optimised. One application of these molecular materials for OPVs is for better harvesting solar energy and converting it to electrical power, to more fully utilise the clean, renewable source of energy provided by the sun. This work is closely related to that in the Clean Energy theme.