Could plastic lights supercede compact fluorescents?
Francis Sedgemore, Monday 3 December 2012 at 14:29 UTC
There is an interesting story on a novel lighting technology doing the rounds following the recent publication of an academic paper by a research group based at a small liberal arts college in South Carolina. I have yet to read the paper as it is published in a journal to which I do not have easy access. However, while I cannot discuss the detail of that paper, I can comment on the broader scientific and engineering principles involved, which have for some time been under investigation within the nanoscience and technology research community.
Physicist David Carroll and his colleagues at Wake Forest University have used the effect known as field-induced polymer electroluminescence (FIPEL) to produce a plastic light bulb that more closely mimics the spectrum of the Sun than do compact fluorescent bulbs with their slightly blueish tinge. Other advantages of FIPEL-based devices are that they can be made into any shape, contain no mercury, and do not shatter.
FIPEL involves running an electric current through a conductive polymer that has been deliberately contaminated with carbon nanotubes. The effect of the nanotubes is to increase the achievable luminance of the otherwise weakly fluorescent polymer by around five times. The physics and electro-chemistry of this luminance boost are the subject of the Carroll group paper, and there are other groups around the world looking at the same and similar charge injection effects. Differences between these projects include the types of nanomaterials used as doping agents.
Curly compact fluorescent bulbs have failed to attract public support, though for environmental and other reasons they are replacing incandescent lighting. Another once promising lighting technology is based on organic light-emitting diodes (OLEDs), but there are problems with the fabrication and longevity of materials that rapidly degrade on exposure to air and humidity. OLEDs have found favour with manufacturers of displays for high-end mobile phones, but the technology is not yet suitable for wider exploitation.
Non-organic LEDs are another hot topic, and they are already finding their way into new building projects as distributed light sources. One criticism of inorganic LEDs is that they have traditionally required rigid semiconductor substrates. For that reason much attention has been given to organic electronics and flexible plastic substrates, but the issues highlighted here have impacted on their development. But inorganic LEDs need not be tied to rigid substrates. Back in 2008 I had published in +Plastic Electronics a feature article about the Cambridge Cluster, aka Silicon Fen: a hub of high-tech R&D and commercial startups based around the University of Cambridge. Some of the work in Silicon Fen is concerned with the interface of inorganic nanomaterials with flexible plastic substrates, and the research is supported by some established technology firms.
All this is cutting edge applied physics and engineering research. What is attracting particular interest now in FIPEL is that patents have been awarded and capital investment sought for real-world lighting devices based on this emergent technology. But before we get too excited, we should note that there have been other promising nanotechnologies that reached the prototyping stage, but subsequently failed to translate into marketable products.
Whether Carroll, his research colleagues and as yet unnamed corporate partners succeed with their FIPEL lights will depend on a number of variables. As a journalist I have for a number of years been covering developments in nanotechnology and materials science, so I have a pretty good idea of what is involved in moving from lab to commercial nano-fab. Many much publicised ventures will go to the wall, but that is how it is with research and development.
What interests me is the success rate of projects that emerge from small laboratories such as those based in liberal arts colleges and new universities. Large-scale collaborative initiatives, often with strategic funding from state agencies, are common in nanoscience and technology, but small labs staffed by creative and enthusiastic researchers still punch above their weight.
Chen et al., “Effect of multi-walled carbon nanotubes on electron injection and charge generation in AC field-induced polymer electroluminescence”, Organic Electronics 14, 8 (2012)