Yesterday I bent over in the attempt to tie the absurdly bright purple shoe laces on my almost offensively bright purple sneakers and made a startling discovery: I’m not as flexible as I used to be.  In fact, the overwhelming tightness of my hamstrings makes your standard British upper lip look positively floppy; and as I fired up my smartphone to schedule some emergency yoga I was reminded that I had yet to share an amazing new fully stretchable OLED display recently developed at the University of California, Los Angeles, a place where they know a thing or two about screens.

OLEDs or Organic Light-Emitting Diodes are great technology for screens primarily because they work without a backlight and can display deep black levels for high contrast.  OLED displays can be manufactured thinner and lighter than liquid crystal displays (LCDs) and “in low ambient light conditions such as dark rooms an OLED screen can achieve a higher contrast ratio than an LCD, whether the LCD uses either cold cathode fluorescent lamps or the more recently developed LED backlight. Due to their low thermal conductivity, they typically emit less light per area than inorganic LEDs” (Source: Wikipedia). What it all boils down to is that OLEDs are the bees knees. FACT.

Image courtesy wired.com

Once researchers saw how thin they could make OLEDs it was only a matter of time before people starting thinking about how to make them flexible. Stretchable electronics open up a world where video displays get rolled up and stuffed in your pocket, electronic sheets drape like cloth, electronics grow and shrink on command, and the mighty condor gets taken off the endangered species list.

Early attempts at stretchable electronics resulted in prototypes that connected rigid LEDs with stretchable material and others that bent but couldn’t stretch. The challenge researchers faced was how to ensure that the electrode could maintain connectivity while being deformed since many conductive materials can’t stretch nearly as far as one might like.  Enter the humble yet versatile carbon nanotube: it’s stretchable, conductive, appears transparent in thin layers, and it usually picks up the check after lunch dates.

The fly in the nanotube ointment, so to speak, is the fact that carbon nanotubes must be attached to a surface; the attachment can be tricky to pull off since when applied to a plastic backing nanotubes have a tendency to slide off or even slide past each other when the backing is stretched. To evict said proverbial fly from said proverbial ointment, the UCLA researchers created a carbon nanotube and polymer electrode layered on a stretchable, light-emitting plastic.

The researchers “coated carbon nanotubes onto a glass backing and added a liquid polymer that becomes solid yet stretchable when exposed to ultraviolet light. The polymer diffuses throughout the carbon nanotube network and dries to a flexible plastic that completely surrounds the network rather than just resting alongside it. Peeling the polymer-and-carbon-nanotube mix off of the glass yields a smooth, stretchable, transparent electrode” (Grifantini).  I imagine that the carbon nanotubes embedded in the plastic stretch at roughly the same rate, and that the plastic keeps to itself mostly and doesn’t interfere with the ability of the nanotubes to conduct electricity.

Image courtesy pcworld.com

The team sandwiched two layers of carbon nanotube electrode around another plastic that emits light when current runs through it.  Researchers obtained a laminator from a local office supply store to press the layered device together so that it could be handled safely in the presence of electric current.  As an aside, we did the same thing when we screen printed an electroluminescent lamp in Switzerland this summer and were hoping to not get electroshocked by the circuits. (More on that soon).  In contrast to our electroluminescent display, the flexible OLED created by the UCLA team can be stretched by as much as 45 percent while emitting a colored light.

Their prototype is a two-centimeter square that emits a one-centimeter square brilliant sky-blue light that stretches like silly putty until it loses conductivity due to being stretched too far or too many times (Grifantini).  The researchers also made a prototype using silver nano wires (which are more conductive than nanotubes) that exhibits similar stretching properties but is even more conductive.  Their layered approach is a great idea, not least because it’s easy to imagine how the process could be scaled up for production.  Now if only those scientists could help me with my hamstrings….

WU XING:

I have filed stretchable OLEDs under Water, Wood and Fire because they’re flexible, stretchy, and they light up.

Cited:

Grifantini, Kristina. “The First Fully Stretchable OLED.” Techreview.com 08/26/11. Accessed 10/05/11. URL.

Watch video: Stretchable OLED – Tech Review

Image courtesy physorg.com

Energy start-up NextGen thinks their solar paint has the potential to go 100,000 miles without batting an eye (so to speak).  Their “new breed of cheap solar paint is closer than ever now that the company has raised half of the $1 million it needs to move out of the lab and into the real world. The company’s solar paint is expected to provide up to 40% efficiency at a third of the cost of traditional photovoltaic panels. That’s partially because the paint captures more wavelengths of light than traditional cells. The material, which forms small connected solar cells as it dries, can be applied to nearly any surface–windows, walls, roofs, and more” (Schwartz). It would be easy to repair damaged paint too – you’d just apply another coat.

Image courtesy gliving.com

NextGen isn’t the only organization working on solar paint and spray-on solar cells; others include the National Institute of Standards and Technology, the University of Texas, and the National Renewable Energy Laboratory (Schwartz).  At UT, a research group is making nanocrystals out of copper, indium, gallium, and selenide, dispersing small particles of the inorganic material in a solvent to create an ink or paint that can be sprayed on plastic, glass, and even fabric to create a solar cell. Nanocrystals and nanotubes 10,000 times thinner than a strand of human hair absorb a larger number of light wavelengths onto the photovoltaic cell. The paint can be applied to almost any surface and once dry hooks into the light-sensitive grid to start pumping out electricity (Stefano).

Image courtesy homepage.mac.com

Solar paint technology would be a good fit for something like a government buildings where solar paint could offset energy consumption while giving taxpayers a break, but it should be noted that solar paint is still bleeding edge and “has yet to prove itself in a commercial setting. But if it is successful, NextGen’s paint could help reach the elusive goal of bringing solar power down to price parity with coal power” (Schwartz).  Another issue researchers face is finding raw materials can be used if this technology can be mass produced; copper, indium, gallium, and selenide are not particularly cheap nor are they readily available. Challenges acknowledged, I have a feeling that if this works out we’ll all be slathering our homes and businesses with solar paint and selling energy back to the grid. Then we’ll all go out and buy Lamborghinis.

WU XING:

While it seems somewhat paradoxical, I have filed solar paint under FIRE because it generates electricity, and under WATER because it is a coating.

Cited:

O’Brien, Miles and Marsha Walton. “Getting a Charge out of Solar Paint.” Physorg.com 02/14/11. Accessed 02/16/11. URL.

Stefano, Greg. “Nano Solar Paint: Liquid cells potentially reinvigorate solar power industry.” Coolhunter.com 09/30/10. Accessed 02/16/11. URL.

Schwartz, Ariel. “NextGen Announces Cheap Solar Paint on the Horizon.” Inhabitat.com 04/12/10. accessed 02/16/11. URL.