Now that personal electronics have become fashion accessories—and the fashion industry is pursuing wearable electronics—designers and manufacturers are looking to bring renewable, always available power to the human body.
So where do you mount the solar panel?
Here’s a clue: researchers in South Korea have announced a way to manufacture ultra-thin, vertical-type gallium arsenide (GaAs) photovoltaic devices that are only a quarter as thick as similar devices using a lateral design.
The approach, developed by researchers from multiple institutes in Gwangju and Gyeongsan, and funded by the National Research Foundation of Korea, uses transfer-printing to adhere ultra-thin photovoltaic devices directly onto metal electrodes on flexible receiver substrates, without needing an interlayer adhesive. At just two microns thick, this simple structure is very flexible – the solar cells in the photo are bent around a 1mm-thick edge of a glass slide. This new method can create portable solar power easily adapted for clothing and accessories.
Imagine how easily it could fit around eyeglass frames or stitched into suit jackets. Every person could fit into a personal power source that never ran out.
But how about performance? In the GaAs devices, the metal bottom layer serves as a reflector to pass sunlight that passes through back into the solar cells. As a result the researchers reported efficiency comparable to thicker photovoltaics.
While that’s not very specific, what may be more important is the power-per-weight ratio. While strapping a glass-based solar array on one’s back may be good exercise, it’s not a practical way to keep the fitness tracker juiced. Ultra-thin cells provide a better answer. For example, researchers at MIT earlier this year produced a very thin photovoltaic material using a common flexible polymer for the substrate and overcoating, and an organic material for the primary light-absorbing layer.
While the cells were not especially efficient, according to the researchers, their power-to-weight ratio was outstanding. A typical silicon-based solar module, with a glass cover, may produce about 15 watts of power per kilogram of weight. The MIT cells demonstrated an output of six watts per gram—about 400 times higher. So while the new thin cells may need more surface area for a given amount of output, they won’t weigh a garment down.
Flexibility and high power-to-weight ratios are two good reasons why ultra-thin photovoltaics may make solar energy ultra-chic.
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