The thermoelectric generator (TEG) developed at the Laboratory of Organic Electronics at Linköping University uses an organic composite material with unique properties. It soft and stretchable with a high electrical conductivity and good thermoelectric properties. This makes it ideal for many wearable applications such as smart clothing, wearable electronics and electronic skin.
The TEG combines the conducting polymer PEDOT:PSS for the thermoelectric properties, a water-soluble polyurethane rubber for elasticity and an ionic liquid for softness. This generates a thermelectric generator with a high conductivity of over 140 S/cm that can stretch to six times its length. A test module showed an output of 212 μV/K, and when the module was connected to varying load resistors it showed a maximum power output at a load of 430 Ω, which corresponds to the total resistance of the module. At this load the maximum power output was 25nW for a temperature difference of 30 K, which was the theoretical maximum. The advantage of the new material is that large amounts can be used to increase the total power output.
PEDOT:PSS is the most common conducting polymer and is used in many applications, not least due to its good thermoelectric properties. But thick polymer film is too hard and brittle to be successfully integrated into wearable electronics. “Our material is 100 times softer and 100 times more stretchable than PEDOT:PSS,” said Klas Tybrandt, who leads the group of Soft Electronics at the Laboratory of Organic Electronics. “The ability to control the structure of the material both at the nanoscale and the microscale allows us to combine the excellent properties of the different materials in a composite,” he said.
The new composite is also printable. “The composite was formulated by water-based solution blending and it can be printed onto various surfaces. When the surface flexes or folds, the composite follows the motion. And the process to manufacture the composite is cheap and environmentally friendly,” said researcher Nara Kim (above).
The researchers see a huge range of new possibilities using the material to create soft and elastic organic conducting materials. “There are many ionic liquids, conducting polymers and traditional elastomers that can be combined to give new nanocomposites for many applications, such as thermoelectric generators, supercapacitors, batteries, sensors, and in wearable and implantable applications that require thick, elastic and electrically conducting materials,” said fellow researcher Xavier Crispin.
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