The field of energy harvesting has been advancing rapidly with a considerable amount of research and development currently underway at several research laboratories across the globe.
The technology allows energy from external sources to be utilised to power a device. The efficiency is mainly dependent on the nature of the material that is used to design the energy harvesting device. Materials that have been used for energy harvesting applications include piezoelectric, thermoelectric, electrostatic and electroactive polymers.
Piezoelectric materials have a tendency to undergo mechanical deformation under the application of an external electric field and can also produce an electric field on the application of mechanical stress on the material itself. Energy harvesting solutions constitute one of the main applications of piezoelectrics. Scientists across the world are working toward developing devices that incorporate nanoscale piezoelectronics to harvest mechanical energy from ambient energy sources such as vibrations caused by footsteps. However, there are a number of challenges yet to be overcome before such devices become commercially available. The power output derived from a single piezoelectric nanowire is very small, thus requiring the integration of several wires into a larger array.
Touch screen technology is being deployed rapidly in a wide range of applications such as mobile phones, laptops, personal computers, tablet computers, e-book readers and so on. Researchers at Sungkunkwan University in Korea, together with researchers at Samsung, have devised an innovative technique of capturing power from a touch screen when it flexes under a user’s touch. On pressing a touch screen, a change is induced in the electrical potential across the nanowires that are originally used to detect the location of the touch.
Flexible and transparent electrodes have been integrated with energy scavenging materials so as to create a film capable of providing supplementary power for electronic devices. Roll-to-roll manufacturing processes can be used to print this film over large areas and can be expected to enter the market in about five years.
The device developed by the team of researchers comprises a sandwich of piezoelectric nanorods between conductive graphene electrodes on top of flexible plastic sheets. The aim of this research is to develop the flexible touch sensor system as a replacement for the power hungry electrodes and sensors that are employed on the front of touch screens. The method used to construct the nanogenerators involves growing graphene on top of a silicon substrate using the chemical vapour deposition process. In order to address the power output issue, the researchers are experimenting with doping to improve conductivity.
The researchers hope that in the future such a system could be capable of generating enough energy to even power the display of the portable electronic device and other functions as well. For example, the process of rolling up a screen could also aid in recharging the batteries. The applications that could be served by such a solution include wireless power sources for foldable, stretchable and wearable electronics.
The material developed by the researchers can generate up to 20 nanowatts per square centimetre, with further developments resulting in approximately one microwatt per square centimetre. This would be enough to power a touch sensor, thereby opening up new applications that could help realise flexible and self-powered electronic devices without the need for batteries.