Infinite power supply for wearables

Researchers at KAIST have increased the energy efficiency of a piezoelectric nanogenerator by almost 40%. The development takes us a step closer toward the commercialisation of flexible energy harvesters that can supply power infinitely to wearable, implantable electronic devices.

Nanogenerators are innovative self-powered energy harvesters that convert kinetic energy created from vibrational and mechanical sources into electrical power, removing the need for external circuits or batteries for electronic devices. Nanogenerators, a flexible and lightweight energy harvester on a plastic substrate, can scavenge energy from the extremely tiny movements of natural resources and the human body, such as wind, water flow, heartbeats and diaphragm and respiration activities to generate electrical signals. However, poor energy efficiency and a complex fabrication process have posed challenges to the commercialisation of nanogenerators.

KAIST researchers have recently proposed a solution by developing a robust technique to transfer a high-quality piezoelectric thin film from bulk sapphire substrates to plastic substrates using laser lift-off (LLO).Applying the inorganic-based laser lift-off (LLO) process, the research team produced large-area PZT thin film nanogenerators on flexible substrates (2 x 2 cm).

“We were able to convert a high-output performance of ~250 V from the slight mechanical deformation of a single, thin plastic substrate. Such output power is just enough to turn on 100 LED lights,” Keon Jae Lee explained.

The self-powered nanogenerators can also work with finger and foot motions. For example, under the irregular and slight bending motions of a human finger, the measured current signals had a high electric power of ~8.7 μA. In addition, the piezoelectric nanogenerator has world-record power conversion efficiency, almost 40 times higher than previously reported similar research results, solving the drawbacks related to fabrication complexity and low energy efficiency.

Lee further commented, “Building on this concept, it is highly expected that tiny mechanical motions, including human body movements of muscle contraction and relaxation, can be readily converted into electrical energy and, furthermore, acted as eternal power sources.”

The research team is currently studying a method to build three-dimensional stacking of flexible piezoelectric thin films to enhance output power, as well as conducting a clinical experiment with a flexible nanogenerator.