Imagine a world where your smartwatch, fitness tracker, or even your shirt can power itself with your body’s movements. No more scrambling for chargers or worrying about dead batteries during an important run or a critical health check. Sounds like science fiction? Thanks to recent advancements in wearable energy harvesters, this futuristic vision is quickly becoming a reality.
A team led by Prof. Jang Kyung-In from the Department of Robotics and Mechatronics Engineering at DGIST has made a major breakthrough in this field. Their innovative 3-dimensional stretchable piezoelectric nanogenerator (S-PENG) can efficiently convert body movements into electrical energy. This technology, paired with flexible electronics, promises to revolutionize wearable tech, enabling devices that are not only smarter but also self-sustaining.
Let’s dive into the mechanics behind this exciting development and explore how flexible energy solutions are set to transform our daily lives.
Piezoelectric Energy Harvesters: A New Wave of Power
Energy harvesters typically fall into two categories: those based on the triboelectric effect and those based on the piezoelectric effect. The device created by Prof. Jang’s team uses the piezoelectric effect, which generates electricity when materials are deformed through activities like joint movements or skin stretching.
While there have been previous attempts at piezoelectric nanogenerators, most used organic or composite-based materials, which offered low energy efficiency, this limitation meant they couldn’t harvest enough power to be practical for wearable devices.
Enter lead zirconate titanate (PZT). Known for its excellent piezoelectric performance, PZT has remained underutilized in wearables because of its hardness and brittleness. But Prof. Jang’s team has ingeniously designed PZT into a three-dimensional structure that maintains its efficiency and stretchability even under deformation.
Breaking Boundaries: 280 Times Higher Efficiency
One of the most remarkable achievements of Prof. Jang’s team is their innovative S-PENG, curvature-specific coupling electrode design. By dividing the electrodes into different sections, they ensured that the device’s electrical output wasn’t canceled out by opposing charges. This S-PENG design led to an energy efficiency 280 times higher than conventional stretchable piezoelectric harvesters.
In the words of Prof. Jang: “Developing this highly efficient stretchable piezoelectric energy harvester (S-PENG) technology is a major achievement. We expect this technology to become useful after commercialization and lead to the practical use of wearable energy harvesters.”
The Rise of Flexible Electronics: A Perfect Match
The development of flexible electronics has gone hand-in-hand with these energy-harvesting breakthroughs. Originally characterized by bendable circuits and connections, flexible electronics have become smarter and more versatile thanks to nanotechnology.
Modern flexible electronics now integrate ultra-thin sensors, microprocessors, and even systems-on-chips (SoCs). These advancements are paving the way for sophisticated devices that can be worn comfortably while offering high functionality. Applications range from biomedical devices and wearable tech to smart textiles.
But for these technologies to be truly useful, we need a reliable, lightweight, and flexible power source. That’s where flexible energy harvesting-storage systems (FEHSS) come in.
Challenges of Powering Wearables: The Battery Conundrum
Traditional power sources like coin cells and rigid rechargeable batteries don’t cut it for wearables. They are bulky, and inflexible, and can compromise the device’s comfort and utility. As wearable tech evolves, we need power solutions that are:
- Flexible and Lightweight
- Efficient and Robust
- Self-Sustainable
One way to meet these needs is by improving the volumetric capacity of flexible energy storage systems. This means enhancing their energy density while maintaining safety and durability under repeated mechanical stress.
Enter Flexible Organic Photovoltaics (OPVs)
Another exciting solution for powering wearables comes in the form of Flexible Organic Photovoltaics (OPVs). These energy harvesters are lightweight, mechanically flexible, and can be produced using cost-effective techniques like roll-to-roll (R2R) manufacturing.
Recent advancements have pushed OPVs’ power conversion efficiency (PCE) to over 17% for cells and 14% for modules. This progress, driven by innovations in non-fullerene acceptor (NFA) materials and interfacial engineering, makes OPVs ideal for use in Internet of Things (IoT) devices and wearable tech.
Flexible OPVs in Action: Real-World Potential
Imagine wearing a device with an integrated flexible OPV module that harvests energy from indoor or outdoor light. Under standard 1 Sun conditions (typical sunlight), these modules can recharge batteries within hours. In low-light environments, charging might take longer, but careful power management ensures that your device remains operational.
For example, a recent breakthrough by Saifi et al. introduced an integrated 90 µm ultrathin flexible energy harvesting-storage system. This system combines:
- 4 µm ultrathin OPV modules with a power density above 10 mW/cm²
- Zinc-ion batteries with a hydrogel electrolyte thickness reduced to just 10 µm
This ultra-thin design ensures comfort and durability, making it perfect for applications in wearable textiles and health monitoring devices. The system maintains 80% efficiency after rigorous testing, including bending to a radius of less than 1 mm for 500 cycles and compression to a 10% strain for 100 cycles.
Future Outlook: A Self-Sustainable Wearable Revolution
The integration of flexible OPVs, piezoelectric harvesters, and energy storage systems is set to transform the world of wearables. Advances in material science, manufacturing, and system integration are making self-sustainable, efficient, and user-friendly wearable devices a reality.
To fully realize this potential, ongoing research must focus on:
- Enhancing Power Conversion Efficiency (PCE) for dynamic lighting conditions
- Improving Geometric Fill Factors to minimize device footprint
- Innovative Material Solutions to reduce power losses
- Ultra-Low Power Circuits to optimize energy usage
Embrace the Future of Wearable Tech
The future of wearable technology is self-sustaining and energy-efficient. Breakthroughs like the three-dimensional stretchable piezoelectric energy harvester by Prof. Jang’s team and the development of flexible OPVs are bringing us closer to a world where the devices power themselves effortlessly.
