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Permanent, wireless self-charging system using NIR band

Professor Jung-Yong Lee

A permanent, wireless self-charging platform for low-power wearable electronics has been developed by a team at KAIST, by converting near-infrared (NIR) band irradiation to electrical energy. The researchers say this technology can be applied to flexible, wearable charging systems without needing any attachments.

Colloidal-quantum-dots (CQDs) are promising materials for manufacturing semiconductors; in particular, PbS-based CQDs have facile optical tunability from the visible to infrared wavelength region. Hence, they can be applied to various devices, such as lighting, photovoltaics (PVs), and photodetectors.

Continuous research on CQD-based optoelectronic devices has increased their power conversion efficiency (PCE) to 12%. However, applicable fields have not yet been found for them. Meanwhile, wearable electronic devices commonly face the problem of inconvenient charging systems because users have to constantly charge batteries attached to an energy source.

A joint team led by Professor Jung-Yong Lee from the Graduate School of Energy, Environment, Water and Sustainability and Jang Wok Choi from Seoul National University decided to apply CQD PVs, which have high quantum efficiency in NIR band to self-charging systems on wearable devices. They employed a stable and efficient NIR energy conversion strategy. The system was comprised of a PbS CQD-based PV module, a flexible interdigitated lithium-ion battery, and various types of NIR-transparent films.

The team removed the existing battery from the already commercialised wearable healthcare bracelet and replaced it with the proposed self-charging system. They confirmed that the system can be applied to a low power wearable device via the NIR band.

Conceptual NIR-driven self-charging system including a flexible CQD PVs module and an interdigitatedly structured LIB. b) Photographic images of a conventional wearable healthcare bracelet and a self-charging system-integrated wearable device

There have been numerous platforms using solar irradiation, but the newly developed platform has more advantages the researchers say. This is said to be because it allows conventional devices to be much more comfortable to wear and charged easily in everyday life using various irradiation sources for constant charging.

With this aspect, the proposed platform facilitates more flexible designs, which are the important component for actual commercialisation. It also secures higher photostability and efficiency than existing structures, say KAIST.

Professor Lee commented, “By using the NIR band, we proposed a new approach to solve charging system issues of wearable devices.

“I believe that this platform will be a novel platform for energy conversion and that its application can be further extended to various fields, including mobiles, IoTs, and drones.”

Illustration of the CQD PVs structure and performance of the wireless self-charging platform

Bethan Grylls

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