Recent advances in soft materials and mechanics activate development of many new types of electrical medical implants. Electronic implants that provide exceptional functions, however, usually require more electrical power, resulting in shorter period of usages although many approaches have been suggested to harvest electrical power in human bodies by resolving the issues related to power density, biocompatibility, tissue damage, and others. Here, we report an active photonic power transfer approach at the level of a full system to secure sustainable electrical power in human bodies. The active photonic power transfer system consists of a pair of the skin-attachable photon source patch and the photovoltaic device array integrated in a flexible medical implant. The skin-attachable patch actively emits photons that can penetrate through live tissues to be captured by the photovoltaic devices in a medical implant. The wireless power transfer system is very simple, e.g., active power transfer in direct current (DC) to DC without extra circuits, and can be used for implantable medical electronics regardless of weather, covering by clothes, in indoor or outdoor at day and night. We demonstrate feasibility of the approach by presenting thermal and mechanical compatibility with soft live tissues while generating enough electrical power in live bodies through in vivo animal experiments. We expect that the results enable long-term use of currently available implants in addition to accelerating emerging types of electrical implants that require higher power to provide diverse convenient diagnostic and therapeutic functions in human bodies.

The recent commercial success of flexible and foldable displays has resulted in growing interest in stretchable electronics which are considered to be the next generation of the optoelectronic technology. Stretchable display technologies are being intensively studied for versatile applications including wearable, attachable, and shape changeable electronics. In this paper, we present high fill factor, stretchable inorganic light-emitting diode (LED) displays fabricated by connecting mini-LEDs and stretchable interconnects in a double-layer modular design. The double-layer modular design enables an increased areal coverage of LEDs and stretchable interconnectors with both electrical and mechanical stability. The main features of the double-layer modular design, fabrication processes, and device characteristics for the high fill factor, stretchable inorganic LED display are discussed, with experimental and computational results. Demonstrations of a passive matrix LED display confirm the potential value of the multi-layer structured, stretchable electronics in a wide range of applications that need high fill factor with high stretchability.

Among these, wireless power transfer via RF inductive coupling has the advantage of providing relatively high power. [31,32] However, RF wireless power transfer may have limited efficiency when the transceiver is miniaturized [16,33,34] or misaligned. [28,31] The technology using photovoltaics can also provide adequate electrical power to implants by capturing ambient light [24,36] or capturing light from an external light source. [37,38] While these technological advancements are encouraging, the characteristics of electrical performance when using devices under deformation or misalignment caused by opaque soft skin tissues have not yet been reported. The electrical performance characteristics are essentials in integrating reliable power systems to various electronic implants Herein, we report the electrical performance characteristics of a PV implant and external light source patch depending on misalignment, implantation depth, and deformation, which may occur in practical applications. Our experimental studies included ex vivo trials with a PV implant under an animal skin whose surface was covered by an attachable light source patch. We varied the lateral misalignment distance, implantation depth, and bending radius and direction. These results should be useful in the design and application of wireless power transfer using light for implantable medical electronic devices.

Lightweight ultrathin solar cells with high efficiency and reliability serve as a convenient untethered power source for new types of electronic devices, such as attachable or implantable electronics, small‐scale robots, and many others. However, the extreme mechanical properties of high‐performance solar cells and ultrathin films present challenges when handling and processing them to realize ultrathin solar cell arrays. In this paper, a highly efficient GaAs photovoltaic array integrated on an ultrathin polymer film (1.4 µm thick) is presented. Full processes, including framing, cold‐welding, epitaxial lift‐off (ELO), and microfabrication, are used to realize ultra‐flexible and lightweight GaAs photovoltaic arrays. The mechanical characteristics are analyzed via numerical and experimental methods along with demonstrations with electrically functional devices. The power‐to‐weight ratio (specific power: 5.44 W g−1) is in the highest range, even with single‐junction solar cells.

This image demonstrates an ultrathin GaAs solar cell hanging on a thin thread. After coldwelding and epitaxial lift-off processes, the ultrathin GaAs solar cell is transferred on a 1.4 μm thick polymer film substrate. The lightweight and ultra-flexible characteristics of the polymer substrate helps the GaAs solar cell to be applied on unconventional surfaces. More information can be found in article number 2200344 by Jongho Lee and co-workers.