Self-Powered Skin-Attachable Organic Li-Fi Receiver

Light Fidelity (Li-Fi) technology, a novel communication paradigm, leverages light waves to transmit data wirelessly, offering a promising alternative to traditional radio-frequency (RF) communications. By utilizing visible light, Li-Fi enables high-speed data transfer rates that can potentially exceed those of Wi-Fi, making it a compelling solution for various applications, including smart homes, augmented reality, and high-density environments. The underlying principle involves modulating the intensity of light emitted by LED bulbs to encode information, which is then detected by photodiodes.
The need for Li-Fi technology arises from the increasing demand for faster, more reliable wireless communication. With the exponential growth of internet-connected devices, conventional RF-based systems often face challenges related to bandwidth limitations, security vulnerabilities, and interference issues. Li-Fi addresses these challenges by providing high-speed, secure, and interference-free communication, particularly in environments where RF signals may be limited or unsuitable.
However, current Li-Fi technology encounters several limitations, especially concerning the receivers. Traditional photodetectors often lack the response speed required to efficiently decode high-frequency modulated light signals. Many existing systems also rely on bulky, rigid components that restrict their deployment in versatile settings. This inflexibility can hinder the technology's integration into diverse environments, such as wearable devices or ambient lighting.
To overcome these challenges, the development of flexible, skin-attachable MHz cutoff frequency organic photodiode-based Li-Fi receivers represents a significant advancement. Such receivers can conform to various surfaces, including the human body, enabling seamless communication in close proximity while maintaining comfort and aesthetics. Additionally, organic photodiodes offer advantages such as lightweight design, low power consumption, and the potential for large-area applications. By enhancing the adaptability and performance of Li-Fi systems, these innovative receivers pave the way for broader adoption and utilization of Li-Fi technology in everyday life.
In this study, we present a self-powered, ultra-flexible organic Li-Fi receiver using a PM6:Y6 organic photodiode. We optimized the device using a carbazole-based molecule with phosphonic acid (PACz), which enhances carrier mobility and performance. Our 3-Br-4PACz sample demonstrated the highest frequency response (~1 MHz) and fastest response time compared to the other sample types. This is because it induces the vertical separation of Y6 molecules in the active layer, and thereby the charge extraction speed (which directly relates to the carrier mobility) is increased. After selecting the proper PACz type, we reduced the cell size of the 3-Br-4PACz sample to enhance response time further by reducing capacitance of the device. As a result, we doubled up the cut-off frequency up to 2MHz scale in 0.01 mm² size cell. We further optimized the cell size and validated the mechanical stability of the device, showing robust performance under repeated compression cycles (up to 1,000 times in 66% compression) and in various angular and distance settings. Not only at a 90 degree of light incidence angle but also up to 50 m distance between transmitter and receiver, the device maintained stable communication, making it ideal for wearable applications. This study represents a significant step towards flexible, high-speed, and stable wearable communication devices for future technologies.