– MHz-speed long-range wireless optical communication enabled by an ultra-thin, ultra-flexible near-infrared sensor

 – Published in Nature Communications, demonstrating a technological advance in ultra-thin organic photodetectors

  A research team led by Professor Hyeok Kim (School of Electrical and Computer Engineering; Department of Intelligent Semiconductor Engineering) at the University of Seoul has developed a 3μm ultra-thin, ultra-flexible near-infrared optical sensor, presenting a strategy for multi-angle, long-range wireless optical communication that overcomes the limitations of conventional organic photodetectors.

  This technology enables the uninterrupted reception of invisible light signals from distances of up to 100 m using a single thin, skin-attachable film. Even when applied to finely curved skin surfaces—such as the subtle wrinkles of a fingertip—the sensor can reliably capture optical signals without fluctuation, regardless of the angle of incidence. Consequently, it opens up new possibilities for next-generation wearable communication and healthcare technologies.

The newly developed optical sensor achieves high-speed and high-sensitivity performance, stably receiving data at speeds of up to 1 MHz across a wide range of incident angles and detecting optically modulated audio signals even at distances of 100 m. In particular, the sensor conforms closely to microscale curved surfaces comparable to fingertip wrinkles, maintaining intimate skin contact and enabling signal detection without angle-dependent performance degradation. Accordingly, it is attracting attention as a core platform for next-generation wearable healthcare and skin-conformal optical communication technologies.

▶ Research outcomes achieved in this study (left), and a schematic illustration of the device structure along with photographs of the device attached to actual skin surfaces (right)

  The research outcomes were published on December 15, 2025, in the prestigious international journal Nature Communications under the title “Skin-Conformal MHz-Speed Organic Photodetectors for Angle-Free and Long-Range Near-Infrared Communication.” This journal is a leading publication with an Impact Factor of 15.7, ranking 10th in the multidisciplinary sciences category (top 7.0% in JCR).

This study was conducted by Hyojeong Choi, a Ph.D. candidate at the University of Seoul; Jae Hyun Kim, a combined M.S.–Ph.D. student at Ajou University; and Professor Kenjiro Fukuda of the University of Osaka as co–first authors. Professor Jongin Hong of Chung-Ang University was responsible for the synthesis of the PACz interfacial material, while Professor Takao Someya of the University of Tokyo contributed to the ultra-thinning process and the design of the skin-conformal structure. Dr. Jun-gyu Choi and Researcher Jaebin Jung from Ajou University also participated as co-authors, and the research was led by Professor Sungjun Park of Ajou University and Professor Hyeok Kim of the University of Seoul, who served as co–corresponding authors.

▶ Measurement results of device durability and changes in electrical characteristics under the mechanical deformation state of the device

  Near-infrared organic photodetectors (NIR-OPDs) involve a technology that converts invisible near-infrared signals into electrical signals and are regarded as key components in a wide range of fields, including wearable healthcare, skin-conformal devices, wireless optical communication, and human–machine interfaces. Organic semiconductors are lightweight and flexible, making them highly compatible with the human body, and they offer the advantage that sensitivity, response speed, and wavelength characteristics can be freely engineered through the molecular structure design of organic devices.

  However, conventional organic photodetectors have faced inherent limitations in simultaneously achieving high-speed response, high sensitivity, and mechanical flexibility. Using highly crystalline organic films for high-speed response has resulted in reduced mechanical flexibility. Conversely, increasing flexibility has led to lower charge mobility, causing a decrease in sensitivity and speed. This has created a trade-off problem between speed, sensitivity, and flexibility. In addition, non-uniform phase separation in the photoactive layer and interfacial traps has increased charge recombination and noise, hindering the realization of high sensitivity. Furthermore, conventional OPDs fabricated on rigid substrates have struggled to maintain stable performance on finely curved surfaces at the scale of finger wrinkles (on the order of several micrometers). Angle dependence, in which sensitivity sharply decreases under oblique light incidence, has also posed a major obstacle to practical skin-conformal applications.

▶ Diagram illustrating key process parameters affecting nanoparticle productivity and the resulting changes in production efficiency

  To overcome these limitations, the research team focused on a novel interfacial engineering strategy that precisely controls charge transport pathways by forming an ultrathin layer of carbazole-based phosphonic acid (PACz) between the photoactive layer and the hole transport layer within the device. In particular, by introducing bromine (Br) into the PACz-based interfacial layer, the team further stabilized the phase distribution within the photoactive layer and enhanced charge transfer efficiency, thereby presenting a technological breakthrough that simultaneously secures high-speed response and mechanical flexibility in organic devices.

  Consequently, the researchers successfully developed an organic photodetector that, even with an ultra-thin structure of approximately 3 μm, achieves near-infrared response speeds exceeding 1 MHz, high detectivity, and stable performance across the full incident angle range of 0–90°. Furthermore, they succeeded in implementing a system capable of reliably receiving long-range wireless optical communication signals even when the device is attached directly to real human skin.

  Sungjun Park, Professor at Ajou University, stated, “This study effectively overcomes the long-standing trade-off among speed, sensitivity, and mechanical flexibility that has constrained ultra-thin organic photodetectors,” adding that “it significantly broadens the practical applicability of wearable-based optical communication and next-generation healthcare technologies.” 

  Hyeok Kim, Professor at the University of Seoul, remarked, “This work represents an important academic and technological advance in that it simultaneously achieves MHz-speed high-performance operation and angle-free characteristics even in ultra-thin, ultra-flexible structures through an interfacial engineering approach,” and noted that “it holds great potential for expansion into a wide range of wearable applications, including skin-conformal sensors and long-range wireless optical communication.”

  Meanwhile, this research was conducted with support from various government research funding programs, including the Ministry of Science and ICT, the National Research Foundation of Korea (NRF), and the Ministry of Trade, Industry and Energy, as well as support from the Semiconductor Research Center at the University of Seoul.

▶ Professor Takao Someya (corresponding author), Professor Sungjun Park (corresponding author, Ajou University), Professor Hyeok Kim (corresponding author, University of Seoul)