Abstract: Ultrathin flexible organic optoelectronics have attracted growing interest for wearable and bio-integrated applications because their reduced thickness enables superior mechanical compliance and conformal contact compared with conventional flexible devices. These advantages are particularly important for human health monitoring, where intimate and stable contact with soft, curvilinear skin is essential for accurate signal acquisition. However, traditional flexible organic optoelectronic devices, typically thicker than 100 μm, often suffer from interfacial delamination, stress concentration, and degraded electrical stability under repeated deformation. Here, we present our previous efforts on the fabrication and structural engineering of printable ultrathin organic optoelectronic devices with total thicknesses below 10 μm. By combining interfacial material design with mechanical architecture optimization, we developed ultrathin device platforms that improve energy-level alignment, enhance interlayer adhesion, and reduce strain localization in multilayer structures. Representative devices based on ~1.5 μm polymer substrates and ultrathin encapsulation layers exhibited excellent flexibility, maintaining stable operation under bending radii down to 0.5 mm and after up to 10,000 bending cycles. Compared with conventional thick flexible electronics, these ultrathin architectures show greatly improved deformability, interfacial stability, and tolerance to cyclic mechanical loading. Our studies demonstrate that interface engineering, together with rational structural design, is essential for constructing mechanically robust and electrically stable ultrathin organic optoelectronics, providing useful guidelines for future wearable health monitoring, soft bio-interfaces, and highly compliant organic electronic skins.

Keywords: Ultrathin organic optoelectronics, interface engineering, flexible electronics, printable electronics, interfacial adhesion, cyclic deformation.

Biography: Dr. Lulu Sun is a Research Scientist at RIKEN and a visiting researcher at the University of Tokyo. His research focuses on flexible organic electronics, with particular emphasis on developing ultrathin flexible organic optoelectronic devices for human health monitoring. Through interface engineering, he aims to improve device mechanical flexibility and adhesion to biological tissues. He has published over 60 papers, including first- or corresponding-author articles in Nature Energy, Nature Communications, and Science Advances. Some of his publications have been recognized as ESI Highly Cited Papers. His work has received broad media coverage, including coverage by NHK, Nikkan Kogyo Shimbun, and Bunkyo Shimbun. He has received several honours, including the RIKEN Research Incentive Award, and has presented at major international conferences such as MRS and PVSEC. He also serves as a reviewer for leading journals and as a Young Editorial Board member of FlexMat and SmartSys.