Ultrathin and Flexible Solution-Processed Triboelectric Nanogenerators for e-Skin Applications

Triboelectric nanogenerators (TENGs) have gained significant attention due to their ability to harness low-frequency mechanical energy from environmental sources, human motion, and even human physiological activity. This enables wearable devices and sensors to self-sustain, eliminating the need for bulky and uncomfortable power sources that require regular charging or battery replacement. Here, we present an all-solution-processed polysaccharide-based TENG developed from ultra-thin and structurally robust triboelectric components. This method involves layering physically bonded graphene and nano-cellulose (NC) onto a flexible substrate, creating a durable and sustainable triboelectric component with outstanding conformability and performance suited for wearable TENG applications. The all-solution-processed devices incorporate ultra-thin active layers with an electrode thickness of ~4 μm and a tribo-layer thickness of ~6 μm, marking excellent flexibility and conformability. Mechanically refined (microfluidized) and chemically modified NCs, specifically sulfated and carboxylated forms with varying surface functionalities, were optimized to enhance TENG performance through changes in the surface potential. Notably, the sulfated, never-dried cellulose nanocrystal (NDCNC)-based TENG exhibited the highest performance when paired with polyimide (PI) as a negative triboelectric layer, achieving maximum voltage and power density values of ~1070 V and 5.76 W/m², respectively. This represents a fivefold increase in power density compared to TEMPO-oxidized cellulose nanofibril (TOCNF)-based TENG (V= 450 V, P= 1.23 W/m²). To validate the tactile capabilities of the resulting devices, peak profiling, and statistical analysis were conducted in single-electrode operation mode against various material types. Statistical methods, such as variance analysis and peak distribution studies, were employed to identify consistency and repeatability across the generated signal, allowing for precise differentiation between materials. This approach confirmed our TENG’s potential as a tactile sensor capable of accurately discerning and classifying material behaviors.