Fully Additive Vertical Organic Electrochemical Transistors on Renewable and Compostable Substrates Enable Ultrasensitive Bioelectronics

Vertical organic electrochemical transistors (vOECTs) are emerging as key building blocks for electronics and bioelectronics, offering higher drain current, transconductance, and sensitivity than planar architectures. However, current vOECT fabrication relies on photolithography, thermal evaporation, and complex microfabrication processes, which are solvent‐ and energy‐intensive, restrict substrate choice, and pose challenges for sustainable fabrication. Here, we demonstrate fully additive vOECTs fabricated via dispensing on renewable and compostable substrates. The vertically stacked architecture enables a channel length of 226 nm, resulting in high performance, with transconductance up to 36 mS, ON currents exceeding 15 mA, and drain current modulation exceeding 10 6 . By engineering source and drain electrodes through additive deposition, we minimize contact and series resistance, enabling near‐ideal charge transport and demonstrating that electrode architecture can be rationally controlled. As a demonstration of ultrasensitive bioelectronic functionality, the integration of ion‐selective membranes enables highly selective and ultrasensitive ion detection with a limit of detection (LoD) of 36 µ m and sensitivity of 1.1 mA dec − 1 . These results highlight that sustainable fabrication strategies can deliver high performance in vertical mixed ionic–electronic devices. Fully additive vOECTs on renewable and compostable substrates thus represent a promising platform for sustainable high‐performance bioelectronics.