A Solution-Based Deposition Method Enabling Pigment Blue Edible Electrochemical Transistors

Abstract

Copper(II) phthalocyanine (CuPc), also known as Pigment Blue 15, is a widely utilized pigment renowned for its exceptional semiconducting properties when refined to electronic-grade purity. Recent studies have confirmed its safety if ingested at doses required for essential active components in edible electronics for advanced gastrointestinal tract monitoring. Since in-body operations impose stringent safety constraints on operational biases, the development of transistors with high transconductance at low voltages is required to ensure adequate amplification gain. This study presents a simple and cost-effective method for producing solution-processed CuPc films characterized by a unique porous microstructure that facilitates efficient volumetric ion uptake and mixed ionic-electronic conductivity in electrolyte-gated devices. These porous films exhibit capacitance 30 times greater than compact CuPc films produced through conventional physical vapor deposition methods. The resulting edible transistors demonstrate On/Off ratios exceeding 10³ and channel width-normalized transconductance of up to 50 µS mm⁻¹ at 0.8 V, establishing their potential as critical active components in future edible devices. Moreover, the proposed method results in a limited impact of impurities on CuPc charge transport efficiency, thus affecting the purification costs and, crucially, enabling the sourcing of CuPc pigments through recycling and upcycling.