Microfibrillated Cellulose Embedded with KCl as a Solid-Dopant Matrix into an Electrolyte-Gated Transistor

Electrolyte retention in electrolyte-gated transistors (EGTs) is typically achieved through viscous electrolytes or extra manufacturing steps for the reservoir design. In this work, we present a multifunctional solid-dopant matrix (SDM) composed of microfibrillated cellulose embedded with potassium chloride (MFC:KCl), which simultaneously acts as an electrolyte reservoir and provides ion anchoring that simplifies the device architecture and processing. For comparison, four electrolyte configurations were systematically investigated: (i) H₂O (as a nonionic reference), (ii) MFC:H₂O, (iii) KCl:H₂O (as an ionic reference), and (iv) MFC:KCl:H₂O. In water-based transistors, the MFC matrix serves as a pure electrolyte reservoir, showing water retention capability equivalent to the reference device, characterized by an on/off current ratio of ∼10², a threshold voltage of -0.13 V, a maximum drain current of ∼10^-4 A, and a maximum transconductance of ∼0.5 mS, operating within a stable electrochemical window. In KCl-H₂O-based transistors, the MFC:KCl material demonstrates dual functionality: simultaneously (i) retaining the electrolyte and (ii) compressing the operational electrochemical window (-0.2 to +0.8 V in MFC:KCl:H₂O vs -0.9 to +1.0 V in KCl:H₂O controls). This enables stable transistor operation up to V _G ∼ -2 V while maintaining comparable current modulation (I _on/I _off ratios ∼ 10³), against unstable operation of KCl:H₂O electrolyte-based devices. In addition, it presents a threshold voltage of -0.7 V, a maximum drain current of ∼10^-3 A, and a maximum transconductance of ∼ 3 × 10² mS. This study reveals that MFC offers a versatile platform for both field-effect and electrochemical transistors, aligning with green electronics initiatives by avoiding synthetic polymers like polydimethylsiloxane (PDMS).