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 VG ∼ −2 V while maintaining comparable current modulation (Ion/Ioff 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).