Expanding the understanding of organic electrochemical transistor function

Organic electrochemical transistors (OECTs) have gained significant interest in recent years due to their ability to transduce and amplify biochemical signals into easily recorded electrical signals. The magnitude of the amplification offered by an OECT is proportional to its transconductance, g_m, making g_m an important figure of merit. Much attention has, therefore, been paid to the materials and device geometries, which can maximize an OECT's g_m. However, less attention has been paid to the role of the applied potentials and various operational regimes. In this paper, we expand on the seminal Bernards and Malliaras model of the OECT function to include negative gate potentials, allowing prediction of g_m and general biosensor performance over a broader application range. The expanded model results in five operational regimes, only two of which were covered by the original model. We find an optimal combination of drain and (negative) gate potentials yielding maximal g_m. We also find that reducing the pinch-off potential well below the water-splitting limit can yield larger operational windows at the highest g_m. Our expanded model presents a general set of guidelines for OECT operation, yielding the highest possible g_m, and, therefore, optimal amplification and associated (bio)sensor performance.