Reversible stress-induced doping and charge trap generation in IDT-BT EGOFETs

Electrolyte-gated organic field-effect transistors (EGOFETs) have great potential for highly sensitive and affordable biosensors due to their low operating voltages and adaptable device geometry, facilitated by the large double layer capacitance in the electrolyte. While high performance biosensors have been attained using a variety of materials and device structures, the operational stability of EGOFETs remains poorly understood. Polythiophenes such as P3HT and pBTTT are the most commonly used organic semiconductors in these devices owing to their high hydrophobicity and well-known film and transport properties. However, in conventional OFETs they have been surpassed both with regards to performance and stability. Poly[2,1,3-benzothiadiazole-4,7-diyl-co-4,4,9,9-tetrahexadecyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl] (IDT-BT) is a donor-acceptor copolymer and one of the best performing and most stable OFET materials. While it has been shown to work in an EGOFET setting as well, the long-term operational stability of such devices, crucial to their eventual application in clinical settings, is poorly understood. In this work, we show that IDT-BT based EGOFETs undergo reversible stress-induced doping, but that they nonetheless achieve a high degree of operational stability and a lifetime in excess of 100 hours under bias. Furthermore, we observe that long-term performance degradation is connected to semiconductor surface changes, seen as increased roughness and reduction in capacitance.