Navigating Bias Stress Effects for Organic Transistor Sensor Design

Electronic sensors play a key role in modern society, enabling the detection and monitoring of various physical, chemical, and biological processes. Organic field-effect transistors (OFETs) have emerged as a versatile platform for the development of this technology. However, their long-term stability and reliability are often compromised by bias stress effects, which occur upon prolonged operation. While progress has been made in the development of p-type devices, there is still a pressing need for the advancement of stable n-channel OFETs. In this work we improved the operational stability of n-type devices by utilizing the new class of donor-acceptor polymers materials based on indacenodithiazole (IDTz) and diketopyrrolopyrrole (DPP). Chemical tailoring of the electrode surface resulted in tunable charge transport and the demonstration of electron and hole injections with mobilities exceeding 1 cm²/Vs. We implemented a double layer polymer dielectric to achieve a high tolerance against bias stress and stressed the devices for 1000 min at constant DC conditions (V_GS<i></i>= V_DS<i></i>= 60V). These conditions are much more aggressive than only repeated cycling of the devices and more appropriate for applications where the transistor must provide current for long periods of time. Our OFETs exhibited negligible changes in mobility and a threshold voltage (Vth) shift = 0.5 V. Intriguingly, our findings reveal that performance and bias stress stability are not directly related when different side chain orientations are introduced on polymer backbone. Polymers with branched side chains exhibited slightly more notable degradation (average shift in mobility is 9 percent, and Vth<i> </i>= 1.2 V), although the polymer with branched side chain gave the highest mobility. In this presentation we will also describe the effect of annealing along with the structural importance of polymer and evolution of trap density of states in device stability, information of which gives clue on degradation pathways. In summary, our results provide a framework to better understanding and mitigating bias stress effects in OFETs, a crucial step for the development of stable and reliable organic electronic sensors.