Lucas Flagg1,Jonathan Onorato2,Christine Luscombe3,2,Lee Richter1
NIST1,University of Washington2,Okinawa Institute of Science and Technology3
Lucas Flagg1,Jonathan Onorato2,Christine Luscombe3,2,Lee Richter1
NIST1,University of Washington2,Okinawa Institute of Science and Technology3
Organic Electrochemical Transistors (OECTs) are an important platform for benchmarking emerging applications in polymeric mixed ionic/electronic conductors. In such applications, the polymer semiconductor is swollen by the electrolyte, which leads to drastic changes in design rules compared to the more well understood alkyl-side chain polymers that have been studied for flexible electronic applications for the past few decades. Here we study the model mixed conductor poly(3-(methoxyethoxyethoxymethyl)thiophene) (P3MEEMT) as a function of molecular weight, thermal annealing, and regioregularity. We first show that OECT performance increases with increasing molecular weight. We next show that low molecular weights are unable to withstand even moderate thermal treatments. We hypothesize this is due to less inter-crystal connections in the lower Mn polymers and that this detrimental effect is enhanced in OECTs, compared to conventional Organic Field Effect Transistors (OTFTs), due swelling. Finally, we investigate the role of regioregularity on the OECT performance. Surprisingly, we find reduced regioregularity increases the volumetric capacitance of these films at the expense of carrier mobility. However, these competing effects tend to offset resulting in device performance that is largely independent of regioregularity. These findings will help establish design rules for novel polymeric mixed conductors going forward.