Semiconducting Small Molecules as Active Materials for p‐Type Accumulation Mode Organic Electrochemical Transistors

Zachary S Parr,Matteo Palma,Benjamin Poggi,Mark Freeley,Christian B Nielsen,Ellasia Tan,Isaac Abrahams,Reem B Rashid,Jonathan Rivnay,Bryan D Paulsen

doi:10.1002/aelm.202000215

Abstract

AbstractA series of semiconducting small molecules with bithiophene or bis‐3,4‐ethylenedioxythiophene cores are designed and synthesized. The molecules display stable reversible oxidation in solution and can be reversibly oxidized in the solid state with aqueous electrolyte when functionalized with polar triethylene glycol side chains. Evidence of promising ion injection properties observed with cyclic voltammetry is complemented by strong electrochromism probed by spectroelectrochemistry. Blending these molecules with high molecular weight polyethylene oxide (PEO) is found to improve both ion injection and thin film stability. The molecules and their corresponding PEO blends are investigated as active layers in organic electrochemical transistors (OECTs). For the most promising molecule:polymer blend (P4E4:PEO), p‐type accumulation mode OECTs with µA drain currents, μS peak transconductances, and a µC* figure‐of‐merit value of 0.81 F V−1 cm−1 s−1 are obtained.

Highlights

Organic electrochemical transistors (OECTs), as depicted schematically in Figure 1, have been widely explored for interfacing organic electronics with biologically and medically relevant systems.[1,2] The burgeoning field of organic bioelectronics has seen OECTs employed in a wide range of applications from neural interface devices for epileptogenic centers,[3] to biological analyte detection,[4,5,6,7] cardiac monitoring,[8] whole cell interface monitoring,[9,10] pH sensing,[11] in ion pumps,[12] and electronic plants.[13]
The relatively low currents observed for both neat P4E4 and its polyethylene oxide (PEO) blend made it difficult to extract the Organic electrochemical transistors (OECTs) charge carrier mobility with confidence and decoupling of the μC* product is the subject of further investigations. Given their often-excellent electronic charge transport properties, with mobilities exceeding those of semiconducting polymers, combined ease of synthesis and modular construction, small molecules have been widely used as active materials in organic electronics
We have shown here that mixed ionic-electronic conduction can be facilitated in small molecules through molecular design

Summary

Introduction

Organic electrochemical transistors (OECTs), as depicted schematically in Figure 1, have been widely explored for interfacing organic electronics with biologically and medically relevant systems.[1,2] The burgeoning field of organic bioelectronics has seen OECTs employed in a wide range of applications from neural interface devices for epileptogenic centers,[3] to biological analyte detection,[4,5,6,7] cardiac monitoring,[8] whole cell interface monitoring,[9,10] pH sensing,[11] in ion pumps,[12] and electronic plants.[13]. The P2E2:PEO blend (Figure 2b) exhibited an E1/2 value of 0.46 V and an onset potential of 0.34 V for the for the first oxidation event which is identical to what was observed for the neat molecule thin film.

Results

Conclusion