Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors.

Christian B Nielsen,Alexander Giovannitti,Muhammad R Niazi,Aram Amassian,George G Malliaras,Jonathan Rivnay,David A Hanifi,Iain Mcculloch,Dan-Tiberiu Sbircea,Michele Sessolo,Enrico Bandiello

doi:10.1021/jacs.6b05280

Abstract

The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commercially available conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, we present a series of semiconducting polymers designed to elucidate important structure–property guidelines required for accumulation mode OECT operation. We discuss key aspects relating to OECT performance such as ion and hole transport, electrochromic properties, operational voltage, and stability. The demonstration of our molecular design strategy is the fabrication of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT-based devices, and show stability under aqueous operation without the need for formulation additives and cross-linkers.

Highlights

Semiconducting materials have long played a pivotal role in the development and advancement of organic electronic applications such as organic light-emitting diodes, organic field-effect transistors, and organic solar cells.[1−4] More recently, semiconducting polymers have made their entry into the new field of organic bioelectronics, which broadly encompasses any application that couples a relevant function of organic electronic materials with a targeted biological event.[5,6]
In contrast to inorganic materials, organics can be modified for biocompatibility, while there is already a comprehensive understanding of structure−property relations from the well-established organic field-effect transistor (OFET) community.[13−15] Despite this large body of work relating to the transduction of electronic signals in organic semiconductors, high-performing bioelectronic devices such as organic electrochemical transistors (OECTs) are predominantly fabricated with the commercially available blend of poly(3,4-ethylenedioxythiophene) and polystyrenesulfonate (PEDOT:PSS).[16,17]
The intrinsically conducting nature of the PEDOT:PSS blend means that the OECT must be operated in depletion mode rather than accumulation mode, giving rise to a device that is on at no external bias and shows inferior on/off ratios at low bias, which is often desired in biological applications

Summary

■ INTRODUCTION

Semiconducting materials have long played a pivotal role in the development and advancement of organic electronic applications such as organic light-emitting diodes, organic field-effect transistors, and organic solar cells.[1−4] More recently, semiconducting polymers have made their entry into the new field of organic bioelectronics, which broadly encompasses any application that couples a relevant function of organic electronic materials with a targeted biological event.[5,6] In this context, recent endeavors have seen organic electronic materials utilized for example in biologically relevant ion sensing[7,8] and ion pumps,[9,10] and as transducers of neural activity.[11,12]. Whereas one can simplistically associate the polythiophene backbone with the charge transport and the ethylene glycol side chains with the ion transport, there is ample literature evidencing that the nature, positioning, and density of the solubilizing side chains play a huge role in the charge transport properties of the semiconducting material With this caveat in mind, we have aimed to explore synthetic design criteria in a systematic fashion in order to optimize both the charge transport and the ion transport and more importantly the product of the two (μC*). (2) TEG chain density is modulated along the polymer backbone as illustrated for example by the polymer series discussed above or by gBDT2T versus gBDT-g2T This will again have an effect on polymer solubility and packing, and importantly on the polymers’ ionization potentials (because the oxygen is directly grafted onto the thiophene ring) and their abilities to promote ion penetration/transport in the solid state. Journal of the American Chemical Society and g2T-T to investigate the role of the π-conjugated backbone and its charge transport properties without making significant changes to the backbone conformation or the side chain density

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES