Organic Salts—A Route to Improve Performance and Stability of N-Type Conjugated Polymers at the Electrolyte Interface

Conjugated polymers are becoming increasingly ubiquitous in bioelectronic devices operating in aqueous electrolytes, such as the organic electrochemical transistor (OECT), thanks to their mixed ionic-electronic conductivity and processability via various means.¹ However, electron-conducting (n-type) polymers are scarce and the performance and stability of the existing n-type OECTs are poor. Here, we introduce a solution-processable doping method to improve n-type OECT performance. Using organic salt blends in the polymer solution, we improve the transconductance of the n-type OECTs, stemming from an increase in electronic charge mobility. We show that although the salt cation induces a marginal doping effect, it improves the planarity of the polymer backbone and enhances the charge delocalization. Raman and electrochemical quartz crystal micro-balance studies show that the interactions of the salt with the polymer moieties (NDI or bi-thiophene) are governed by the cation type. Finally, we demonstrate that the salt-doped devices have at least one year-long lifetime while the pristine devices have limited stability. Our work provides a new and easy route to improve n-type device performance and stability in ambient conditions, which are the main bottlenecks preventing the realization of n-type organic electronic devices.<br/>1. Ohayon, D.; Inal, S. Organic Bioelectronics: From Functional Materials to Next-Generation Devices and Power Sources. Adv. Mater. 2020, 32, 2001439.