Screen-printable Electrochromic Polymer Inks and Ion Gel Electrolytes for the Design of Low-Power, Flexible Electrochromic Devices

Significance 

Electrochromic devices generally require low voltages to reach full contrast since the use of high voltage results in degradation. Therefore, designing low-power devices that can be switched over with relatively low voltages, probably less than 1V, is highly desirable. Among the available electrochromic materials, conjugated polymers have been intensively investigated for use in electrochromic applications owing to the ease in customizing their physical properties such as color control. A good example is the ECP-Magenta which exhibits high color contrast. Unfortunately, great challenges have been experienced in the attempts to construct solid and flexible systems based on conjugated polymers to facilitate the development of electrochromic applications. This requires enhancement of their rheologic properties suitable for different coating techniques such as screen-printing.

In a recent paper published in the journal, Electroanalysis, Sara Santiago, Miguel Aller, Professor Javier del Campo and Professor Gonzalo Guirado from the Universitat Autonoma de Barcelona (Autonomous University of Barcelona) and the Microelectronics Institute of Barcelona (IMB-CNM-CSIC), developed a new strategy for formulating screen-printable electrochromic inks. This approach incorporated electrochromic polymer the poly(3,4-propylenedioxythiophene) (ECP-Magenta), antimony-doped tin oxide for facilitating the electron transport, a P(VDF-co-HFP) binder, and an electrolyte. Specifically, polymeric gel electrolytes preferably ion gels were utilized to provide ions for charge-balancing and current transportation. These ion gels synthesized based on P(VDF-co-HFP) are advantages in terms of low-cost, non-volatility and high chemical stability.

As a concept of proof, the feasibility of this approach was demonstrated by constructing a fully screen-printed and flexible electrochromic device. The new ECP-Magenta ink films exhibited significant color change at low potentials up to 0.3V, higher optical values and higher coloration efficiency in comparison with other ink formulations. Consequently, the authors noted that the response time for bleaching and coloring could be improved by optimizing the film thickness. Furthermore, the formulation of electrochemical ink was observed to be compatible with the use of flexible electrolytes with minimal impact on the environment.

Ion gels comprising of the P(VDF-co-HFP) and room temperature ionic liquids showed good ionic conductivity, elasticity, flexibility, and environmental friendliness thus a promising gel electrolyte for similar applications. By analyzing the electrochemical features of different ion gels as a function of ionic liquids, new ion gels formulations were developed and incorporated in the electrochromic device. Screen-printing can be used to design and integrate the components of the electrochromic device at relatively low-cost and thus can be adapted for a wide variety of substrates for various other electrochemical devices.

This approach is scalable and can be applied to different fields. As such, this inexpensive and rapid fabrication route will open numerous doors for the preparation of similar electrochromic inks based on other polymeric compounds. In a statement to Advances in Engineering community, Professor Gonzalo Guirado, the corresponding author observed that the developed electrochromic inks and electrolyte materials will particularly facilitate the mass production of flexible electrochromic displays as well as other optoelectronic devices through screen printing.

Screen-printable Electrochromic Polymer Inks and Ion Gel Electrolytes for the Design of Low-Power, Flexible Electrochromic Devices - Advances in Engineering

About the author

Gonzalo Guirado obtained his PhD in Chemistry in 2002 from the Universitat Autònoma de Barcelona (UAB) working on molecular electrochemistry. After one-year post-doctoral training at the University of Rochester Group working on Molecular Photochemistry; he joined in 2004 the NanoSciences Group (CEMES-CNRS) in Toulouse (France) working on electrochromic and photochromic molecular switches. In 2005, he returned to the UAB where he was promoted to Associate Professor in 2010. In 2017, professor Guirado launched the “Electrochemistry and Green Chemistry Group” (Chem-Electro-Chem) at the UAB.

His recent research activities are devoted to the use of electrochemistry, Ionic Liquids and the development of electrochemically promoted “green” carboxylation processes using CO2 as a building- block for synthesizing molecular organic compounds, as well as the design of new smart switchable eco-friendly systems, paying special attention to electrochromic materials for making green devices including reusable (bio)sensos and self-powered electrochromic wearables. Up to now, he has advised 11 Ph.D. Theses, 28 Master Theses, 11 BSc Theses, published over 70 scientific articles in international journals, 3 patents and 3 book chapters.

About the author

F. Javier del Campo is Ikerbasque research professor at BCMaterials, where he leads the line on Micro- and Nanodevices. Prof. del Campo is specialized in the miniaturization of electrochemical devices, and more recently he is pioneering a research line on the electroanalytical applications of electrochromic materials. Between 2004 and 2019 he was a tenured scientist at the Microelectronics Institute of Barcelona (IMB-CNM-CSIC). His most recent activities have focused on the development of self-powered sensors based on electrochromic materials, as a means to avoid the need for silicon-based components, which earned him a Leonardo grant from the BBVA Foundation in 2016. To date, he has co-authored over 100 scientific publications (h=30), is co-inventor in 8 patents and has supervised 7 PhD theses.

His current research interests include: Electrochemistry, microfluidics, sensors and biosensors, miniaturization techniques, and systems integration.

About the author

Sara Santiago graduated from Universitat Autònoma de Barcelona (UAB) in 2016. One year later, she completed her master studies under the supervision of Dr. F.J. del Campo and G. Guirado on the design, fabrication and development of electrochromic organic devices using green electrolytes. Sara is currently joined the Electrochemistry and Green Chemistry Group and doing her PhD Thesis at the UAB.

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About the author

Miguel Aller Pellitero received his B.Sc. in Chemistry and M.Sc. in Analytical Chemistry from the University of Oviedo. In 2019, he obtained his Ph.D. in Electrochemistry from the Autonomous University of Barcelona, carrying out his research at the Institute of Microelectronics of Barcelona (CSIC).

He is currently a postdoctoral research fellow at the Johns Hopkins University School of Medicine working on the development of aptamer-based electrochemical sensing platforms for the in vivo monitoring of drugs.

Reference

Santiago, S., Aller, M., Campo, F., & Guirado, G. (2019). Screen-printable Electrochromic Polymer Inks and Ion Gel Electrolytes for the Design of Low-power, Flexible Electrochromic Devices. Electroanalysis, 31(9), 1664-1671.

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