Electrochromic Displays Screen Printed on Transparent Nanocellulose‐Based Substrates

Abstract

Flexible substrates are often considered advantageous in the emerging research field of printed electronics because they add an additional feature to the resulting devices. This, in combination with transparency, is of particular interest in many electronic display applications. Traditionally, the substrates used for flexible displays are polymer-based, e.g., polyethylene terephthalate (PET), thereby preventing application areas in which sustainability is paramount. Paper-based substrates would mitigate such sustainability issues, but utilization of ordinary paperbased substrates in electronic display applications is limited due to their opaqueness. However, the opacity of traditional cellulose films has recently been overcome by the development of transparent freestanding films of nanocellulose (NC). [1,2] NC, a group of nature-derived nanomaterials, are isolated from wood and plant biomasses via various chemical, enzymatic, and/or mechanical means. Exhibiting lateral dimensions in the nanometer range and lengths reaching several micrometers, NC materials possess excellent properties, such as high aspect ratio, high specific strength, flexibility, large specific surface area, and thermal stability, combined with biodegradability and biocompatibility. [3][4][5][6][7][8][9][10] A vast variety of properties can be achieved in the production of NC-based films and fibers, for example, tensile strengths greater than cast iron, very low coefficient of thermal expansion (CTE), and transparency [1] ; the latter is of special interest in the work described herein. These properties allow for utilization in many different applications, e.g., flexible displays, [11,12] barrier films, [13][14][15][16] antimicrobial films, [17] transparent films, [1] reinforcing fillers for polymers, [18] biomedical implants, pharmaceuticals, drug delivery, fibers and textiles, [19,20] templates for electronic components, [21][22][23] separation membranes, batteries, supercapacitors, solar cells, [24] and many others. [4] A wide range of flexible electronic display technologies are already existing, or are currently being developed, but all-printed

Paper Electronics Utilizing Screen Printing and Vapor Phase Polymerization

“…[ 25,26 ] Recently, we have published a report showcasing such all‐printed electrochromic displays on transparent nanocellulose substrates. [ 20 ] While the nanocellulose substrates were almost fully transparent, they were brittle and the use of nanocellulose films as substrates is still in its infancy, which leads to slow substrate manufacturing and high costs. However, the more established transparent Cristal paper is manufactured by the roll and is more cost efficient while still maintaining good transparency.…”

“…However, a recent development in substrate formation and printing expertise has presented the conventional vertical electrochromic display structure printed on transparent nanocellulose substrates moving toward more sustainable electrochromic devices. [ 20 ] The substrates were created in a slow casting method, and the resulting substrates became brittle and therefore difficult to handle.…”

Reflective and Complementary Transmissive All‐Printed Electrochromic Displays Based on Prussian Blue

“…Conventional PEDOT:PSS‐based reflective EC displays screen printed on PET substrates typically show Δ E * values lower than 30. [ 47 ] This is to some extent contradictory because PEDOT:PSS is switched to a deeper blue color in comparison with PB. However, the high color contrast obtained in the reflective PB‐based EC devices reported here is explained by the colorless feature of PB switched to its reduced state, which visually is observed as a fully white‐colored state due to the white and opaque electrolyte in the background.…”

“…The conventional reflective PEDOT:PSS‐based EC display from RISE typically shows a maximum Δ E * value of 30, [ 47 ] depending on various process parameters. Therefore, Δ E * around 35 for the transmissive displays based on PB and PEDOT:PSS reported herein is considered very promising.…”

“…The decay from the colorless state toward the blue-colored state was approximately 24% after 10 min, while the ΔE* color contrast of the initially blue-colored state only dropped 14% during the same time. The conventional reflective PEDOT:PSS-based EC display from RISE typically shows a maximum ΔE* value of 30, [47] depending on various process parameters. Therefore, ΔE* around 35 for the transmissive displays based on PB and PEDOT:PSS reported herein is considered very promising.…”