In a paper titled "Aqueous Processing for Printed Organic Electronics: Conjugated Polymers with Multistage Cleavable Side Chains" published in the ACS Science Central journal, the researchers describe a multistage cleavable side chain method whereby active semiconductor polymers are first synthesized and purified in organic solvents, before being converted to a water-soluble form for safe aqueous processing. After printing, the ink is exposed under a UV lamp to cleave off the added chemical trigger that enabled the solubility conversions. Once cured, the pure organic semiconductor can no longer dissolve in water or organic solvents.
As a proof-of-concept for their new processing method, the researchers used an organic soluble polythiophene to obtain an aqueous printed electrochromic thin-film. But in their paper, they note that adding multistage cleavable side chains to electroactive conjugated polymers could become a universal method for aqueous printing in organic electronics.
By extension, it is the whole printable electronics industry that could benefit from this new method, removing the risks and handling costs associated with aromatic or chlorinated organic solvents. The new method could lend itself to print organic field effect transistors (OFETs), OLEDs, biosensors and more.
Starting with electrochromic film inks, making them safer to use could give them a boost for many applications. According to Reynolds, those can be made in any color and could be applied to various materials beyond plastic and window panes.
"You could apply this to camouflage, for example, with the right textiles, and have a sensor connected to a battery, and have it switch the colors to match the changing lightness or darkness of a soldier's surroundings", expressed the researcher on Georgia Tech's news blog. Next, the researchers will experiment with various methods of printing or spraying.
By Julien Happich