Aqueous Processing for Printed Organic Electronics: Conjugated Polymers with Multistage Cleavable Side Chains

Abstract

The ability to process conjugated polymers via aqueous solution is highly advantageous for reducing the costs and environmental hazards of large scale roll-to-roll processing of organic electronics. However, maintaining competitive electronic properties while achieving aqueous solubility is difficult for several reasons: (1) Materials with polar functional groups that provide aqueous solubility can be difficult to purify and characterize, (2) many traditional coupling and polymerization reactions cannot be performed in aqueous solution, and (3) ionic groups, though useful for obtaining aqueous solubility, can lead to a loss of solid-state order, as well as a screening of any applied bias. As an alternative, we report a multistage cleavable side chain method that combines desirable aqueous processing attributes without sacrificing semiconducting capabilities. Through the attachment of cleavable side chains, conjugated polymers have for the first time been synthesized, characterized, and purified in organic solvents, converted to a water-soluble form for aqueous processing, and brought through a final treatment to cleave the polymer side chains and leave behind the desired electronic material as a solvent-resistant film. Specifically, we demonstrate an organic soluble polythiophene that is converted to an aqueous soluble polyelectrolyte via hydrolysis. After blade coating from an aqueous solution, UV irradiation is used to cleave the polymer’s side chains, resulting in a solvent-resistant, electroactive polymer thin film. In application, this process results in aqueous printed materials with utility for solid-state charge transport in organic field effect transistors (OFETs), along with red to colorless electrochromism in ionic media for color changing displays, demonstrating its potential as a universal method for aqueous printing in organic electronics.

The Effects of Side Chains on the Charge Mobilities and Functionalities of Semiconducting Conjugated Polymers beyond Solubilities

“…In particular, the light‐emitting CPEs have been widely explored for biosensing and imaging . In recent years, new CPEs have been designed and investigated to improve charge injection in OLEDs, charge extraction in OPVs, and OFETs . CPEs were also used as sensitizers in dye‐sensitized solar cells .…”

Organic light emitting diodes (OLEDs) with slot-die coated functional layers

“…While necessary for high performance, the multi-layer OLED configuration presents significant challenges for printing/coating where each layer must be immiscible with the solvent being processed on top. Thus, for the socalled orthogonal solvent processing, developing solvent resistant films via chemistry 65,66 and careful solvent selection [67][68][69] , are both crucial research areas.…”

Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V

“…These polyelectrolytes have received considerable attention as interlayer materials to tune the work function of OSC electrodes but have rarely been investigated as water/alcohol-processable active materials [20]. This is mainly due to the fact that the ions in the pendant chains will strongly respond to the applied bias [21]. Owing to their peculiar optoelectronic properties, polythiophenes and their derivatives have been extensively studied and are often considered state-of-the-art electron donors for OSC active layers [22,23].…”