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
