Self-aligned patterning of conductive films on plastic substrates for electrodes of flexible electronics

Abstract

We report a reliable and low-cost self-aligned patterning process for the formation of conducting polymer electrodes with a high resolution on flexible plastic substrates. To realize high resolution and self-aligned patterning on the poly(ethylene 2,6-naphthalate) substrate, hydrophilic hydroxyl anchoring groups are formed by the photochemical oxidation reaction of an ammonium persulfate salt. Next, a hydrophobic octadecyltrichlorosilane (OTS) self-assembled monolayer is formed by immersing the substrate into an OTS solution. Selective UV/ozone irradiation with a wavelength of 171 nm through a shadow mask can define the OTS SAM as surface hydroxyl groups on the PEN surface by breaking the chemical bond between the OTS and the hydroxyl group. The selective irradiation process induces the formation of distinct hydrophilic (OH) and hydrophobic (OTS) surfaces with a resolution of 60 μm. As a conducting ink, poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) is coated and self-aligned on the patterned arrays of the source/drain (S/D) electrodes of organic field-effect transistors (OFETs). Finally, using the recent widely used organic semiconductors such as poly(3-hexylthiophene), poly-[2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dionel-alt-thieno[3,2-b]thiophene], and poly{[N,N′bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)}, we demonstrate p-channel, n-channel, and ambipolar OFETs with a self-aligned PEDOT:PSS electrode of 50–100 μm channel length. All OFETs show a reasonably high and comparable field-effect mobility compared to identical devices with Au electrodes, and showed excellent mechanical stability in bending tests.