Polyelectrolyte-Mediated Electrochemical Fabrication of a Polyacetylene p−n Junction

Abstract

The diffusion of dopant counterions has made the formation of conjugated polymer p−n junctions challenging. We demonstrate polyelectrolyte mediated electrochemistry (PMEC) as a three-electrode technique for separately introducing n- and p-type regions in an ion-functionalized polyacetylene structure to form a p−n junction. PMEC uses a polyelectrolyte-based supporting electrolyte and ion-functionalized conjugated polymers to control the ions available for exchange between a solid sample and supporting electrolyte, and in this way, select for oxidative vs reductive electrochemical processes. A bilayer consisting of solid layers of anionically and cationically functionalized polyacetylenes was driven first to −1.5 V vs SCE and then to 0.6 V vs SCE using tetrabutylammonium polystyrene sulfonate/acetonitrile as a supporting electrolyte. The negative potential step n-doped the entire structure, and the positive potential step selectively p-doped the anionically functionalized layer to form a p−n junction as followed by spectroelectrochemistry and supported by current−voltage characterization. The polyacetylene p−n junctions were observed to exhibit diode behavior with ideality factors in the range of 3−3.5. Rectification ratios of greater than 500 at 1 V were achieved, and the junctions exhibited a small photovoltaic effect.