A Conjugated Polymer pn Junction

Abstract

Dopant counterion diffusion has made the conjugated polymer pn homojunction a challenging target for decades. We report the electrochemical fabrication of a polyacetylene pn homojunction based on internally compensated forms where the dopant counterions are covalently bound to the polymer backbone. After drying under vacuum, the pn junction exhibits diode behavior with the ratio of the forward to reverse current at 2 V being 7. Despite such modest diode behavior, the fabricated pn junction is significant because it demonstrates the utility of internal compensation in the fabrication of metastable interfaces between dissimilarly doped conjugated polymers.

Recent Applications of Conjugated Polyelectrolytes in Optoelectronic Devices

“…Bilayer mixed ionic-electronic conductors (MIECs) composed of poly ((2-cyclooctatetraenylethyl)-trimethylammonium trifluoromethanesulfonate) (P16) and poly-(tetramethylammonium 2-cyclooctatetraenylethanesulfonate) (P17)(Scheme 4) sandwiched by Au electrodes were presented by Cheng et al [90,91] Unlike conventional PLECs these MIEC bilayer devices display significant rectification. Bilayer MIECs fabricated from P17 and poly((2-cyclooctatetraenylethyl) trimethylammonium trifluoromethanesulfonate) (P18)(Scheme 4) were immersed in CH 2 Cl 2 , a bias was applied, and charge was injected.…”

“…[91] A frozen p-i-n junction was thereby established in which the ions were not mobile. Such studies may provide a strategy to fabricate frozen junction PLECs, which are highly desirable due to their reduced response time and improved stability.…”

On-demand photochemical stabilization of doping in light-emitting electrochemical cells

“…[28,29] The p-n junction is built at a temperature at which the ions are mobile, and the device is thereafter cooled to a temperature at which the ions effectively become immobile and the p-n junction as a consequence is stabilized. [30][31][32][33][34][35][36] Lonergan and co-workers stabilized a p-n junction at the interface between a cationic and an anionic conjugated polyelectrolyte by solvent-induced removal of the mobile counter-ions, [37] while Bazan et al utilized in-situ boron-fluoride chemistry on a similar device structure for the same purpose. [38] Finally, Leger and Bartholomew [39] conceptualized the more generic "chemical stabilization" approach, which utilizes designed dopant counter-ions that can be physically immobilized via cross-linking polymerization reactions that presumably are initiated by electrochemical means.…”

Organic Electronics: The Ions Have It

“…[21][22][23][24] Several methods for achieving such a fixed junction have been demonstrated to date; the first report took advantage of the temperature-dependent ionic mobility in the solid-state film. After a desired ion distribution is obtained in this system, the temperature of the device is reduced to a point where the ions are no longer mobile.…”

“…Using this technique, layered structures are used with positively charged pendants along one electrode and negatively charged pendants along the other. The counterions to the pendants are then either removed from the system through solvent-soaking, [22] or allowed to remain in the system. [23] Finally, building polymerizable groups on to an ionic species, followed by immobilizing the counterions via covalent bond formation in situ, provides a simple method for creating a fixed polymer junction that is compatible with large-scale processing techniques.…”