Solvato-Controlled Doping of Conducting Polymers: Enhanced Stabilty in Silver-Triflate Doped Films
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P3AT films doped with the AuC14-[2] or bis(trifluoromethanesulfonyl)imide[3] anions exhibit lifetimes much greater than their FeCI4 doped counterparts; additionally, polythiophenes which are 3- or 3,4-substituted with electron releasing alkoxy groups have lower oxidation potentials and longer lifetimes.[4] In this report, we describe (i) the stabilization of polymer/dopant solutions with dopantcoordinating ligands (ii) casting of the solutions described in (i) and evaporation of the coordinating ligand, yielding stable, conductive, silver-containing films doped with the triflate anion (iii) electrochemical oxidation of P3AT films (in the presence of the triflate anion) at various potentials and determination of their half-lifetimes (for comparison to silver triflate doped films). This work is part of a research program into the photolithography of electronically conducting polymers in which the stability and processability of the conducting polymer are important issues.[5] EXPERIMENT Regioregular poly(3-hexylthiophene) (P3HT) and poly(3-dodecylthiophene) (P3DDT) were prepared by a literature procedure.[6] Silver triflate (AgOTf (Sigma Chemical Co.), acetonitrile (Caledon, HPLC grade), lithium triflate (LiOTf) and tetrabutylammonium tetrafluoroborate (Aldrich) were used without further purification. Pyridine (BDH) was dried over KOH and distilled prior to use. Chloroform (Mallinkrodt, reagent grade) was dried over 341 Mat. Res. Soc. Symp. Proc. Vol. 488 01998 Materials Research Society
calcium hydride and distilled before use. Diethyl ether (Caledon, reagent grade) was distilled from sodium. Tin-doped indium oxide (ITO) coated glass slides were obtained from Delta Technologies. UV/vis spectra were recorded on a Cary 3E spectrophotometer, NIR spectra were recorded on a Bomem MB-Series spectrometer. Electrochemical measurements were recorded using an EG&G Model 173 Potentiostat/Galvanostat, Fluke 8840A and 8000A digital multimeters, and a co-linear four-point probe. Film thickness measurements were recorded with a Tencor Alpha Step 100 profilometer. In-situ conductivity measurements of electrochemically doped P3HT were recorded in 0.1M LiOTf/acetonitrile solutions using a platinum double-band electrode[7] and methods reported in literature.[8,9,10] Measurements of the electrochemical potentials of chemically doped films were performed in a 0.1M chloroform solution of tetrabutylammonium tetrafluoroborate, using an ITO slide as the working electrode, and Ag/AgC1 as the reference. For lifetime measurements of electrochemically doped P3HT films, ITO-coated glass slides were masked with resist and etched in a 6 M HCI solution (Anachemia, reagent grade) containing 0.2 M FeC13 (BDH)[1 1] for 20 minutes to give two-I cm 2 ITO pads separated by a 0.7 mm gap. Wires were attached to each pad with Electrodag (Acheson Colloids Canada Ltd.) and insulated with 5 minute epoxy. P3HT was spin cast from chloroform. Each assembly was oxidized at a constant potential in a 0.1M LiOTf/acetonitrile solution until a constant current was att
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