title: Doping Evolution and Junction Formation in Stacked Cyanine Dye Light-Emitting Electrochemical Cells.
abstract: Cyanine dyes are fluorescent organic salts with intrinsic conductivity for ionic and electronic charges. Recently ( J. Am. Chem. Soc. 2013 , 135 , 18008 - 18011 ), these features have been exploited in cyanine light-emitting electrochemical cells (LECs). Here, we demonstrate that stacked, constant-voltage driven trimethine cyanine LECs with various counteranions develop a p-i-n junction that is composed of p- and n-doped zones and an intrinsic region where light-emission occurs. We introduce a method that combines spectral photocurrent response measurements with optical modeling and find that at maximum current the intrinsic region is centered at ∼37% away from the anode. Transient capacitance, photoluminescence and attenuance experiments indicate a device situation with a narrow p-doped region, an undoped region that occupies ∼72% of the dye layer thickness and an n-doped region with a maximum doping concentration of 0.08 dopant/cyanine molecule. Finally, we observe that during device relaxation the parent cyanines are not reformed. We ascribe this to irreversible reactions between doped cyanine radicals. For sterically conservative cyanine dyes, this suggests that undesired radical decomposition pathways limit the LEC long-term stability in general.
authors.affiliation: Laboratory for Functional Polymers, Empa, Swiss Federal Institute for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.|Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, EPFL , Station 12, CH-1015 Lausanne, Switzerland.
authors.forename: Sandra
authors.initials: S
authors.lastname: Jenatsch
authors.affiliation: Laboratory for Functional Polymers, Empa, Swiss Federal Institute for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.|Institute of Chemistry and Biological Chemistry, Zürich University of Applied Sciences , Einsiedlerstrasse 31, CH-8820 Wädenswil, Switzerland.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Laboratory for Functional Polymers, Empa, Swiss Federal Institute for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Matia
authors.initials: M
authors.lastname: Bulloni
authors.affiliation: Laboratory for Functional Polymers, Empa, Swiss Federal Institute for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Véron
authors.affiliation: Institute of Computational Physics, Zürich University of Applied Sciences , Technikumstrasse 9, CH-8401 Winterthur, Switzerland.|Fluxim AG , Technoparkstrasse 2, 8406 Winterthur, Switzerland.
authors.forename: Beat
authors.initials: B
authors.lastname: Ruhstaller
authors.affiliation: Fluxim AG , Technoparkstrasse 2, 8406 Winterthur, Switzerland.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Altazin
authors.affiliation: Laboratory for Functional Polymers, Empa, Swiss Federal Institute for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.|Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, EPFL , Station 12, CH-1015 Lausanne, Switzerland.
authors.forename: Frank
authors.initials: F
authors.lastname: Nüesch
authors.affiliation: Laboratory for Functional Polymers, Empa, Swiss Federal Institute for Materials Science and Technology , CH-8600 Dübendorf, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Hany
keywords: charge injection; cyanine dye; doping; intrinsic junction; light-emitting electrochemical cell