title: Time-Resolved Chemical Mapping in Light-Emitting Electrochemical Cells.
abstract: An understanding of the doping and ion distributions in light-emitting electrochemical cells (LECs) is required to approach a realistic conduction model which can precisely explain the electrochemical reactions, p-n junction formation, and ion dynamics in the active layer and to provide relevant information about LECs for systematic improvement of function and manufacture. Here, Fourier-transform infrared (FTIR) microscopy is used to monitor anion density profile and polymer structure in situ and for time-resolved mapping of electrochemical doping in an LEC under bias. The results are in very good agreement with the electrochemical doping model with respect to ion redistribution and formation of a dynamic p-n junction in the active layer. We also physically slow ions by decreasing the working temperature and study frozen-junction formation and immobilization of ions in a fixed-junction LEC device by FTIR imaging. The obtained results show irreversibility of the ion redistribution and polymer doping in a fixed-junction device. In addition, we demonstrate that infrared microscopy is a useful tool for in situ characterization of electroactive organic materials.
authors.affiliation: Division of Molecular Physics, Department of Physics, Chemistry and Biology, Linköping University , Linköping SE-581 83, Sweden.
authors.forename: Mohammad Javad
authors.initials: MJ
authors.lastname: Jafari
authors.affiliation: Department of Science and Technology, Campus Norrköping, Linköping University , Norrköping SE-601 74, Sweden.
authors.forename: Jiang
authors.identifier: http://orcid.org/0000-0002-6291-1307
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Science and Technology, Campus Norrköping, Linköping University , Norrköping SE-601 74, Sweden.
authors.forename: Isak
authors.initials: I
authors.lastname: Engquist
authors.affiliation: Division of Molecular Physics, Department of Physics, Chemistry and Biology, Linköping University , Linköping SE-581 83, Sweden.
authors.forename: Thomas
authors.identifier: http://orcid.org/0000-0002-1639-5735
authors.initials: T
authors.lastname: Ederth
keywords: FTIR spectroscopic imaging; doping profile; dynamic p−n junction; electrochemical doping; infrared microspectroscopy; ion distribution; light-emitting electrochemical cell; principal component analysis