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Optimized Electrolyte Loading and Active Film Thickness for Sandwich Polymer Light‐Emitting Electrochemical Cells
Author(s) -
Diethelm Matthias,
Grossmann Quirin,
Schiller Andreas,
Knapp Evelyne,
Jenatsch Sandra,
Kawecki Maciej,
Nüesch Frank,
Hany Roland
Publication year - 2019
Publication title -
advanced optical materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.89
H-Index - 91
ISSN - 2195-1071
DOI - 10.1002/adom.201801278
Subject(s) - materials science , anode , cathode , electrolyte , absorption (acoustics) , active layer , doping , common emitter , polymer , diode , refractive index , electrochemistry , layer (electronics) , optoelectronics , oled , analytical chemistry (journal) , composite material , electrode , chemistry , thin film transistor , chromatography
Effects of ion concentration and active layer thickness play a critical role on the performance of light‐emitting electrochemical cells. Expanding on a pioneering materials system comprising the super yellow (SY) polymer and the electrolyte trimethylolpropane ethoxylate (TMPE)/Li + CF 3 SO 3 − , it is reported that a slightly lowered salt concentration and layer thickness result in a substantial efficiency increase, and that this increase is confined to a narrow concentration and thickness range. For a film thickness of 70 nm, a blend ratio SY:TMPE:Li + CF 3 SO 3 − = 1:0.075:0.0225, and a current of 7.7 mA cm −2 the current efficacy is 11.6 cd A −1 , on a par with SY light‐emitting diodes. The optimized salt content can be explained by increased exciton quenching at higher concentrations and hindered carrier injection and conduction at lower concentrations, while the optical dependence on the layer thickness is due to weak microcavity effects. A comprehensive optical modeling study is presented, which includes the doping‐induced changes of the refractive indices and self‐absorption losses due the emission–absorption overlap of intrinsic and doped SY. The analysis indicates either a thickness‐independent emitter position (EP) close to the anode or a thickness‐dependent EP, shifted to the cathode for increased thicknesses.