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Polymer Light‐Emitting Electrochemical Cells: Doping Concentration, Emission‐Zone Position, and Turn‐On Time
Author(s) -
Shin J.H.,
Robinson N. D.,
Xiao S.,
Edman L.
Publication year - 2007
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200600984
Subject(s) - dopant , materials science , doping , electrochemistry , electrode , analytical chemistry (journal) , optoelectronics , chemistry , organic chemistry
Direct optical probing of the doping progression and simultaneous recording of the current–time behavior allows the establishment of the position of the light‐emitting p–n junction, the doping concentrations in the p‐ and n‐type regions, and the turn‐on time for a number of planar light‐emitting electrochemical cells (LECs) with a 1 mm interelectrode gap. The position of the p–n junction in such LECs with Au electrodes contacting an active material mixture of poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐ p ‐phenylene vinylene) (MEH‐PPV), poly(ethylene oxide), and a XCF 3 SO 3 salt (X = Li, K, Rb) is dependent on the salt selection: for X = Li the p–n junction is positioned very close to the negative electrode, while for X = K, Rb it is significantly more centered in the interelectrode gap. Its is demonstrated that this results from that the p‐type doping concentration is independent of salt selection at ca. 2 × 10 20 cm –3 (ca. 0.1 dopants/MEH‐PPV repeat unit), while the n‐type doping concentration exhibits a strong dependence: for X = K it is ca. 5 × 10 20 cm –3 (ca. 0.2 dopants/repeat unit), for X = Rb it is ca. 9 × 10 20 cm –3 (ca. 0.4 dopants/repeat unit), and for X = Li it is ca. 3 × 10 21 cm –3 (ca. 1 dopants/repeat unit). Finally, it is shown that X = K, Rb devices exhibit significantly faster turn‐on times than X = Li devices, which is a consequence of a higher ionic conductivity in the former devices.