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Polyethylene Imine as an Ideal Interlayer for Highly Efficient Inverted Polymer Light‐Emitting Diodes
Author(s) -
Kim YoungHoon,
Han TaeHee,
Cho Himchan,
Min SungYong,
Lee ChangLyoul,
Lee TaeWoo
Publication year - 2014
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.201304163
Subject(s) - materials science , work function , exciton , polymer , diode , optoelectronics , quenching (fluorescence) , luminous efficacy , electron , layer (electronics) , imine , chemical engineering , light emitting diode , photochemistry , nanotechnology , composite material , optics , organic chemistry , fluorescence , condensed matter physics , chemistry , physics , engineering , quantum mechanics , catalysis
Electron‐injecting interlayers (ILs) which are stable in air, inject electrons efficiently, block holes, and block quenching of excitons, are very important to realize efficient inverted polymer light‐emitting diodes (IPLEDs). Two air‐stable polymer electron‐injecting interlayers (ILs), branched polyethyleneimine (PEI) and polyethyleneimine ethoxylated (PEIE) for use in IPLEDs are introduced, and the roles of the ILs in IPLEDs comparing these with a conventional Cs 2 CO 3 IL are elucidated. These polymer ILs can reduce the electron injection barrier between ZnO and emitting layer by decreasing the work function (WF) of underlying ZnO, thereby effectively facilitating electron injection into the emitting layer. WF of ZnO covered by PEI is found to be lower than that covered by PEIE due to higher [N + ]/[C] ratio of PEI. Furthermore, they can block the quenching of excitons and increase the luminous efficiency of devices. Thus, IPLEDs with PEI IL of optimum thickness (8 nm) show current efficiency (13.5 cd A –1 ), which is dramatically higher than that of IPLEDs with a Cs 2 CO 3 IL (8 cd A ‐1 ).