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Quantum dot light‐emitting diode using 2,2′‐bis(N‐carbazolyl)‐9,9′‐spirobifluorene as a morphologically and thermally stable hole‐transporting material
Author(s) -
Tsuzuki Toshimitsu,
Motomura Genichi,
Yamamoto Toshihiro
Publication year - 2016
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201600270
Subject(s) - quantum dot , materials science , light emitting diode , optoelectronics , diode , thin film , electroluminescence , nanotechnology , layer (electronics)
We investigated the morphology of vacuum‐deposited films of hole‐transporting materials 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP) and 2,2′‐bis(N‐carbazolyl)‐9,9′‐spirobifluorene (CFL) on a colloidal quantum dot (QD) film by atomic force microscopy (AFM) and fabricated quantum dot light‐emitting diodes (QD‐LEDs) using CBP and CFL. Surface free energy of the QD film is lower than those of CFL and CBP. Low surface free energy of the QD film affects the wetting property of materials deposited on the QD film. From the AFM images, 3D island growth was observed in the CBP film, whereas planar growth was observed in the CFL film. We consider that the large molecular mass and the molecular shape of CFL with the perpendicular arrangement of the two bulky π‐electron systems restrain the rearrangement of the molecules during vacuum deposition. The QD‐LEDs using CBP or CFL as a hole‐transporting material showed saturated green emission. Luminance of the QD‐LED using CFL was higher than that of the QD‐LED using CBP at high voltages. This resulted from thermal stability of the CFL. The external quantum efficiency of the QD‐LED using CFL was 3.3% and was higher than that of the QD‐LED using CBP because the CFL formed the smooth film on the QD film.