[Multiple emissions in organic electroluminescent device using a mixed layer as an emitter].
A organic electroluminescent device has been fabricated by using a mixed layer as an emitter. The configuration of the device is ITO/TPD/TPD: PBD(equimole)/PBD/A1, in which TPD (N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine) and PBD (2-(4'-biphenyl)-5-(4''-tert-butylphenyl)-1,3,4-oxadiazole) are used as hole transport material and electron transport material, respectively. Broad and red-shifted electroluminescent spectra related to the fluorescence of constituent materials were observed. It is suggested that the monomer, exciplex and electroplex emissions are simultaneously involved in EL spectra by comparison of the EL with the PL spectra and decomposition of the EL spectrum. The type of exciplex is the interaction between the excited state TPD (TPD*) and PBD in the ground state, and the type of electroplex is a (D+-A-)* complex by cross-recombination of hole on the charged hole transport molecule (D+) and electron on the charged electron transport molecule (A-). All types of excited states show different formation mechanisms and recombination processes under electric field. The change of emission strengths from monomer and excited complexes lead to a blue-shift of the emissive spectra with an increasing electric field. The maximum luminance and external quantum efficiency of this device are 240 cd x (cm2)(-1) and 0.49%, respectively. The emissions from exciplex or electroplex formation at the organic solid interface generally present a broad and red-shifted emissive band, providing an effective method for tuning of emission color in organic electroluminescent devices.
Zhu
Wen-qing
WQ
Department of Materials, Shanghai University, Shanghai, China.
Wu
You-zhi
YZ
Zheng
Xin-you
XY
Jiang
Xue-yin
XY
Zhang
Zhi-lin
ZL
Sun
Run-guang
RG
Xu
Shao-hong
SH
D001713:Biphenyl Compounds / Q000737:chemistry; D055664:Electrochemical Techniques / Q000295:instrumentation / Q000379:methods*; D004735:Energy Transfer; D005453:Fluorescence; D049408:Luminescent Agents / Q000737:chemistry*; D008163:Luminescent Measurements / Q000295:instrumentation / Q000379:methods*; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D010069:Oxadiazoles / Q000737:chemistry; D015203:Reproducibility of Results
C549860:2-(4'-biphenyl)-5-(4''-tert-butylphenyl)-1,3,4-oxadiazole; D001713:Biphenyl Compounds; D049408:Luminescent Agents; C549859:N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine; D009930:Organic Chemicals; D010069:Oxadiazoles