Study on external quantum efficiency and lifetime of white organic light-emitting devices
Date Issued
2012
Date
2012
Author(s)
Lin, Bo-Yen
Abstract
In this thesis, we study the external quantum efficiency (EQE) of different measurement methods, operational half-lifetime of OLEDs, and the design of a high efficiency and high color stability WOLEDs.
In chapter 3, a stable OLED was made of N,N’-di(1-naphthyl)-N,N’-diphenyl-benzidine (NPB) as hole transport layer (HTL) and tris(8-hydroxyquinolinato) aluminium (Alq3) as the electron transport layer (ETL) and emitting layer (EML) to measure the EQE of such device via integral sphere and view angle spectra measurements. A factor existed between EQE of integral sphere and of view angle spectra, which is about 1.22. The difference is due to uncertainty of large view angle spectra measurement. The uncertainty was originated from the out of focus in large view angle.
In chapter 4, a high efficiency and high color stability WOLED was demonstrated via blue double emitting layer (DEML) co-doping red and green dopant with optimized doping concentration and doping position. The WOLED exhibited peak current efficiency of 29.9 lm/w (5.84 nit), EQE of 13.23%. The CIE coordinates shift from 100 nit to 10000 nit was only (0.0079, 0.0092). A common problem existed in multi-layer WOLEDs was overcome via the design of EML.
In chapter 5, a sequence of OLED including monochromatic, dichromatic, and trichromatic devices were fabricated to investigate the lifetime and discussed the degradation. The half-life time of OLEDs could be enhanced by employing DEML in device structure or doping the more stable organic material to reduce the degradation of unstable blue phosphorescent material. A WOLED using blue DEML structure with long half-lifetime of 50 hrs at driving current density of 2.5 mA/cm2 was realized.
Subjects
White organic light emitting
lifetime
external quantum efficiency
co-doping
Type
thesis
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