How To Improve The Luminance Efficiency Of Fluorescent OLED Devices With Different Structures

ABSTRACT:In this paper, OLEDs of all kinds of structures are researched to improve their electrical properties and current efficiency.1. for devices of multi-layer structure:a) Organic-inorganic composite devices ITO/MEHPPV(-70nm)/ZnS(20nm)/Al was prepared. Compared with the monolayer device ITO/MEHPPV(-70nm)/Al, the spectral red shift and broadening towards the long-wavelength direction in the EL of bilayer devices are observed, due to the exciplex emission in bilayer devices. The current efficiency of organic-inorganic composite device is not higher than that of device ITO/MEHPPV(-70nm)/BCP (20nm)/Al, but the turn-on voltage has been lower3V;b) For the poor compatibility of interface of organic and inorganic, using the UV ozone treatment onto molybdenum oxide near to anode, the carrier injection efficiency of the device ITO/MoO3(5nm)/MEH-PPV/A1has been improved;c) By inserting5nm of Au layer between MoO3and TPD near to anode, forming a small trap for holes, reducing the current density in the device, the current efficiency of device ITO/MoO3(5nm)/TPD/Alq/LiF/Al has been improved;d) Taking exciplex luminous of NPB:TphNI as an indicator, prepared the three-layer device ITO/NPB/NPB:TPhNI (1:1)/TPhNI./LiQ/Al, keep the luminescence area away from two electrodes and are controlled at the middle position of the device, EL spectra does not change with the voltage. Stability of the chromaticity has been improved, and so the current efficiency, compare to the double and single devices with the same luminescent layer.2. for devices of tandem structure:a) By adding semi-transparent Au/Al layer as anode, the narrowing of EL spectra was discussed, and the reason is the "selected pass" of light-transmissivity in Au thin layer;b) By cautiously designing an evaporation mask, tandem OLED consisting of three electrodes and two independent light-emitting units was successfully prepared(ITO/TPD/AlQ:DCJTB(5%)/LiF/Al/Au/TPD/AlQ/LiF/Al). The translucent Al/Au intermediate electrode can be drawn forth and act as cathode and anode. The emission color of this OLED can be controlled by the applied bias. The voltage of the entire device is approximately equals to the sum of units R and G when the current densities are the same. The current efficiency of the entire device is several folds larger than the sum of two components at the same current density. The source of higher current efficiency can be attributed to the charge-generating of the Al/Au intermediate electrode. Besides connecting light-emitting units in series, this kind of intermediate electrode can also generate charge and improve the current efficiency of the tandem OLED, provides an experimental basis for preparation of controllable emission color and high-efficiency OLED.3. for devices of single-layer structure:a) The efficiency of the single-layer device was improved by thermal annealing while applying an electric field to MEH-PPV thin film;b) Prepared doping system of PVK:TPB, PVK:C545T, PVK:Rubrene and PVK: DCJTB, found that the lifetime of delayed fluorescence depends on the gap between the HOMO of host and dopant materials, so as the gap between the LUMO of host and dopant materials, the smaller the ΔELUMO and ΔELUMO are, the shorter the lifetime of delayed fluorescence are, the higher the current efficiency are.