Interface Effect Of The Organic Electroluminescent Devices Impact On Device Performance

Although the breakthrough of the research and development oforganic light-emitting diodes(OLED) has been gained in last 20 years,some major basic problems remain ambiguous, which lead to shortlifetime and low efficiency of devices. In order to solve a series ofproblems, it should intensify the understanding of luminescencemechanism and the performance of thin film organic materials, transportcharacteristics of carriers of thin film materials, degradation mechanismof devices, interfacial characteristics of devices and interfacesengineering. The numerical simulation was performed mainlysurrounding the metal/organic semiconductor interface, metal/inorganic/organic semiconductor interface and organic/organic semiconductorinterface in this paper.The insulating buffer layer modification of the metal/organicinterface has been one of the effective ways to improve the carrierinjection of OLED. An analytical model to calculate electroluminescence(EL) efficiency of bilayer organic light-emitting devices, considering theinfluence of introducing LiF insulating buffer layer at metal/organicinterface on the barrier height for electrons injection, was presented. Therelations of EL efficiency versus applied voltage, injection barrier,internal interfacial barrier and the thickness of organic layer werediscussed, the J-V characteristics of OLED inserting LiF buffer layers ofdifferent thickness were simulated successfully, the optimal thickness ofLiF buffer layer was achieved. By comparing with the experimentalresults, the validity of predictions from this model was tested. These willbe conducive to the selection and the optimal thickness design of bufferlayer material.The organic/organic semiconductor interracial characteristics ofOLED control the transport of carriers between layers and the region ofthe device where recombination takes place. In the light of thisbackground, a disordered hopping model of charge carriers at theorganic/organic interface in bilayer organic light-emitting diodes waspresented. The calculated results indicate that the distribution of electron and hole densities is determined by the effective barrier height at theorganic/organic interface, at the same time, the field strength isdetermined by the distribution of electron and hole densities. Then weanalyzed the influences of the variation of electric field, barrier heightand efficient hopping distance in OLED on recombination efficiency.This model might explain the relative experimental phenomena.The delay time is an important index of performance evaluation inOLED. Based on the physics mechanism of injection, transport andrecombination of the charge carriers, a model was developed to calculatethe delay time of electroluminescence (EL) from bilayer organic lightemitting diodes. The effect of injection, transport and recombinationprocess on the EL delay time was discussed, possible explanations weregiven. A ground of recombination or EL delay time versus appliedvoltage curves with different internal interface barrier, the built-inpotential and the thickness of hole transport layer are listed, we found thatthe effect of the internal interface barrier and the built-in potential holdthe upper hand over the thickness of hole transport layer. It has a certainreferenced meaning to respond rapidly to the functional materials andstructure options of EL devices.