Investigation On The Interface Property And The Recombination Efficiency Of Organic Light-emitting Devices

Organic light-emitting devices(OLEDs) have attracted increasing attention in recent years because of their potential advantages。Nowadays researchers in this field throw themselves into exploiting high electroluminescence efficiency, stable luminescence materials and carrier transport materials, improving device architecture and otherwise. To get over the shortcomings of low efficiency, short life and unstable properties of Organic electroluminescence devices, In contrast to the rapid progresses made in the experimental front, systematic and comprehensive understanding of the property of interface and recombination efficiency involved in about OLEDs is important in theory and utility.Based on the research results of other groups, the main results about the carrier injection,transport and recombination especially the performance of interface are listed as following:1. By applying the model of interface between metal and inorganic semiconductor to that of the metal and organic semicondonduct, the numerical value calculation is present. We discuss the influences of the atom distance of interface and the density of chemical bond on the interface dipole energy,analyze the reason why interface field intensity changes with the chemical bond. We also give a reasonable comprehension of inherent relation between the interface dipole energy and work function of the metal.2. A multilayer structure ITO/TPD/Alq/LiF/Al has been presented to calculate the J-V dependence of organic electroluminescent devices (OELDs). After detailed numerical calculation we know: 1) The additional dipole energy introduced by inserting a thin LiF layer at metal/organic interface significantly decreases the potential barrier for electrons injection and the turn-on voltage of OELDs; 2) Too thick or too thin LiF will increase the turn-on voltage of OELD and decrease its performance. It has been found that the optimal thickness of inserted LiF should be in the range of 1.5~5.0nm. We can verify that this model is proper to explain the performance enhancement of OELDs via modification of electrode with LiF.3. With the assumption of injection limited of cathode and Ohm contact of anode, ignoreing the electron leakage current, A bilayer model has been proposed to calculate the recombination efficency and recombination zone width of the devices. As a result: The change of device structure leads to the redistribution of the electric intensity. Keeping the total thickness of the device and increasing that of hole transport layer result in larger electron injection and narrower recombination zone width.So does the recombination rise.