Based On The New Iridium Complexes (pbi) <sub> 2 </ Sub> Ir (acac) Phosphorescent Materials In Organic Light-emitting Devices

Organic light-emitting devices (OLEDs) have been attracted large volume of attraction due to its potential application in illumination source and display. However, currently there are also some shortcomings to prevent it from large scale commercial application such as high fabrication cost, low luminance efficiency and indistinct understanding about device mechanism. Aiming at those problems, some basic and systematic works have been performed to focus on the fabrication process to obtain high resolution device with passive matrix driving method and high efficiency phosphorescent OLEDs in this work.1. Using a novel type of phosphorescent iridium complexe of Materials bis(1,2-dipheny1-H-benzoimidazole)iridium(acetylacetonate) [(pbi)₂Ir(acac)], doped into the polymer host material poly(N-vinylcarbazole) (PVK) with low concentration in the emitting-layer. The devices with a structure of indium tin oxide (ITO)/PVK: (pbi)₂Ir(acac) (1 wt%)(70 nm)/bathocuproine(BCP)(x nm)/tris(8-hydroxyquinolate) aluminum (Alq₃) (30-x nm)/Mg:Ag (x is 30, 20, 10 and 0 nm) have been fabricated. Keeping the whole thickness of the hole blocking layer and electron transporting layer as a constant, the optimized device structure have been obtained, and the important factors for the improvement of devices performance have been investigated by adjusting the thickness of the hole blocking layer and electron transport layer between the emitting-layer and the cathode.2. High performance polymer light-emitting devices (PLEDs) based on a phosphor of noble metal complex (pbi)₂Ir(acac) doped into PVK host with various doping concentration were demonstrated. The photoluminescence (PL) and electroluminescen- ce (EL) spectra of PLEDs exhibited an emission intensity decrease of PVK and an gradually enhanced feature of (pbi)₂Ir(acac) with increased doping concentration. The devices performance was low at low doping concentration. Along with concentration increasing, the devices performance was enhanced, and the device with 5 wt% (pbi)₂Ir(acac) doped PVK system showed a high power efficiency of 3.84 lm/W and a luminance of 26,006 cd/m2. This result indicated that both energy transfer and charge trapping have a significant influence on the performance of PLEDs; continuing to increase the doping concentration, because of the quenching effect of phosphorescence materials device performance becomes much lower.3. White organic light-emitting devices (WOLEDs) have been fabricated by using a novel phosphorescence (pbi)₂Ir(acac) as sensitizer and a fluorescent dye of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) codoped into a carbazole polymer of PVK. Through characterizing the UV-Vis absorption spectra, the PL spectra of (pbi)₂Ir(acac), DCJTB and EL spectral properties of the WOLEDs, the energy transfer mechanisms of the codoped polymer system were discussed. The results demonstrated that the luminescent spectra with different intensity of (pbi)₂Ir(acac) and DCJTB were co-existent in the EL spectra of blended system. The efficient Farster and Dexter energy transfer between the host and guests enabled to obtain strong yellow emission from (pbi)₂Ir(acac) and DCJTB. With the blue emitting-layer of NPB, the codoped system device was achieved white emission. The device of codoped system showed the Commissions Internationale de 1'Eclairage (CIE) coordinates were more independent on the variation of bias voltage than that of phosphorescent doped PVK system.4. Using the ultra-thin layer of DCJTB, WOLEDs have been fabricated by using a novel phosphor of (pbi)₂Ir(acac) as a sensitizer doped into a carbazole polymer of PVK, and DCJTB as an ultrathin red light-emitting layer. The effect of ultrathin fluorescent light-emitting layer on the injection and transport characteristics of charge carrier and EL performance of polymer doped phosphor sensitized devices was discussed, and influential factors for the improvement of WOLEDs performance were investigated. The results demonstrated that the device exhibits stable EL spectra and CIE coordinates in a wide bias range. Both energy transfer and charge trapping play the role on the performance of WOLEDs.