The Study On Organic Near-infrared Light-emitting Materials And Devices

Since C.W. Tang has reported high brightness organic light-emitting devices (OLEDs) with low operating voltage for the first time in 1987, OLEDs have received more and more attentions. OLEDs have many merits such as: light weight, thin thickness, low cost, broad visual angle, fast response speed, active emitting, low energy consume, high brightness and efficiency, broad operating temperature, more choice of materials, availability for full color display and flexible display, etc. Owing to the research on new materials, optimization of device structure and improvement of fabrication processes, OLEDs have developed rapidly. So far, red and green monochromatic devices have been commercially available, but it is just the start to study on near-infrared (NIR) OLEDs. Most efforts have been focused on metal-organic complexes based on several trivalent rare earth ions like, e.g., erbium (Er3+), neodymium (Nd3+) or praseodymium (Pr3+). Only a few organic materials containing no rare earth ions have shown EL characteristic at wavelengths longer than 1μm. There is a substantial problem as regards the emitting quantum efficiency because of the following reasons: i) The EL originate from the f–f transition of rare earth ions, which is a parity-forbidden process. ii) The NIR emission was near-field deactivation by the host associated with coupling of the optically excited state to the vibrations (such as O-H and C-H et al.) of the organic molecule or polymer. iii) The ligand-sensitization scheme observed for the optical excitation of the organic ligands has not been confirmed to occur in current excitation. To realize the ligand-sensitization scheme in the current excitation, carriers must be injected into the HOMO and LUMO of organic ligands. Since the bandgap of organic ligands is normally large, the effective injection of carriers into organic ligands is difficult to achieve and so the EL efficiency thus generated becomes low. To search organic infrared emissive materials containing no rare earth ions has become a new challenge.In this dissertation, we have fabricated NIR-OLEDs employing the copper phthalocyanine (CuPc) doped into 4,4′-N,N′-dicarbazole-biphenyl (CBP). Room-temperature electrophosphorescence was observed at about 1.1μm due to the T1 - S0 transition of the CuPc. There exists very weak emission of CBP from undoped devices. In the case of lower doping concentrations (<12 wt %) the driving voltages of doped devices were higher than that of undoped devices. The results indicate that F?rster and Dexter energy transfer play a minor role in these devices, and direct charge trapping followed by electron-hole recombination on the emitter appears to be the dominated mechanism.We have synthesized a serial of metal-organic complex based on copper. These complex have been characterized and analyzed by UV-Vis-NIR absorption spectrum and PL spectrum. Cu ( DBM ) 2 and [Cu(μ-4 ,4'-bipy)(BF4)]n found to have property of NIR PL.Three kinds of sandwich-type erbium phthalocyanines with different symmetry have been synthesized and characterized by TOF-MS, UV-Vis-NIR absorption spectrum and PL. It has been found that the emission intensity of 1550 nm was increased with the increasing of the molecular structuce asymmetry.Zn(DBM)₂ and In(DBM)₃ have also been synthesized and characterized by UV-Vis absorption spectrum and PL spectrum. We have fabricated PLED employing the two materials doped into PVK. The devices structure were ITO/PVK:Zn(DBM)(250nm)/BCP(10nm)/Alq(330nm)/ Al and ITO/PVK:In(DBM)₃(50nm)/BCP(10nm)/Alq₃(30nm)/ Al.