| Today's society has entered a core of the information industry to a knowledge-based economy era, Flat Panel Displays (FPDs) are playing important roles for mankind to get information and their effects are significant. Organic light-emitting devices (OLEDs) are important members of FPDs and attract world wide attention in the fields of science and industry due to their many merits of light weight, low cost, broad visual angle, high response speed, spontaneous light-emitting, high brightness and efficiency, etc. many progress have been made by the use of novel materials, suitable structures and the efforts of world-known companies, OLEDs are being moved out of the laboratory and made into commodities.But it is just the start to study on near-infrared (NIR) OLEDs. As to the near-infrared region relates to data storage, security markings, photodynamic therapy, biological detection, and optical-fiber communication, and other important areas of application, especially the military uses of Infrared detection, infrared guidance. Therefore the organic material electroluminescent device's Luminescence wavelength advance to the luminous near-infrared wavelength region is of great significance, but also of the considerable technical challenges. Up to now, 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 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 thesis, we have made some meaningful works relating to enhance the near-infrared intensity of CuPc in 1.1μm and the near-infrared emission mechanism of the devices.(1) We design the near-infrared organic Electroluminescence device basing on CuPc:器件A: ITO/ NPB(35nm)/ Alq3(32nm)/BCP(15nm)/ALQ(20nm)/AL器件B:ITO/ NPB(35nm)/ Alq3:CuPc(32nm)/BCP(15nm)/ Alq3 (20nm)/ALthe concentration of copper phthalocyanine is set to 10%, in order to compare with device B, device A was designed, the thickness of the device's the main thin film layer (hole-transport layer, light-emitting layer, Exciton barrier layer and electron-trasport Layer) and the total thickness of devices is the same, the only difference is that CuPc was doped into the ALQ of light-emitting layer in device B.the near-infrared emission in 1.1μm from device B was completed. by the analysis of the visible spectrum, near-infrared spectroscopy and current density - voltage curve of the devices, We conclude the near-infrared light emission mechanism of CuPc in device B: Forster energy transfer mechanisms and carrier trapping mechanisms play a major role; Both carrier trapping of CuPc and the forster energy transfer from Alq3 to CuPc induced to the near-infrared emission of CuPc and the decrease of Alq3's visible light. And the results show that using CuPc-doped Alq3 methods can be achieved the near-infrared emission of CuPc.(2)Basing on previous study, we continue to make in-depth research in CuPc, and put forward another approach to achieve CuPc's near-infrared emission: we utilized the overlap between the DCM PL spectrum and the Q band absorption spectra of the CuPc to complete the near-infrared emission of CuPc. We design the near-infrared organic Electroluminescence device basing on CuPc with a periodically arranged Alq3:CuPc/DCM multilayer structure.The device successfully achieved the near-infrared emission of CuPc in 1.1μm and improved the device near infrared emission intensity.To illustrate the reasons for the increasing the near-infrared emission intensity in device A and its energy transfer mechanism, we designed the following devices:Device A: ITO/NPB(35 nm) / Alq3 :CuPc(7 nm) /DCM (x=0.1 nm)/ Alq3 :CuPc(7 nm) /DCM (x=0.1 nm) / Alq3 :CuPc(7 nm) /DCM (x=0.1 nm)/ Alq3 :CuPc(7 nm) /DCM (x=0.1 nm)/ Alq3 (4 nm) /BCP (15 nm)/ Alq3 (20 nm)/Al Device B: ITO/NPB(35 nm) / Alq3 (7 nm) /DCM (x=0.1,0.3,0.5,0.7 nm)/ Alq3 (7 nm) /DCM (x=0.1,0.3,0.5,0.7 nm) / Alq3 (7 nm) /DCM (x=0.1,0.3,0.5,0.7 nm)/ Alq3 (7 nm) /DCM (x=0.1,0.3,0.5,0.7 nm)/ Alq3 (4 nm) /BCP (15 nm)/ Alq3 (20 nm)/Al,Device C: ITO/NPB (35 nm) / Alq3:CuPc (32 nm) /BCP (15 nm)/ Alq3 (20 nm)/Al,We conducted electrical performance testing of these Device, by comparison and Analysis, we found that:the near-infrared emission intensity for the device A increased by about 2.5 times corresponding to device C, while the visible light coming from Alq3 and DCM were weakened in device A, especially the visible light of DCM almost can not be observed.By the visible spectrum of the device and current density - voltage curve analysis, we conclude the near-infrared emission mechanism of CuPc in device A: in device A, forster energy transfer mechanisms play the most important role in the near-infrared emission of CuPc, carrier-trapping mechanisms and Dexter energy transfer mechanisms is secondary mechanism; DCM molecules acquire energy by carrier-trapping mechanisms and forster energy transfer mechanism from Alq3 to DCM, then the energy of DCM molecules transmitted to CuPc molecule by the forster energy transfer mechanism, and achieved the near-infrared emission of CuPc molecule in 1.1μm.(3) we investigated the optical (200 nm-2000 nm), electrical and electronic properties of indium-tin-oxide (ITO) (100 ?/□), ITO (12 ?/□), zinc-oxide (ZnO), Aluminum-doped ZnO (AZO) and polyaniline (PANI). We also fabricated 1.54μm NIR-OLEDs (near-infrared organic light-emitting diodes) based on Er(DBM)3Phen using ITO (100Ω/□), ITO (12Ω/□) and PANI as anodes, respectively. The devices structure were anodes/m-MTDATA (30 nm)/NPB (20 nm)/Er(DBM)3Phen (20 nm)/ Alq3 (30 nm)/Al. The results suggested that ITO (100Ω/□) which has a lower Sn content appear to be a relatively better choice for NIR-OLEDs emitting at about 1.54μm. we enhance the device's luminous efficiency and the device's output by improving Organic Electroluminescent Device electrode . |
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