Study on Organic Near-infrared Light-emitting Devices Based on Phthalocyanines

Study on Organic Near-infrared Light-emitting Devices Based on Phthalocyanines
　　Nowadays,the technique of informations displays is the most important means for mankind obtaining information and the technique of organic light-emitting displays attract wide attention as an important member of Flat Panel Displays..In addition ,near-infrared region are widely used in some areas such as the optical communication ,data storage and infrared detection. Nowdays ,the semiconductor lasers based on inorganic material such as third and fifth Ball Neodymium Magnets group compound play an important part in the optical communication. As is known to all, many of these compounds have some toxicity and the fabrication technology of traditionary semiconductor laser is very difficult and the equipments are also dear and the requirement for the purity of the materials is very high.Organic compounds have many excellences such as the easy fabrication technology ,the cheap cost and being able to bend,so many scientists pay importat attention to the organic compounds. Because the main windows of optical communication which lie in 850 nm, 1330 nm, 1550 nm are in near-infrared region. Therefore, to develop low cost and no pollutig organic materials with near-infrared light emitting has potential value for regions like optical communication.Recently most of the organic electroluminescence (EL) materials in the NIR region reported were organic complexes with trivalent rare earth ions such as Er3+, Nd3+, Pr3+, Tm3+,Yb3+. Only few organic materials containing no rare earth ions showed EL characteristic at wavelengths longer than 1μm.But complexes with rare earth ions have some disadvantages.
　　The EL originate from the f-f transition of rare earth ions which is a parity-forbidden process. In addition,the organic light emitting diodes have very low EL efficiency ,because the bandgap of organic ligands is normally large which result in the low effective injection of carriers into organic ligands .To develop organic materials containing no rare earth ions is very important to near-infrared light emitting. Phthalocyanines are the topic which people have studied for about one hundred years..People have synthesized more than 10000 kinds of phthalocyanine derivatives ,which are used in many regions like communication. and so on..Theπconjugated http://www.chinamagnets.biz/ system of phthalocyanines are important in near-infrared light emitting.CuPc is widely used in OLED,which is often used as hole-inject layers.We have fabricated doped and undoped devices with CuPc.First we fabricated undoped devices whose structure is ITO/NPB/CuPc/BCP/Alq3/ Al.There is a weak emitting peak around 1.1μm. Then we develop the structure of the devices and fabricated the alternate devices whose structure isITO/NPB/CuPc/Alq3/....../ CuPc/ Alq3/Al.There is a emitting peak round1.1μm which is stronger than the first one device and this demonstrated the efficiency of energy transfer is enhanced .Then we fabricated the devices employing CuPc doped into CBP. The structure is ITO/NPB/CBP: CuPc/BCP/Alq3 /Al and there is a strong emitting peak round 1.1μm .We change the concentration of CuPc doped into CBP and fabricated devices with different concentration (0 wt% 6 wt% 12 wt% and 20 wt%).The intensity of emitting peak varied with the change of the concentration . 12wt% is optimal and when the concentration is increased,the intensity would be weaker. In the UV-Visible EL spectrum of devices,there is a blue emitting peak which come from NPB. With the concentration of CuPc is increased,the intensity of blue emitting light would be weaker.
　　In the figure of current-voltage characteristics, In the case of lower doping concentrations (≤12 wt %) the driving voltages of doped devices were higher than that of undoped devices. When the doping concentrations were higher than 12 wt% direct hole injection from NPB into CuPc and direct electron injection from BCP into CuPc may lead to the lower driving voltage.These demonstrated that the direct charge trapping process is important and Forster and Dexter energy transfer play a minor role in whole process. This kind of devices are important to near-infrared light emitting diodes. In order to study the effect on the emitting wavelength of phthalocyanines and on the intensity of emitting peak,we have synthesized substituted phthalocyanines according to the molecule structure of CuPc and H2Pc,i.e. (4-thymol)CuPc and(4-tert)H2Pc.We purified the materials.Then we tested PL spectrum of (4-thymol)CuPc under 300K. The films of (4-thymol)CuPc were deposited in vacuum .There was only a emitting peak round 1150 nm.We fabricated devices employing (4-thymol)CuPc whose structure is ITO/NPB/ (4-thymol)CuPc /Alq3 /Al .There is a emitting peak round 1.1 urn whose position is near that of the devises based on common CuPc.Then we fabricated the organic light http://www.chinamagnets.biz/ emitting devices based on (4-tert)H2Pc doped into CBP,whose structure is ITO/NPB/CBP:(4-tert)H2Pc/BCP/Alq3/Al. We fabricated devices with different concentration(20 wt%, 40 wt% 80 wt% and 100 wt%).Throughtesting the near-infrared spectrum,we found there was a emitting peak round 910 nm for the devices,the intensity of emitting peak decreased with the increase of the concentration.In addition,we have synthesized novel three-nuclear PcZn.Bu we fail to purify the materials,so there is 2,3-tetra-(2-iPr-5-Me)PcZn in the materials.We spin cost the mixture of PVK and the materials on quartz slice and through testing ,we found there was a strong emitting peak round 900 nm .Then we fabricated the devices employing the materials.We tested the near-infrared characteritcs,and found the emitting peak lied round 900 nm ,which is compatible with PL spectrum.but we can not confirm which material is relate to the peak and this requires the further study.