The Preparation Of Diamond Film Used As OLED Field Emission Cathode

Due to its many advantages in display, the light-emitting devices has been researched in recent years, and it was expected to become the protagonist of the next generation of displays. But its practical application still exist some problems, such as efficiency, stability and efficiency, these three issues are strongly restricts the application of light emitting devices. The main topic is the low efficiency for electron injection, thereby causing imbalance of carrier recombination, resulting in low efficiency of light-emitting device, so the aim of this thesis is to improve the electron injection efficiency and luminous efficiency of the device. The traditional method is mainly focused on reducing barrier height between the cathode electrode and the organic layer to improve the electron injection efficiency, but this is a passive measure. The topics theory is based on the field emission and organic light-emitting, and a new cathode material-field emission film as cathode of the light emitting devices is used, and make the field emission electron injected into the organic layer in a mandatory way. It is different from the reported Field emission-Organic light-emitting device. The innovation of our device was we directly prepared organic light emitting devices on the field emission cathode, to avoid using of vacuum structure.Because of the diamond is a wide band gap semiconductor, and it has a negative electron affinity, which make it is easy for electron field emission, and can be obtain large area growth by CVD method, so we use diamond films as field emission cathode. Because the organic layer must be deposit on the diamond film directly, so it is required that the diamond film should be has good smoothness.Using microwave plasma chemical vapor deposition method prepared diamond films. By changing the deposition parameter, diamond films with different surface morphology were obtained. The surface roughness and their field emission properties were evaluated to identify the most suitable for use as field emission cathode of carbon membrane. Specific tasks are:1. Substrate pretreatment on the growth of diamond films:Adopt surface defect method to improve diamond nucleation rate, using different sizes of diamond grinding paste mechanical polishing substrates, comparing the diamond film grown on different substrates, found that after pretreatment by W5 diamond grinding paste, the substrate growth of diamond film have highest nucleation density, and can continuous film.2. The preparation of diamond films:Changing the deposition parameters, prepared with a cube, tetrahedral-shaped, spherical and triangular cone structure of the film, analyzed the formation mechanism of all kinds of crystal shape, and the field emission quality of samples which have smooth surface were tested, the results shown that the diamond film with triangle cone structure revealed the best emission performance.3. Nanocrystalline diamond thin films:Nanodiamond film with flat surface was grown, and carried on the field emission test, the film's opening field for 1.6 V/μm, at 4.2 V/μm the current density reached 900μA/cm2.4. New style flake nano-diamond film preparation:A flake nano-diamond film was prepared under high methane concentration, this type diamond film has high field enhancement factor for its unique surface morphology, the electric field current density reached 14.3mA/cm2 at 6.4V/um. Under low methane concentration, the higher plasma density also can promote the formation of flake nano-diamond, and can make the flake parting growth.5. Electroluminescence device fabrication:Contrast the characteristics of various diamond films, choose triangle cone structure diamond film and nanodiamond film as the OLED cathode prepared Diamond film/AlQ3/TPD/Ag structure device, and test the I-V characteristics of the device. Found using nanodiamond film as the cathode of OLED can improve the current efficiency, the highest current density was 360 mA/cm2, while the maximum current density of traditional glass substrate metal cathode device was 125 mA/cm2.