Preparation Of P - Xylene Film And Its Application In Organic Electroluminescent Diode

A home-made Knudson Cell (KC) for parylene-N (PPXN) film formation is reported. By using PPXN buffer layers inserted at the anode-organic interfaces, current efficiency of organic light emitting diodes (OLED) based on tris (8-hydroxyquinolato) aluminum (Alq3) emitting layer was obviously improved. Also, PPXN buffers inserted in the electron transport layer result in current efficiency marked enhancement.1. Based on the molecular beam epitaxy (MBE) techniques, a home-made KC was special designed and prepared. By using the KC, PPXN films can be grown at a relative low reaction pressure of10-3Pa with rates of0.001-0.06nm/s. Growth rates of PPXN film can be accurately controlled by modulating the crucible temperature of the KC. PPXN films prepared were characterized by IR spectra, dielectric measurement and surface hydrophobicity.2. A PPXN buffer layer inserted between anode and organic layers in typical OLEDs based on N, N’-bis(naphthalene-1-yl)-N, N’-bis(phenyl) benzidine (NPB) and Alq3results in significant enhancement of the current efficiency. The enhancement can be1.7times higher compared to that of the buffer-free structure. Analyzing indicates the buffer plays a role of blocking the current of holes and electrons as well. Whether hole injection can be enhanced depends on electron accumulation at the buffer-organic interface. Inserting the PPXN buffer modifies carrier balance in the device, leading to the observed efficiency enhancement.3. Current efficiency in Alq3based typical organic light-emitting diodes is markedly improved by inserting a PPXN buffer layer in the Alq3layer. For an optimized structure with the PPXN buffer properly located, a current efficiency of42%higher than that of the control device is achieved. By using the light-emitting spectra of4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) doped Alq3(Alq3:DCM) strips to analyze the current variation, electron current enhancement is confirmed in PPXN inserted devices during operation, which leads to the observed efficiency improvement. The current evolution is explained by nonuniform potential distribution in the organic layer and the tunneling barrier reduction model.