Analysis of the Electrical Properties of an Electron Injection Layer in Alq(3)-Based Organic Light Emitting Diodes

Abstract

We investigated the carrier transfer and luminescence characteristics of organic light emitting diodes (OLEDs) with structure ITO/HAT-CN/NPB/Alq(3)/Al, ITO/HAT-CN/NPB/Alq(3)/Liq/Al, and ITO/HAT-CN/NPB/Alq(3)/LiF/Al. The performance of the OLED device is improved by inserting an electron injection layer (EIL), which induces lowering of the electron injection barrier. We also investigated the electrical transport behaviors of p-Si/Alq(3)/Al, p-Si/Alq(3)/Liq/Al, and p-Si/Alq(3)/LiF/Al Schottky diodes, by using current-voltage (I-V) and capacitance-voltage (C-V) characterization methods. The parameters of diode quality factor n and barrier height phi(b) were dependent on the interlayer materials between Alq(3) and Al. The barrier heights phi(b) were 0.59, 0.49, and 0.45 eV, respectively, and the diode quality factors n were 1.34, 1.31, and 1.30, respectively, obtained from the I-V characteristics. The built in potentials V-bi were 0.41, 0.42, and 0.42 eV, respectively, obtained from the C-V characteristics. In this experiment, Liq and LiF thin film layers improved the carrier transport behaviors by increasing electron injection from Al to Alq(3), and the LiF schottky diode showed better I-V performance than the Liq schottky diode. We confirmed that a Liq or LiF thin film inter-layer governs electron and hole transport at the Al/Alq(3) interface, and has an important role in determining the electrical properties of OLED devices.