Electronic Device Characteristics and Charge Conduction Mechanisms of Single-Layer Organic Light Emitting Devices Based on Alq_3, TPD:Alq_3 and TPD:PBD:Alq_3 Blend System

摘要

Three single layer OLED devices which are ITO/PEDOT:PSS/Alq_3/AI, ITO/PEDOT:PSS/TPD:Alq_3/AI and ITO/PEDOT:PSS/TPD:PBD:Alq_3/AI have been fabricated. The thickness of pure thin film of Alq_3, and blended thin films of TPD:Alq_3 and TPD:PBD:Alq_3 which form the emission layer of the single layer OLED devices is 80 nm. Structural properties of Alq_3, TPD:Alq_3 and TPD:PBD:Alq_3 thin films were characterized by Fourier Transform Infrared (FTIR) and X-Ray diffraction (XRD). The FTIR spectrum of TPD:PBD:Alq_3 blend shows significant overlap from each vibration mode of TPD, PBD and Alq_3 molecules. It is found that a broad diffraction hump located at around 2θ ≈ 25° in the XRD spectra, indicating that all pure and blends materials have formed amorphous thin films. The electronics parameters such as ideality factor n, barrier height Φ_b, saturation current, I_o and series resistance R_s are extracted from the conventional In I-V, Cheung's functions and Fowler Nordheim (FN) function. The trend of the evaluated parameters calculated from Cheung's and Fowler Nordheim (FN) methods are found to be consistent with those calculated from the conventional I-V method. In the double logarithmic I-V plots, three distinct regions based on the slope of the plots have been identified and the transport mechanisms are discussed and explained.