The effect of thickness of light emitting layer on physical properties of OLED devices

Abstract

In this work, we performed to study the effect of thickness (35, 55, 75 and 95 nm) of the light emitted layer (EML) on physical properties of organic light-emitting diode (OLED) devices. We used indium tin oxide (ITO) for the anode in OLED. The ITO substrates were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and optical absorption (UV–vis). X-ray diffraction studies showed that the ITO films were polycrystalline with a hexagonal or wurtzite structure of indium oxide In2O3. Atomic force microscopy analysis demonstrated that the value of surface roughness ITO is an acceptable value for the proper transfer of the carriers from the boundary of the layers. Optical transmittance spectra of the ITO film showed high transparency of about ∼94% in the visible region.After the characterization of ITO, the OLEDs with the structure of Glass/ITO/ PEDOT:PSS/Alq3/Al were fabricated. Then the current density–voltage, resistance-voltage, power-voltage, and irradiance-voltage of the OLEDs were characterized. The results showed that decreasing EML thickness leads to a reduction of turn-on voltage, resistance, and power. The peak emission intensity of 55 nm thickness EML was stronger and sharper of others.