3.2. OLED Fabrication and Measurement

The OLED was fabricated by vacuum thermal evaporation under pressure lower than 5 × 10⁻⁴ Pa. A 150 nm-thick indium-tin-oxide (ITO) precoated glass substrate was used as the anode. Prior to the deposition of the organic layers and cathode, the substrate was firstly cleaned with ultra-purified water, acetone, and isopropyl alcohol (IPA) in sequence, then treated with UV-ozone for 15 min and finally transferred to a vacuum thermal deposition system. The intersection of ITO and the metal electrodes gave an active device area of 4 mm². The OLED device was characterized under atmospheric conditions without any encapsulation or light out-coupling enhancement. The EL spetrum, EQE, and current density–voltage–luminance (J–V–L) characteristics of the OLED were recorded with a semiconductor parameter analyzer (E5270, Agilent, Santa Clara, CA, USA) and an optical power meter (1930C, Newport, Irvine, CA, USA). EL spectra were recorded using a multi-channel spectrometer (SD2000, Ocean Optics, Dunedin, FL, USA).