Effect of Thickness of Tris (8-Hydroxyquinolinato) Aluminum on the Photoluminescence and I-V Characteristic of Organic Light Emitting Structure

Problem statement: How the thickness of the tris (8-hydroxyquinolinato) Aluminum (Alq₃) effect the optical and electrical properties of organic light emitting diode. Approach: The optimum thickness, photoluminescence and current-voltage characteristic of Alq₃ layer on N, N-bis (inaphthyl)- N,N-diphenyl-1,1-biphenyl-4,4-diamine (55 nm) layer in Organic Light-Emitting Devices (OLED) structure are reported. Alq₃ and NPB organic layers are used as Electron Transport Layer (ETL) and as Hole Transport Layer (HTL) in Organic Light-Emitting Devices (OLED). The thin layers of the NPB and Alq₃ were prepared by thermal evaporation method. Results: The Alq₃ layer was evaporated on the NPB layer for thickness ranging from 16 to 134 nm and photoluminescence and I-V characteristic were studied using fiber optics spectrophotometer (Ocean Optics- USB 2000 FLG) and current-voltage source (Keithley, model 2400). Conclusion: It was found that the Alq₃ with 84 nm thicknesses gives the highest photoluminescence peak at 520 nm wavelengths, as well as the lowest turn on voltage of the device. The optical reflectance spectra for every sample were also reported.