Numerical simulation on white OLEDs with dotted-line doped emitting layers

摘要

White organic light-emitting diodes (OLEDs) have attracted great attention recently. In this study, high-efficiency white organic light-emitting diodes with dotted-line doped layers are numerically investigated with the APSYS (abbreviation of Advanced Physical Model of Simulation Devices) simulation program. The APSYS simulation program, developed by Crosslight Inc., is capable of dealing with the optical, electrical, and thermal characteristics of OLED devices. To approach the real situation, the OLED device fabricated by Park et al. (Current Applied Physics 1, 116, 2001) was first modeled by adjusting the appropriate physical parameters. Based on this OLED structure, a new structure of ITO/a-NPD (40 nm)/Alq_3:DCJTB (30 nm)/Alq_3 (30 nm)/Mg:Ag emitting quasi-white light was then proposed. Then, the single layer of Alq_3:DCJTB was replaced by multi-(Alq_3:DCJTB/Alq_3)n layers, which are the so-called dotted-line doped layers (see, e.g., paper by Han et al., Solid State Communications 141, 332, 2007), to further improve the optical performance. The optical properties of the white OLEDs with different pairs of (Alq_3:DCJTB/Alq_3)n dotted-line doped layers are investigated and discussed in detail. Optimization of the proposed quasi-white OLED structures is attempted. The simulation results indicate that the OLED with dotted-line doped layers has higher radiative recombination rate and better emission efficiency than that with a single Alq_3:DCJTB layer. The physical origin of the improved optical performance for the OLED with dotted-line doped layers could be due to the increased electrons and holes at the interfaces between the Alq_3:DCJTB and Alq_3 layers, which thus results in higher radiative recombination rate and better emission efficiency.