Numerical Simulation on Electrical and Optical Characteristics of ITO/TAD/S-DPVBi/Alq3 OLED Structure

초록

In this paper, we report our numerical study on the electronic-optical properties of the organic light emitting diodes (OLEDs) devices with n-doped layer, which is inserted for the purpose of reducing the interface barrier height between the cathode and the ETL(electron transport layer). We undertake the finite element method (FEM) for in OLEDs with n-doped layer in order to understand the transport behavior of carriers, recombination kinetics, and emission property. Our model includes Poisson’s equation, continuity equation to account for behavior of electrons and holes and the exciton continuity/transfer equation to account for recombination of carriers. We employ the multilayer structure that consists of indium tin oxide (ITO); 2, 2’, 7, 7’ –tetrakis (N, N-diphenylamine) - 9, 9’- spirobi-fluorene (spiro TAD); 4, 4’- bis (2,2’- diphenylvinyl) - 1,1’- spirobiphenyl (S-DPVBi); tris (8-quinolinolato) aluminium (Alq3); calsium (Ca). Especially, we focus on the current characteristics for thickness of n-doping layer and for the variation of doping concentration. The calculated exciton density profiles are illustrated in Figure 1(a). The simulation results imply that the recombination takes place mostly at S-DPVBi/Alq3 interface. Keeping the charge injection rates at the electrodes unchanged, we varied the internal barrier height from 0eV to 0.3eV as shown in Figure 1(b). If the internal barrier height is decreased, the accumulation on the Alq3 side of the interface will enhance the short-lived overshoot peak. The results of Figure 1(a),(b) do not contain n-doped layer. But the result of Figure 1(c) contains n-doped layer. With increasing the doping concentration, the recombination efficiency seems to imply a good response time as shown in Figure 1(c).