Numerical Simulation on the Charge Transport in Alq3-based OLED Structure

초록

In this paper, we report on our theoretical study on the charge transport of the multi-layer structure for organic light emitting diodes (OLEDs). Our simulation model includes Poisson’s equation, charge current equation, continuity equation, exciton continuity/diffusion/transfer equation, and light-emission and light-coupling equations. The mobility model comprises the Poole-Frenkel model for organic semiconductors. Our simulation structure comprises a hole transport layer (HTL), an emission layer (EML), and an electron transport layer (ETL) between both electrodes wherein the HTL is TPD (N, N'-Bis (3- methylphenyl) - N, N'- bis (phenyl) benzidine), and the ETL includes Alq3 (Tris (8- hyroxyquinolinato) aluminium). We investigated the carrier transport mechanism of the Alq3-based two-layer structure and thereby devised a high-efficiency device structure. We also investigated a transient response during the turn on/off period and the carrier transport in accordance with the variation of the injection barrier and applied voltage. This paper also reports the effect of the insertion of the EML and also the efficiency due to the difference in the internal barrier height. Figure 1 is a schematic energy band diagram for simulation structures which are employed in this study. Device A is a basic two-layer structure (ETL and HTL), while Device B and Device C is a three-layer structure with EML inserted. In Device B, the LUMO level of the EML aligns with the LUMO of the ETL while the HOMO level of the EML aligns with the HOMO of the HTL. In Device C, the LUMO level of the EML aligns with the LUMO of the HTL while the HOMO level of the EML aligns with the HOMO of the ETL.