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1、 V.S. Sunderam et al. (Eds.): ICCS 2005, LNCS 3516, pp. 300 308, 2005. Springer-Verlag Berlin Heidelberg 2005 Adaptive Finite Volume Simulation of Electrical Characteristics of Organic Light Emitting Diodes Yiming Li1,2 and Pu Chen2 1 Department of Computational Nanoelectronics, National Nano Device
2、 Laboratories, Hsinchu 300, Taiwan 2 Microelectronics and Information Systems Research Center, National Chiao Tung University, Hsinchu 300, Taiwan ymlifaculty.nctu.edu.tw Abstract. In this paper a two-dimensional simulation of organic light emitting devices (OLEDs) using an adaptive computing techni
3、que is presented. A set of drift-diffusion equations including models of interface traps is solved numeri-cally to explore the transport property of OLED structures. The adaptive simu-lation technique is mainly based on the Gummels decoupling algorithm, a finite volume approximation, a monotone iter
4、ative method, a posteriori error estima-tion, and an unstructured meshing scheme. With this computational approach, we investigate the intrinsic and terminal voltage-current characteristics of OLEDs with respect to different material parameters, thickness of materials, and length of structure. 1 Int
5、roduction Organic electroluminescence has been of great interest in various display applications. Organic light emitting diode (OLED) displays are lightweight, durable, power effi-cient and ideal for portable applications 1. They have lower material costs and fewer processing steps than their liquid
6、 crystal display (LCD) counterparts. As such, the OLED display appears to be a strong candidate as a replacement technology in a vari-ety of mobile application areas. OLEDs with different thin-film structures, consisting of emitter and carrier transport layers, have recently been reported 2, 3, 4, 5
7、, 6. According to the simple device geometry in OLEDs, one-dimensional (1D) trans-port model, the drift-diffusion model, has generally been solved along the transport direction for studying the electrical properties of OLEDs 4, 5, 6. However, a multidimensional modeling and simulation plays a crucia
8、l role for exploring the effect of device structure and material on the electrical characteristics of OLEDs. In this paper a set of drift-diffusion (DD) equations is solved with an adaptive computing technique 7, 8, 9, 10 for a two-dimensional (2D) simulation of OLEDs. For the simulation of OLEDs, t
9、he DD equations consist of the Poisson equa-tion, the current continuity equation of electron, the current continuity equation of hole, and models of interface traps. First of all we decouple the three partial differen-tial equations (PDEs) according to the Gummels procedure. Based on adaptive un-st
10、ructured mesh and finite volume (FV) approximation, each decoupled PDE is dis-cretized and then solved by means of the monotone iterative (MI) method instead of Adaptive Finite Volume Simulation of Electrical Characteristics of OLEDs 301 Newtons iteration (NI) method. The method of monotone iteratio
11、n is a constructive alternative for numerical solutions of PDEs. It has been reported that, compared with the NI method, the major features of the MI method are (1) it converges globally with any arbitrary initial guesses; (2) its implementation is much easier than NI method; and (3) it is inherentl
12、y ready for parallelization 8. Furthermore, due to the efficient posteriori error estimation, the variation of physical quantities, such as the gradients of potential and current density, can be automatically tracked. Therefore, the terminal characteristics are accurately calculated. The proposed ad
13、aptive computing technique shows the simulation accuracy and numerical robustness for the simulation of 2D OLEDs. Effects of geometry, the trap density and the Schottky barrier height 11 on the current-voltage (I-V) curves of the simulated 2D OLED are examined using the developed 2D simulation progr
14、am. This paper is organized as follows. In the section 2, we state the transport model and the adaptive computing technique for the 2D simulation of OLED. In the section 3, the results of numerical simulation are discussed. Finally we draw the conclusions. Fig. 1. A cross-sectional view of the studi
15、ed OLED structure, where LA is the length of contacts of anode and Lx is the length of contact of cathode. The Ly1 is the width of material Alq3 which is the layer of electron transport and the Ly2 is the width of material TPD which is the layer of hole transport 2 Mathematical Model and Computation
16、al Methodology Based on the well-known inorganic charge transport continuum model 9, the drift-diffusion model, electron and hole transport in the OLED is described using the cur-rent continuity equations coupled to the Poisson equation 11. Along with the appro-priate boundary conditions, which for OLEDs require appropriate formalisms for current injection at each of the contacts, these equations are solved to obtain solutions for the electrostatic potential, electric field, carrier densities, a
