光子晶体增强型OLED的FDTD模拟

Organic light emitting diode devices (OLED) have potential applications in  flat panel displays, flexible displays and illumination devices. In this paper the effect of  a photonic crystal structure in the glass substrate on the emission characteristics is  investigated by means of FDTD simulations.

In this paper a photonic crystal structure (PC) based on air holes in a glass substrate is  designed. It has a TE band gap but TM waves do not have a forbidden band. By a 3D  FDTD simulation using periodic boundary condition (PBC), this structure was excited  by a dipole in the center of the structure at the interface of the hole transport layer  (HTL) and the electron transport layer (ETL). The near-field out-coupled light is  recorded for the case with and the case without photonic crystal. It is shown that for the  structure with photonic crystal the light emission in OLED is suppressed.

The geometry of the photonic crystal enhanced OLED has been illustrated in figure.3.  The structure is excited by a sinusoidal electric dipole at the HTL/ETL interface, with  frequency corresponding to a wavelength λ=530nm for 4096 time steps (equivalent to  about 32 periods). The dielectric parameters are given in Table 1.

The simulation volume is X=250×dx, Y=250×dy where dx=dy=dz=λ/32. dt=dx/4/c. The  periodic boundary condition (PBC) is used for the four sides of the volume and the  perfectly matched layer (PML) boundary condition for top and bottom . The structure is  analyzed with photonic crystal and without photonic crystal. The near-field plot of the z  component of poynting vector in the OLED without photonic crystal is shown in figure.  4a. In figure. 4b the near-field plot of the z component of poynting vector is shown for  the structure with photonic crystal.

It is obvious that in one period of oscillation more energy is confined near the location  of the dipole in the photonic crystal enhanced OLED (Figure. 5). The ratio of the  extracted energy of enhanced OLED over the simple OLED is illustrated in figure 6 as a  function of the radial distance from the dipole.

Fig5

Optical extraction of a photonic band gap enhanced OLED was simulated by 3D FDTD  method. The metallic layer is modeled as a dispersive material. It is shown that photonic  band gap enhancement confines the near-field emission and increases the contrast of the  OLED.