光子晶体结构增强有机发光二极管出光效率的理论计算

Theoretical calculation of enhancing the extraction efficiency of organic light-emitting diodes by photonic crystals

有机发光二极管(OLED)中产生的光在进入空气的过程中,会因材料折射率的不匹配而产生全内反射现象,极大地限制了器件的出光效率,最终只有20%的光能够进入空气中。采用有限时域差分(FDTD)的理论计算方法,在OLED器件中嵌入由高折射率与低折射率材料组成的光子晶体结构,研究了不同光子晶体周期、深度以及折射率参数对器件出光效率的影响。结果表明:在可见光范围内(400~700 nm),光子晶体的深度为0.45μm、周期为1.4μm、占空比为50%以及介质1与介质2折射率为2.2∶1.0时,光子晶体OLED器件的平均出光效率提高到40.7%,平均增强系数为122%。

The light extraction efficiency of organic light emitting diodes(OLED)is greatly limited due to total internal reflection,which is caused by different refractive indexes of materials.It is well-known that only 20%of the light can be out-coupling from a conventional OLED.In order to solve the key problem of low light extraction efficiency,the optical performance of OLED by finite difference time domain(FDTD)was investigated theoretically.Based on the FDTD optical solver,a conventional OLED optical model was built and one-dimensional photonic crystal(PC)with high and low refractive indices was inserted.The effects of different photonic crystal period,depth and refractive index on the light extraction efficiency of the device were considered.Results showed that when the depth of the PC was 0.45μm,the period was1.4μm,the duty ratio was 50%,the refractive index of the dielectric 1 was 2.2 and the dielectric 2 was 1.0,the average extraction efficiency of the device in the visible light band was up to 40.7%,and the enhancement factor was 122%.