迁移率对单层有机发光器件中电场与载流子分布的影响

有机发光器件的宏观特性与有机层中的电场和载流子浓度分布密切相关。建立的有机电致发光器件模型是由两个金属电极中间夹一层有机发光薄膜材料组成的单层器件,金属与有机发光层之间为欧姆接触。模型以载流子运动的扩散-漂移理论为基础,利用数值方法研究了有机发光层中双极载流子注入时的电势、电场、载流子浓度和复合密度分布。分析结果表明:当两种载流子的迁移率相同时,电场强度、载流子浓度、复合密度的分布呈对称形式。而当电子和空穴的迁移率μn和μp相差比较大时,高迁移率的载流子不仅仅分布在注入端附近而且还有一小部分能够传输到另一端,而低迁移率的载流子只分布在其注入端附近;当μn、μp的大小相差不大时,载流子传输情况就介于两者之间。当μn/μp的比值变化时,电场强度的极大值向载流子迁移率小的注入端偏移。

Effect of Mobility on the Distribution of Electric Field and Carrier Density in Single Layer Organic Light Emitting Devices

The performance of organic light emitting devices(OLEDs)is closely related to the electric field intensity and carrier density distribution in the organic layer.Based on the drift-diffusion theory for the motion of charge carriers,we considered the OLED structure consists of a single layer of luminescent organic material sandwiched between two metallic electrodes,the contacts between the metallic electrodes and organic material are ohmic.We adopted the method of numerical calculation to study the potential,electric field intensity,carrier density and recombination rate in the organic material.The results shown these:(1)when holes and electrons have the same mobility,the distribution of the potential,electric field,carrier density and recombination rate is symmetrical.This is because the influence of two different carriers' injection is the same.Most carriers distribute near the electrodes and decrease very fast,the interface of metal/semiconductor contact is just like a carrier packet and the carrier density is very low in the middle of the device,so the electric fields near the two contacts are much stronger than that in the middle.(2)When the mobility of holes and electrons differs greatly,the higher mobility carriers can not only distribute near the injecting electrode but also transmit to another electrode.However,the lower mobility carriers distri-bute mainly near the injecting electrode.When the mobility difference of electron and hole is small,the distribution of the carriers is between the above two cases.When the ratio of hole mobility to electron mobility changes,the position of the maximum of the electric field moves to the electrode from which the low mobility car-riers are injected.