利用发光磁效应分析高温环境对OLED中激子演化的影响

Using magneto-electroluminescence to analyze the influence of high temperature environment on exciton evolution processes in organic light-emitting diodes

本文制备了基于红荧烯(Rubrene)材料的有机发光二极管(OLED),并利用磁电致发光效应(MEL)分析了高温环境对器件中激子演化的影响.器件的MEL在高、低外加磁场范围内的线型特征表明,室温下激子的演化以单重态激子分裂(STT)过程为主,而在420 K环境温度下,器件的STT过程减弱,但出现了系间窜越(ISC)这一激子演化过程.结合器件的表面形貌、发光-电流特性、电流效率和光谱,我们认为高温环境导致Rubrene薄膜中产生了大量的结构缺陷,限制了器件内部极化子对和激子的扩散,提高了单重态和三重态极化子对间的转换效率,从而导致高温环境下出现不利于内量子效率的ISC过程.但缺陷对激子的俘获作用会抑制单重态激子向三重态激子的转换,导致STT过程在高温环境下减弱,从而提升器件的内量子效率.本研究不仅有利于理解高温环境对Rubrene型OLED器件中激子演化过程的影响,还提供了一种利用有机发光磁效应无损探测器件发光层结构改变的技术方案.

An organic light-emitting diode(OLED)based on rubrene was fabricated,and the magneto-electroluminescence(MEL)was used to analyze the exciton evolutions in the device under high temperature environment.The MEL characteristics of the device in the high and low applied magnetic fields indicate that the exciton evolution at room temperature is dominated by singlet exciton splitting(STT)processes,420 K ambient temperature the STT process weakens,but the exciton evolution process of intersystem crossing(ISC)occurs.Combined with the surface morphology,luminescencecurrent characteristics,current efficiency and spectrum of the device,we believe that the high temperature environment causes a large number of structure defect in the rubrene film.The defect limits the diffusion of the polaron pairs and excitons inside the device,and improves the conversion efficiency between the singlet polaron pairs and triplet polaron pairs,and results in an ISC process that is not conducive to internal quantum efficiency in high temperature.The capture of excitons inhibits the conversion of singlet excitons to triplet excitons,resulting in a weakening of the STT process in high temperature environments,thereby increasing the quantum efficiency of the device.It not only deepens the understanding of the influence of high temperature environment on the exciton evolution process in rubrene type OLED devices,but also provides a technical solution to monitor the structural changes of devices by using organic luminescence magnetic effect.