Song Jiayi, Guan Yunxia, Wang Cheng, Bao Xi, Li Wanjiao, Chen Lijia, Niu Lianbin
College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing, 401331, People's Republic of China.
Phys Chem Chem Phys. 2023 Sep 13;25(35):23783-23791. doi: 10.1039/d3cp02332j.
Although the effect of the electron transport layer (ETL) material TmPyPb on the electroluminescence performance of organic light-emitting diodes (OLEDs) has been extensively studied, the process of TmPyPb regulating exciton recombination and annihilation within the device is still unclear. Here, we fabricated devices of various TmPyPb thicknesses with and without ETL. Subsequently, we measured the magneto-electroluminescence (MEL) of these devices. Specifically, at the same luminance, the triplet-charge annihilation (TQA) process is more likely to occur as the thickness of TmPyPb increases, resulting in a decrease in the maximum luminance of devices. Due to electron leakage and exciton recombination region moving towards the cathode, leading to a decrease in luminance efficiency at first and then an enhancement with an increase in the thickness of TmPyPb. Furthermore, at room temperature, the application of a large bias voltage suppresses singlet fission (SF) processes by modulating the dissociation of singlet polaron pairs (PP) and the concentration of triplet exciton (T). This leads to the conversion of SF to the TQA process. At low temperatures, the bias voltage and temperature can regulate the concentration and lifetime of PP and T. Therefore, as the temperature decreases, the transition of SF → TQA → triplet-triplet annihilation (TTA) and TQA coexistence → TTA process occurs. Moreover, MEL responses of the TmPyPb-ETL device show a W-linear pattern owing to the combined effect of the hyperfine interaction (HFI) and Zeeman splitting at 145 K. Accordingly, we explored the electroluminescence (EL) performance of TmPyPB-ETL OLEDs and investigated the evolution of SF, TQA, and TTA processes using MEL. Our study revealed the effect of exciton recombination and annihilation in OLEDs with varying thicknesses of TmPyPb.
尽管电子传输层（ETL）材料TmPyPb对有机发光二极管（OLED）电致发光性能的影响已得到广泛研究，但TmPyPb调节器件内激子复合和湮灭的过程仍不清楚。在此，我们制备了有和没有ETL的不同TmPyPb厚度的器件。随后，我们测量了这些器件的磁电致发光（MEL）。具体而言，在相同亮度下，随着TmPyPb厚度增加，三重态电荷湮灭（TQA）过程更易发生，导致器件的最大亮度降低。由于电子泄漏和激子复合区域向阴极移动，起初导致发光效率降低，随后随着TmPyPb厚度增加而增强。此外，在室温下，施加较大偏置电压通过调制单重极化子对（PP）的解离和三重态激子（T）的浓度来抑制单重态裂变（SF）过程。这导致SF向TQA过程的转变。在低温下，偏置电压和温度可调节PP和T的浓度及寿命。因此，随着温度降低，发生SF→TQA→三重态-三重态湮灭（TTA）以及TQA共存→TTA过程的转变。此外，由于在145 K时超精细相互作用（HFI）和塞曼分裂的综合作用，TmPyPb-ETL器件的MEL响应呈现W线性模式。据此，我们探索了TmPyPB-ETL OLED的电致发光（EL）性能，并使用MEL研究了SF、TQA和TTA过程的演变。我们的研究揭示了不同厚度TmPyPb的OLED中激子复合和湮灭的影响。
