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热活化延迟荧光(TADF)器件中,三线态激子可以吸收环境热量通过反向系间窜越(RISC)转化为单线态激子从而发出延迟荧光,可望实现100%的内量子效率.为揭示TADF器件中电致发光的微观机制,本文选取4CzTPN-Ph,2CzPN,PIC-TRZ2三种不同带隙的高效TADF材料制成有机发光器件,测量并分析器件的电致发光磁效应(MEL).研究发现,尽管这几种TADF器件具有增强发光的RISC过程,但它们的MEL曲线却表现出与不具有RISC过程的普通荧光器件相似的线型,这是由于外加磁场只影响极化子对间的超精细相互作用,而并不影响激子间的系间窜越与RISC过程.但是,这些TADF器件的磁效应幅度却会随注入电流的增加而变强,表现出与普通荧光器件相反的结果,电流对三线态激子的形成速率kt和单线态激子的形成速率ks的相对影响(kt/ks)被用来解释了这一反常结果.
In TADF devices, triplet excitons can absorb 100% of the ambient heat and transform into singlet excitons via reverse intersystem crossing (RISC) to emit delayed fluorescence, which is expected to achieve 100% internal quantum efficiency. In order to reveal the microscopic mechanism of electroluminescence in TADF device, three efficient TADF materials with different bandgaps, such as 4CzTPN-Ph, 2CzPN and PIC-TRZ2, were selected as the organic light-emitting devices to measure and analyze the electroluminescent magnetic effect (MEL) The study found that although these TADF devices have RISC processes that enhance luminescence, their MEL curves exhibit similar linear patterns as conventional fluororesins without the RISC process because the applied magnetic field only affects polaron pairs But does not affect the intersystem crossing and the RISC process between excitons.However, the magnetic effect amplitude of these TADF devices becomes stronger with the increase of the injection current, which shows the opposite of the ordinary fluorescent device , The relative effect (kt / ks) of the current on the rate of formation of triplet excitons kt and singlet exciton formation rate ks (kt / ks) is used to explain this anomalous result.