SCIENTIA SINICA Informationis, Volume 50 , Issue 1 : 151-162(2020) https://doi.org/10.1360/N112019-00027

Study of the microscopic mechanism of Ir(ppy)$_{3}$ regulating exciton splitting and luminescence process in Rubrene

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  • ReceivedJan 29, 2019
  • AcceptedMay 5, 2019
  • PublishedJan 9, 2020


To explore the microscopic mechanism of singlet exciton splitting (${\rm~S}_{1}+{\rm~S}_{0}\to~{\rm~T}_{1}+~{\rm~T}_{1}$, STT) and luminescence in Rubrene, a phosphorescent material Ir(ppy)$_{3}$ with strong spin-orbit coupling (SOC) and green emission was selected and mixed into Rubrene thin films with different proportions to fabricate a series of luminescent devices. By measuring the magneto-electroluminescence (MEL) and current-luminescence ($I$-$B$) curves of the devices under different temperatures and currents, we found that the MEL profiles of light-emitting devices with different mixing ratios at room temperature show an STT fingerprint characteristic curve of magnetic field modulation. MEL amplitude first increases and then decreases with increased mixing ratio, whereas luminescence intensity increases monotonously. This is different from conventional Rubrene doped devices (such as mCP: $y$%Rubrene) which show STT increases with increasing concentration but with decreasing luminescence . By analyzing the singlet and triplet energy levels and emission spectra of Ir(ppy)$_{3}$ and absorption spectra of Rubrene, it can be seen that aside from Rubrene's molecular space's influence on the STT process, intersystem crossing (ISC) caused by the strong SOC of Ir(ppy)$_{3}$ and energy transfer processes between the T$_{1}$ exciton of Ir(ppy)$_{3}$ and the S$_{1}$ exciton of Rubrene are also included in the devices. The combined action of these three micro-mechanisms leads complex MEL and luminescence changes in the device, and the device's current density and working temperature also have a good regulatory effect on them. Obviously, this study helps with understanding of the microscopic process and its evolution mechanism based on Rubrene optoelectronic devices.

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  • Figure 1

    (Color online) The device optical and electronic properties. (a) The diagram of device structure; (b) the $I$-$V$ curves of devices, the inset is the molecular structures; (c) the normalized PL spectra of Ir(ppy)$_3$ and Rubrene films;protect łinebreak (d) the brightness intensity of devices with different concentrations under various injection currents at room temperature

  • Figure 2

    (Color online)The MEL response curves of the reference device and the Rubrene: 10%Ir(ppy)$_3$device at different temperatures and injection currents. (a)–(d) Rubrene: 10%Ir(ppy)$_3$ devices; (e)–(h) reference devices

  • Figure 3

    (Color online) (a) Temperature-dependent MEL curves of the Rubrene:10%Ir(ppy)$_{3}$ device at 10 $\mu~$A;protect łinebreak (b) temperature-dependentMEL$_{\rm~HFE}$ values of the reference device and the Rubrene:10%Ir(ppy)$_{3}$ device

  • Figure 4

    (Color online) (a) Mixing concentrations-dependent MEL curves ofdevice Rubrene: $x$%Ir(ppy)$_{3}$ at room temperature when the current is 10$\mu~$A; (b) mixing concentrations-dependent MEL$_{\rm~HFE}$ value underdifferent currents at room temperature; (c) mixing concentrations-dependentMEL curves of device Rubrene: $x$%Ir(ppy)$_{3}$ at 20 K when the current is10 $\mu~$A; (d) mixing concentrations-dependent MEL$_{\rm~HFE}$ value underdifferent temperature at 10 $\mu~$A

  • Figure 5

    (Color online) (a) The microscopic processes of devices; (b) theschematic of microscopic process of exciton and polaron betweenIr(ppy)$_{3}$ and Rubrene at low concentration mixing; (c) the MEL$_{B~=~300}$ values and brightness intensity of devices with various differentconcentrations at room temperature and the injection current of 10 $\mu~$A;(d) the schematic of microscopic process of exciton and polaron betweenIr(ppy)$_{3}$ and Rubrene at high concentration mixing. The circlesrepresent Rubrene, and the triangles represent Ir(ppy)$_{3~}$ in (b) and (d)

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