Research ArticleMATERIALS SCIENCE

Acceptor plane expansion enhances horizontal orientation of thermally activated delayed fluorescence emitters

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Science Advances  09 Oct 2020:
Vol. 6, no. 41, eaba7855
DOI: 10.1126/sciadv.aba7855
  • Fig. 1 Chemical structures and theoretical calculations of PXZPM, PXZPyPM, and PXZTAZPM.

    (A) Compounds studied in this work. (B) Calculated S1 and (C) T1 hole (green)–electron (light gray) distributions, energy levels, oscillator strengths (f), and Sr indexes with the optimized structures of excited states of PXZPM, PXZPyPM, and PXZTAZPM. CT, charge transfer; LE, locally excited. (D) The direction of the calculated TDM (as indicated by arrow) relative to the coordinate of the molecular structure. (E) The area of the corresponding acceptor moiety (x-y plane).

  • Fig. 2 Atomistic molecular dynamics simulations and p-polarized measurements for PXZPM, PXZPyPM, and PXZTAZPM.

    (A) Snapshots of the final deposition for PXZPM, PXZPyPM, and PXZTAZPM molecules doped into mCPCN host molecules on the mCPCN (100) substrate surfaces. (B) The probability per 10° distribution of TDMs for PXZPM, PXZPyPM, and PXZTAZPM by atomistic molecular dynamics simulations. (C) Measured (symbols) p-polarized photoluminescence intensity (at photoluminescence peak wavelength) of different emitting layers as a function of the emission angle and simulated curves (lines and dashed lines) with different horizontal dipole ratios (Θ//s) of PXZPM, PXZPyPM, and PXZTAZPM doped into the mCPCN host (6.0 wt %). a.u., arbitrary units.

  • Fig. 3 Photoluminescence properties of PXZPM, PXZPyPM, and PXZTAZPM.

    (A) Normalized Ultraviolet-visible absorption and fluorescence spectra of PXZPyPM and PXZTAZPM in toluene (10−5 M) at 300 K and normalized phosphorescence (77 K) spectra of PXZPyPM and PXZTAZPM in 2Me-THF (10−5 M) (excitation wavelength, 365 nm). Abs, absorption; FL, fluorescence; Ph, phosphorescence. (B) Transient photoluminescence decay curves of PXZPyPM and PXZTAZPM in toluene (10−5 M) under aerated and degassed conditions, following excitation at 377 nm, detected at 530 and 534 nm (photoluminescence peak wavelength), respectively. The instrument response function (IRF) was also shown. (C) Normalized fluorescence (300 K), fluorescence (77 K), and phosphorescence (77 K) spectra of 6.0 wt % PXZPM, PXZPyPM, and PXZTAZPM doped into the mCPCN host (excitation wavelength, 365 nm). (D) Transient photoluminescence decay curves of 6.0 wt % PXZPM, PXZPyPM, and PXZTAZPM doped into the mCPCN host at 300 K, following excitation at 377 nm, detected at 521, 524, and 528 nm (photoluminescence peak wavelength), respectively. The IRF was also shown.

  • Fig. 4 Device performance of OLEDs.

    (A) Energy level diagrams and (B) chemical structures of the materials used for devices A to C. (C) Current density–voltage-luminance curves of devices A to C. (D) Electroluminescence spectra of devices A to C at 6 V. (E) PE, current efficiency (CE), and EQE versus luminance curves of devices A to C. (F) The comparison of theoretical EQEs and experimental EQEs.

  • Table 1 Photophysical properties of PXZPM, PXZPyPM, and PXZTAZPM.

    CompoundPLmax* (nm)S1† (eV)S1, 77K† (eV)T1† (eV)ΔEST‡ (eV)τp§ (ns)τd§ (μs)ФPL|| (%)Фpd¶ (%)kr# (107 s−1)kISC# (107 s−1)kRISC# (105 s−1)
    PXZPM5212.622.582.540.0420.22.5610065/353.221.736.02
    PXZPyPM5242.602.602.530.0719.42.7710065/353.351.805.57
    PXZTAZPM5282.562.582.530.0520.42.799361/322.991.695.45

    *Measured in the mCPCN host (6.0 wt %) at 300 K.

    †Calculated from the onset wavelengths of fluorescence (300 K), fluorescence (77 K), and phosphorescence (77 K) spectra of three emitters in the mCPCN host.

    ‡Calculated from the onset wavelengths of fluorescence (77 K) and phosphorescence (77 K) spectra of three emitters in the mCPCN host.

    §Measured in the mCPCN host (6.0 wt %) at 300 K.

    ||Measured in the mCPCN host (6.0 wt %) under degassed condition at 300 K. The error for ΦPL is ±1%.

    ¶The prompt and delayed fluorescence photoluminescence quantum efficiency under degassed condition at 300 K.

    #The radiative rate constant, rate constants of ISC, and RISC process of 6.0 wt % PXZPM, PXZPyPM, and PXZTAZPM doped into the mCPCN host at 300 K.

    • Table 2 Electroluminescence characteristics of the devices.

      DeviceEmitterVon* (V)Maximum
      efficiency†
      Efficiency at
      1000 cd m−2
      ηout§ (%)ηout × ΦPL|| (%)λEL¶ (nm)CIE¶ (x, y)
      CE (cd A−1), PE
      (lm W−1), and
      EQE (%)
      CE (cd A−1), PE
      (lm W−1), and
      EQE (%)
      APXZPM3.098.4, 103.5, 29.568.5, 38.9, 20.534.034.0528(0.33, 0.58)
      BPXZPyPM3.0113.5, 118.9, 33.978.6, 44.6, 23.539.139.1528(0.33, 0.58)
      CPXZTAZPM3.0101.3, 106.1, 30.162.6, 29.5, 18.639.736.9528(0.33, 0.58)

      *Turn-on voltage at 1 cd m−2.

      †Maximum efficiencies of CE (cd A−1), PE (lm W−1), and EQE (%). The error for EQE is ±0.4%, which is obtained from five devices.

      ‡Electroluminescence efficiencies recorded at 1000 cd m−2.

      §Calculated optical out-coupling efficiency.

      ||Theoretical external quantum efficiencies.

      ¶Electroluminescence peaks and CIE 1931 coordinates recorded at 6 V.

      Supplementary Materials

      • Supplementary Materials

        Acceptor plane expansion enhances horizontal orientation of thermally activated delayed fluorescence emitters

        Yepeng Xiang, Pan Li, Shaolong Gong, Yu-Hsin Huang, Chun-Yu Wang, Cheng Zhong, Weixuan Zeng, Zhanxiang Chen, Wei-Kai Lee, Xiaojun Yin, Chung-Chih Wu , Chuluo Yang

        Download Supplement

        This PDF file includes:

        • General Information
        • Photophysical Characterization
        • The Fitting of Transient Photoluminescence Decay Curves and Analyses of Rate Constants
        • X-Ray Structural Analysis of PXZPyPM
        • Determination of the Emitting Dipole Orientation of an Emitting Layer
        • Calculation of Thin-Film Emission Characteristics, OLED Optical Out-Coupling Efficiency and Theoretical External Quantum Efficiency
        • Synthesis and Characterization of PXZPyPM and PXZTAZPM
        • Figs. S1 to S10
        • Tables S1 to S4

        Files in this Data Supplement:

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