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<p>Cross-linkable hole transport materials (x-HTMs) play a crucial role in solving the issue of interlayer mixing of solution-processed organic light-emitting diodes (OLEDs). However, issues such as energy level mismatch and low hole mobility hinder the application of x-HTMs in deep-blue OLEDs. In particular, thermally activated delayed fluorescent (TADF) emitters require HTMs with high triplet energies (<i>E</i><sub>T</sub>) to ensure high exciton utilization efficiency. Here, two star-shaped cross-linkable HTMs 5-(9<i>H</i>-carbazol-9-yl)-<i>N</i><sup>1</sup>,<i>N</i><sup>3</sup>-di(<i>p</i>-tolyl)-<i>N</i><sup>1</sup>,<i>N</i><sup>3</sup>-bis(4-vinylphenyl)benzene-1,3-diamine (m-V-CzDPA) and <i>N</i><sup>1</sup>,<i>N</i><sup>1</sup>-diphenyl-<i>N</i><sup>3</sup>,<i>N</i><sup>5</sup>-di(<i>p</i>-tolyl)-<i>N</i><sup>3</sup>,<i>N</i><sup>5</sup>-bis(4-vinylphenyl) benzene-1,3,5-triamine (m-V-DPADPA) were designed and synthesized. Owing to their aromatic torsion structures, m-V-CzDPA and m-V-DPADPA possessed high <i>E</i><sub>T</sub>s of 2.89 and 2.87 eV, respectively, which can effectively confine triplet excitons in the emitting layer (EML). The carrier diffusion coefficients of their x-HTMs, x-m-CzDPA and x-m-DPADPA, which were obtained via carrier diffusion imaging characterization were 0.54 and 0.44 cm<sup>2</sup> s<sup>−1</sup>, respectively, thus indicating outstanding intrinsic hole transport capacity, with hole mobilities of 4.30×10<sup>−4</sup> and 1.39×10<sup>−4</sup> cm<sup>2</sup> V<sup>−1</sup> s<sup>−1</sup>, respectively. Solution-processed deep-blue TADF-OLEDs employing x-m-CzDPA as the HTM achieved a maximum current efficiency/maximum external quantum efficiency of 5.25 cd A<sup>−1</sup>/18.06%, with CIE coordinates of (0.162, 0.042). This is the first time that x-HTMs have served as efficient deep-blue TADF-OLEDs via a solution process, which also meets the latest BT. 2020 standard (CIE<sub><i>y</i></sub> ⩽ 0.046).</p>

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Star-shaped cross-linkable hole transport materials with high triplet energy and deep HOMO energy enable efficient solution-processed deep-blue TADF OLEDs

  • 期刊论文

  • 发表日期：

    2025年8月15日

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  • Jiaxu Bai,
  • Jingyuan Feng,
  • Chuanxin Liao,
  • Tianhao Wang,
  • Shirong Wang,
  • Hongli Liu,
  • Xianggao Li

摘要

Cross-linkable hole transport materials (x-HTMs) play a crucial role in solving the issue of interlayer mixing of solution-processed organic light-emitting diodes (OLEDs). However, issues such as energy level mismatch and low hole mobility hinder the application of x-HTMs in deep-blue OLEDs. In particular, thermally activated delayed fluorescent (TADF) emitters require HTMs with high triplet energies (ET) to ensure high exciton utilization efficiency. Here, two star-shaped cross-linkable HTMs 5-(9H-carbazol-9-yl)-N1,N3-di(p-tolyl)-N1,N3-bis(4-vinylphenyl)benzene-1,3-diamine (m-V-CzDPA) and N1,N1-diphenyl-N3,N5-di(p-tolyl)-N3,N5-bis(4-vinylphenyl) benzene-1,3,5-triamine (m-V-DPADPA) were designed and synthesized. Owing to their aromatic torsion structures, m-V-CzDPA and m-V-DPADPA possessed high ETs of 2.89 and 2.87 eV, respectively, which can effectively confine triplet excitons in the emitting layer (EML). The carrier diffusion coefficients of their x-HTMs, x-m-CzDPA and x-m-DPADPA, which were obtained via carrier diffusion imaging characterization were 0.54 and 0.44 cm2 s−1, respectively, thus indicating outstanding intrinsic hole transport capacity, with hole mobilities of 4.30×10−4 and 1.39×10−4 cm2 V−1 s−1, respectively. Solution-processed deep-blue TADF-OLEDs employing x-m-CzDPA as the HTM achieved a maximum current efficiency/maximum external quantum efficiency of 5.25 cd A−1/18.06%, with CIE coordinates of (0.162, 0.042). This is the first time that x-HTMs have served as efficient deep-blue TADF-OLEDs via a solution process, which also meets the latest BT. 2020 standard (CIEy ⩽ 0.046).