Dimers or Solid‐State Solvation? Intermolecular Effects of Multiple Donor–Acceptor Thermally Activated Delayed Fluorescence Emitter Determining Organic Light‐Emitting Diode Performance
Dimers or Solid‐State Solvation? Intermolecular Effects of Multiple Donor–Acceptor Thermally Activated Delayed Fluorescence Emitter Determining Organic Light‐Emitting Diode Performance
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DOI：
10.1002/adom.202002153
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发表时间：
2021-03
影响因子：
9
通讯作者：
P. Imbrasas;R. Lygaitis;P. Kleine;R. Scholz;Christian Hänisch;S. Buchholtz;K. Ortstein;F. Talnack;S. Mannsfeld;Simone Lenk;S. Reineke
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作者：
P. Imbrasas;R. Lygaitis;P. Kleine;R. Scholz;Christian Hänisch;S. Buchholtz;K. Ortstein;F. Talnack;S. Mannsfeld;Simone Lenk;S. Reineke
具有热激活延迟荧光（TADF）的有机发光材料在改善显示应用方面显示出巨大的前景。最近，发光分子之间的分子间效应受到了更多的关注，揭示了强烈的固态溶剂化或聚集诱导的样品性能变化。这对器械性能的影响尚未完全涵盖。在这项工作中，提供了一种新的TADF发射体，2，3，4，5，6-五（咔唑-9-基）苯甲酸甲酯（5CzCO 2 Me）的彻底研究。稳态发射光谱揭示了随着小分子主体中发射体浓度的增加，发光红移。在所有研究的浓度下，发射曲线保持不变;因此，红移归因于固态溶剂化效应。在20wt%的样品中实现了最高的光致发光量子产率（PLQY），达到66%。在电流-电压-亮度和外量子效率（EQE）参数方面最好的有机发光二极管（OLED）是具有60重量%发射体浓度的器件，达到7.5%的最大EQE值。结果表明，发射极传输空穴，并且电荷载流子复合不会发生在主体的带隙上，而是看到混合的主体-客体浓度依赖性复合。5CzCO 2 Me的空穴传输特性允许通过控制发射极浓度来调整器件性能的新维度。
Organic light‐emitting materials exhibiting thermally activated delayed fluorescence (TADF) show great promise for improving display applications. Recently, intermolecular effects between emitting molecules have been given more attention, revealing strong solid‐state solvation or aggregation induced changes of sample performance. Implications of this on device performance are not yet fully covered. In this work, a thorough investigation of a novel TADF emitter, methyl 2,3,4,5,6‐penta(carbazol‐9‐yl)benzoate (5CzCO2Me), is provided. Steady‐state emission spectra reveal a luminescence redshift with increasing emitter concentration in a small molecule host. In all investigated concentrations, the emission profile remains the same; thus, the redshift is attributed to the solid‐state solvation effect. The highest photoluminescence quantum yield (PLQY) is achieved in the 20 wt% sample, reaching 66%. The best organic light‐emitting diode (OLED) in terms of current–voltage–luminance and external quantum efficiency (EQE) parameters is the device with 60 wt% emitter concentration, reaching maximal EQE values of 7.5%. It is shown that the emitter transports holes and that charge‐carrier recombination does not take place on the bandgap of the host, but rather, a mixed host–guest concentration‐dependent recombination is seen. The hole‐transporting properties of 5CzCO2Me allow for a new dimension in tuning the device performance by controlling the emitter concentration.