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首页> 外文学位 >Electronic Properties and Charge Transport of Polyhedral Oligomeric Silsesquioxanes (POSS) Derivatives and Materials Design for Highly Efficient Organic Light Emitting Diodes.
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Electronic Properties and Charge Transport of Polyhedral Oligomeric Silsesquioxanes (POSS) Derivatives and Materials Design for Highly Efficient Organic Light Emitting Diodes.

机译：多面体低聚倍半硅氧烷（POSS）衍生物的电子性能和电荷传输以及高效有机发光二极管的材料设计。

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摘要

Polyhedral oligomeric silsesquioxane (POSS) and its derivatives are used as examples to illustrate the tunability of electronic properties of organic semiconductors by density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies. The results indicate that the POSS cage is quite rigid upon functionalization and thus provides a means for controlling the orientation of organic fragments attached to it. Moreover, the electronic properties such as frontier orbitals distribution and energy level, HOMO-LUMO gap, reorganization energy, and exciton binding energy can be tuned through the choice of functional groups and their positioning. By functionalizing the POSS cage with two pentacene molecules along the diagonal direction, we construct Dipentacene POSS with very high charge mobility predicted by multiscale modeling. Unlike the herringbone pattern in the pentacene single crystal, the Dipentacene POSS molecules adopt a parallel configuration in its single crystal that was predicted with molecular dynamics. This parallel configuration enhances the wavefunction overlap between pentacene segments, resulting in faster charge hopping between the molecules. The insight gained in the tuning of electronic properties and charge transport was used to design materials for organic light emitting diodes (OLEDs). We optimized the molecular structures of emitting materials based on first-principles calculations, resulting in a remarkable improvement in the maximum external quantum efficiency (EQE) of the undoped device from 2.0% to 4.99%. By doping the emitters in suitable host material, 4,4'-bis(carbazol-9-yl)biphenyl (CBP), at the optimal doping concentration, deep blue emission with extremely high maximum EQE of 10.7% and CIE coordinates of (0.151, 0.088) were achieved. The high EQE far exceeds the traditional upper limit of 5% if the singlet generation fraction in fluorescent OLEDs is 25%. A survey of the literature published in the last two decades indicates that singlet generation fraction can be higher than 25%. Using a model developed from Fermi's golden rule, we found that singlet generation fraction of most of the organic emitters for OLEDs is in the range of 40%--70%. The successful materials design for OLEDs suggests that we can prescreen and optimize molecular structures before synthesis in the lab, to avoid iterative and costly Edisonian approaches.
机译：以多面体低聚倍半硅氧烷（POSS）及其衍生物为例，通过密度泛函理论（DFT）和时变密度泛函理论（TDDFT）研究来说明有机半导体电子特性的可调性。结果表明，POSS笼在功能化时非常坚固，因此提供了一种控制附着在其上的有机片段取向的手段。此外，可以通过选择官能团及其位置来调整电子特性，例如边界轨道分布和能级，HOMO-LUMO间隙，重组能和激子结合能。通过使用沿对角线方向的两个并五苯分子功能化POSS笼，我们构建了通过多尺度建模预测的具有非常高电荷迁移率的双并五烯POSS。与并五苯单晶中的人字形图案不同，双并五烯POSS分子在其单晶中采用平行构型，这是通过分子动力学预测的。这种平行构型增强了并五苯链段之间的波函数重叠，从而导致分子之间的电荷跳变更快。在调节电子性能和电荷传输中获得的见识被用于设计有机发光二极管（OLED）的材料。我们基于第一性原理计算优化了发光材料的分子结构，从而使未掺杂器件的最大外部量子效率（EQE）从2.0％显着提高到4.99％。通过以合适的掺杂浓度将发射体掺杂到合适的基质材料4,4'-双（咔唑-9-基）联苯（CBP）中，深蓝色发射具有极高的最大EQE为10.7％和CIE坐标为（0.151） （0.088）。如果荧光OLED中的单重态生成比例为25％，则高EQE远远超过了5％的传统上限。最近二十年来发表的文献调查表明，单重态生成比例可能高于25％。使用费米黄金法则开发的模型，我们发现大多数OLED有机发光体的单重态生成比例在40％-70％的范围内。 OLED的成功材料设计表明，我们可以在实验室合成之前进行预筛选和优化分子结构，以避免迭代和昂贵的爱迪生方法。

著录项

  • 作者

    Zhen, Changgua.;

  • 作者单位

    University of Michigan.;

  • 授予单位 University of Michigan.;
  • 学科 Chemistry Molecular.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 194 p.
  • 总页数 194
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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