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首页> 外文期刊>ACS applied materials & interfaces >Enhancing the Performance of CdSe/CdS Dot-in-Rod Light-Emitting Diodes via Surface Ligand Modification
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Enhancing the Performance of CdSe/CdS Dot-in-Rod Light-Emitting Diodes via Surface Ligand Modification

机译：通过表面配体改性增强CDSE / CDS点棒状发光二极管的性能

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摘要

The surface ligands on-colloidal nanocrystals (NCs) play an important role in the performance of NC-based optoelectronic devices such as photovoltaic cells, photo-detectors, and light-emitting diodes (LEDs). On one hand, the NC emission depends critically on the passivation of the surface to minimize trap states that can provide nonradiative recombination channels. On the, other handy the electrical properties of NC films are dominated by :the ligands that constitute the barriers for charge transport from one NC to its neighbor. Therefore, surface modifications via ligand exchange have been employed to improve the conductance of NC films. However, in LEDs, such surface modifications are more critical because of their possible detrimental effects-on the emission properties: In this work, we study the role of surface ligand modifications on the optical and electrical properties of CdSe/CdS dot-in-rods (DiRs) in films and investigate their performance in all-solution-processed LEDs. The DiR films maintain high photoluminescence quantum yield, around 40-50%, and their electroluminescence in the LED preserves the excellent color, purity of the photoluminescence. In the LEDs, the ligand exchange boosted the luminance, reaching a fourfold increase from 2206 cd/m(2) for native surfactants to 8500 cd/m(2) for the exchanged aminoethanethiol (AET) ligands. Moreover, the efficiency roll-Off, operational stability, and shelf life are significantly improved, and the external quantum efficiency is modestly increased from 5.1 to 5.4%. We relate these improvements to the increased conductivity of the emissive layer and, to the better charge balance of the electrically injected carriers. In this respect, we performed ultraviolet photoelectron spectroscopy (UPS) to obtain a deeper insight into the band alignment of the LED structure. The UPS data confirm similar flat-band offsets of the emitting layer to the electron and hole-transport layers in the case of AET ligands, which translates to more symmetric barriers for charge injection of electrons and holes. Furthermore, the change in solubility of the NCs induced by the ligand exchange allows for a layer-by-layer deposition process of the DiR films, which yields excellent homogeneity and good thickness control and enables the fabrication of all the LED layers (except for cathode and anode) by spin-coating.
机译：表面配体在胶体纳米晶体（NCS）中在诸如光伏电池，光检测器和发光二极管（LED）的NC基光电器件的性能中起重要作用。一方面，NC发射尺寸统治性地取决于表面的钝化，以最小化可以提供非阵列重组通道的陷阱状态。在此方面，其他方便的NC膜的电性能由：构成从一个NC到邻居的电荷输送障碍的配体。因此，已经采用了通过配体交换的表面修饰来改善NC膜的电导。然而，在LED中，由于它们可能的不利影响 - 对发射性能的影响更为严重：在这项工作中，我们研究了表面配体修饰对CDSE / CDS点杆的光学和电性能的作用（DIRS）在电影中，并调查它们在全解决方案处理的LED中的性能。 DIR膜保持高光致发光量子产率，约40-50％，并且其电致发光在LED中保持优异的色彩，纯度的光致发光。在LED中，配体交换促进亮度，从2206cd / m（2）增加到10206cd / m（2）的四倍，以进行10500cd / m（2）的交换的氨基乙醇（aet）配体。此外，效率滚降，操作稳定性和保质期得到了显着改善，外部量子效率从5.1增加到5.4％。我们将这些改进与发光层的电导率增加，以及电气注入载体的更好的充电平衡。在这方面，我们进行了紫外线光电子谱（UPS），以获得更深的洞察LED结构的带对准。 UPS数据在AET配体的情况下确认发光层的与电子和空穴传输层相似，这转换到电荷注入电子和孔的更具对称屏障。此外，由配体交换诱导的NCs的溶解度的变化允许逐层沉积过程的DIR膜，其产生优异的均匀性和良好的厚度控制，并且能够制造所有LED层（阴极除外）和阳极）通过旋涂。

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