表面配体修饰提高CdSe/CdS Dot-in- Rod发光二极管的性能
Enhancing the Performance of CdSe/CdS Dot-in- Rod Light Emitting Diodes via Surface Ligand Modification
摘要：
胶体纳米晶表面的配体对纳米晶基光电子器件如光电池、光电探测器和发光二极管的性能起着重要的作用。一方面，NC发射关键取决于表面的钝化，以最小化可以提供非辐射复合通道的陷阱态。另一方面，NC膜的电学性质主要由构成电荷从一个NC传输到其邻居的势垒的配体决定。因此，通过配体交换的表面改性已被用于改善NC膜的电导。然而，在发光器件中，这种表面改性由于其对发射特性的可能有害影响而更加关键。在这项工作中，我们研究了表面配体修饰对薄膜中的CdSe/CdS点棒（DiRs）的光学和电学性质的作用，并研究了它们在全溶液处理LED中的性能。DiR膜保持高PLQY，约40- 50%，并且它们在LED中的电致发光保持PL的优异色纯度。在LED中，配体交换提高了亮度，从天然表面活性剂的2200 cd/m2增加到交换的氨基乙撑乙烷配体的8500 cd/m2，达到四倍。此外，效率滚降、操作稳定性和保质期显著改善，并且外量子效率从5.1%适度增加到5.4%。我们将这些改进与发射层的导电性增加以及电注入载流子的更好的电荷平衡相关。在这方面，我们进行了紫外光电子能谱学（UPS），以获得更深层次的了解在LED结构的能带排列。
英文摘要：
The surface ligands on colloidal nanocrystals (NCs) play an important role in the performance of NCs based optoelectronic devices such as photovoltaic cells, photodetectors 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 non-radiative recombination channels. On the other hand, 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 ligandexchange have been employed to improve the conductance of NC films. However, in light emitting devices, such surface modifications are more critical due to 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 PLQY, around 40-50%, and their electroluminescence in the LED preserves the excellent color purity of the PL. In the LEDs, the ligand-exchange boosted the luminance, reaching a four-fold increase from 2200 cd/m2 for native surfactants to 8500 cd/m2 for the exchanged aminoethanethiol 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 deeper insight in the band alignment of the LED structure.
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