PbSe/PbS核壳量子点近红外LED的研究

RESEARCH ON NEAR INFRARED LIGHT-EMITTING DIODES BESED ON PBSE/PBS CORE/SHELL QUANTUM DOTS

钟华英

11849046

硕士

光学工程

孙小卫

2020-05-28

2020-07-08

哈尔滨工业大学

深圳

近红外发光二极管在医疗，军事和通信等领域都有广泛的应用，而胶体量子点作为近红外的发光材料具有其独特的优势，比如在溶液中的荧光量子产率高、粒径可调节的吸收和发射光谱、可在任意基板成膜并适用于喷墨打印等批量生产技术等等。本文的研究对象是基于PbSe/PbS核壳量子点的近红外发光二极管，研究内容聚焦在发光二极管的量子点发光层，研究内容包括PbSe/PbS核壳量子点的合成，量子点薄膜的载流子传输效率的优化以及量子点表面缺陷的钝化等三个方面。具体内容和相关结果如下：PbSe量子点在空气中容易受水氧的侵蚀而造成其稳定性差，通过在PbSe量子点的表面包覆厚度大于1nm的PbS壳层作为其发光中心的保护层，试图延缓PbSe量子点的氧化过程。在PbSe量子点的壳层生长中，利用双泵来分别调节Pb和S两种前驱体的注入比例，并控制壳层生长的反应时间和温度等条件获得目标壳层厚度。其中，通过提高壳层前驱体溶液的Pb：S摩尔比和PbSe浓度来避免PbS成核而引起发射光谱的双峰现象。为检验PbS壳层对PbSe量子点的稳定性提高的有效性，将甲苯溶液中的PbSe量子点和PbSe/PbS核壳量子点放置在空气下测量连续三天内的吸收光谱，对比发现PbSe/PbS核壳量子点的抗氧化能力并不明显，光谱的蓝移速率甚至更快。另外，与PbSe量子点相比，PbSe/PbS核壳量子点的荧光寿命增加，荧光量子效率有所降低。在量子点薄膜的载流子传输方面，通过固态配体交换的方式将PbSe/PbS核壳量子点表面的长碳链油酸配体替换成短碳链的8-巯基辛酸配体来缩短量子点间距，从而增加量子点之间的电子耦合效率和电荷载流子的传输效率。利用8-巯基辛酸配体交换后的薄膜来制备发光二极管，器件在发光峰值1280nm的位置得到最大的辐亮度是0.65Wsr-1m-2、外量子效率的平均值和最大值分别为0.60.26%和1%。在量子点的表面缺陷方面，在8-巯基辛酸配体交换完成后，利用原子配体来进一步钝化量子点的表面缺陷态。通过CdCl2溶液对8-巯基辛酸配体交换完成后的量子点薄膜进一步采用固态配体交换的方式完成量子点表明缺陷的钝化。由于有机短碳链配体无法充分覆盖量子点表面，并且交换后的量子点的化学稳定性变差，所以需要原子配体来填充未被覆盖的量子点表面缺陷。使用了8-巯基辛酸配体和CdCl2配体依次交换的量子点薄膜制备相同器件结构的发光二极管，在相同的发光峰值处，器件的最大辐亮度提升至0.95Wsr-1m-2、外量子效率的平均值和最大值分别为0.730.52%和1.3%。另外，与单纯的8-巯基辛酸配体相比，依次使用8-巯基辛酸配体和CdCl2配体交换的量子点薄膜器件的开启电压从5V降至4V，击穿电压从8V升至9V。

Near-infrared light-emitting diodes have a wide range of applications in medical, military, and communications fields. Colloidal quantum dots (QDs) provide unique opportunities as NIR emitters due to their advantages, such as high photoluminescence efficiency (PLQE) in solution and size-tunable emission combined with convenient, low-cost, solution-based integration on any substrate using utilizing effective mass production methods including inkjet printing.PbSe QD based NIR LEDs are the research object of this dissertation. The research content mainly focuses on the stability of PbSe QDs, carrier transport in QD films, and defect passivation for QDs to optimize the key parameters of NIR LEDs performance. The specific research content and related results are as follows:Regarding the instability of PbSe QDs PbSe QDs are covered with the PbS shell thickness greater than 1nm, which is used as a protective layer to try to delay the oxidation process of PbSe QDs in ambient environment. In the process of shell growth for PbSe QDs, the molar ratio between Pb and S adjusted by the two respective precursors injection of double pump, reaction time and temperature are together controlled to achieve the PbSe/PbS core/shell QDs with desired shell thickness. Among them, the double emission peak induced by PbS nucleation can be resolved by increasing the Pb/S molar ratio and concentration of PbSe QDs. To test whether PbS shell can effectively improve the stability of PbSe QDs, PbSe QDs and PbSe/PbS core/shell QDs in toluene solution were measured in the air to obtain changes of absorption spectrum in three days, and it turn out that the surface PbS shell of PbSe/PbS core/shell QDs cannot effectively prevent the blue shift of the spectrum under more than one day of air exposure. In addition, compared to PbSe core QDs, the fluorescence lifetime of PbSe/PbS core/shell QDs is longer, and photoluminescence quantum efficiency is lower.As for the carrier transport efficiency in QDs film, the long carbon chains of oleic acid on the surface of as-synthesized PbSe/PbS core/shell QDs were replaced with substituted 8-hexyloctanoic acid ligands by means of solid-state ligand exchange. The maximum radiance obtained by the device at the light emission wavelength of 1280nm is 0.65Wsr-1m-2, and the average and maximum of external quantum efficiency (EQE) is 0.6±0.26% and 1%, respectively.In terms of the trap states of QDs, the CdCl2 solution was used to passivate the surface defects of QDs film after the ligand exchange of short carbon chains(8-hexyloctanoic acid, MOA) was completed. Since the surface coverage of the short carbon chains on QDs is inefficient and the chemical stability of QDs is deteriorated, further atomic ligand exchange was used to fill the surface traps of QDs. QDs film with MOA/CdCl2 ligands were used to prepare LEDs with the same device structure. At the same emission wavelength, the maximum radiance of the device was increased to 0.95Wsr-1m-2, and the average and maximum of EQE is 0.73±0.52% and 1.3%, respectively. In addition, with the pure treatment of 8-hexyloctanoic acid ligands, the turn-on voltage of QD based NIR LEDs where MOA/CdCl2 ligands treated QDs film based NIR LED’ turn-on voltage varied from 5V to 4V, and its breakdown voltage has been increased from 8V to 9V.

近红外发光二极管 PbSe/PbS核壳量子点 核壳结构 配体交换

near-infrared light-emitting diodes PbSe/PbS core/shell quantum dots core/shell structure surface ligand exchange

中文

联合培养

南方科技大学

钟华英. PbSe/PbS核壳量子点近红外LED的研究[D]. 深圳. 哈尔滨工业大学,2020.