ADVANCED NEAR-INFRARED PHOTODETECTORS BASED ON LEAD SULFIDE QUANTUM DOTS

基于硫化铅量子点的高性能红外光电探测器

Tang HD(唐浩东)

11756025

博士

机械工程

工学博士

孙小卫

Carl Anthony, Zoe Pikramenou

2021-09-28

2021-12-31

伯明翰大学

英国

This thesis investigated an advanced material: lead sulfide (PbS) quantum dots (QDs), designed, optimized and performed different strategies to enhance the performance of near-infrared (NIR) photodetectors based on PbS QDs. Previous researchers have performed some great studies suggesting that PbS QDs have great potential in NIR detection and photovoltaic area. Compared with traditional semiconductor bulk materials, the QD materials could have wide, adjustable absorption band, which enables long range detection of light through ultraviolet to infrared, covering entire visible light. Compared with another popular material in optoelectrical area, perovskite materials, PbS QDs showed its advantage in stability and NIR detection. Though, it has been 15 years since PbS QDs first been used for NIR detection, there are still a long way from the PbS QD photodetectors (PDs) to the commercial applications.Thus, in this thesis, three different technologies are used to optimize the overall performance of PbS QD PDs. Considered of the low carrier extraction efficiency in PbS QD solids, a two-step ligand exchange process is introduced to further exchange the OA- ligands with I- ligands, which could reduce the inner separation between QDs. This two-step ligand exchange technology would cause a more compact stacking behavior of QDs and result in a higher carrier extraction efficiency, which finally reveal to an enhanced responsivity of the fabricated device. Furthermore, the deposition method for PbS QDs is also investigated. By comparing spray-coating technology with traditional spin-coating technology, spray-coated PbS QD PD showed an enhanced responsivity. The enhancement is mainly related to the more compact stacking of PbS QDs, which is confirmed by grazing-incidence small-angle X-ray scattering (GISAXS) analysis. Longer time during the film formation, the PbS QDs would have higher chance to form a self-assembled body-centered cubic (BCC) structure, rather than the distorted superlattice situation in the spin-coated QD solid. Similarly, this enhancement is also brought by reduced inner separation between PbS QDs.On the other hand, a new structure for NIR detection and display at the same time is proposed by stacking a light-emitting diode (LED) onto the PD. The PD works as a NIR controlled light switch, only under the illumination of NIR light, the LED device could work normally. Otherwise, even there is strong bias voltage, the LED will not be turned-on. This is achieved by well designed energy bands in this device. The injected carriers are blocked by the carrier blocking layers, then the circuit is connected by the photogenerated carriers produced in PD structure when the device is illuminated by NIR light. The device could be regarded as a up-converter which absorbs NIR light and emit red light. Also, the device could be considered as a NIR photodetector which introduced excess carriers from the circuit during the illumination of NIR light.Eventually, these methods have enhanced the performance of PbS QD PDs. However, the problems of stability, large area fabrication, cost and packaging should be solved before the commercial or industrial applications based on PbS QD PDs could be realized.

本论文研究了一种先进材料：硫化铅 (PbS) 量子点 (QD)，设计、优化并执行了不同的策略，以提高基于 PbS QD 的近红外 (NIR) 光电探测器的性能。以前的研究人员已经进行了一些伟大的研究，表明 PbS QD 在 NIR 检测和光伏领域具有巨大的潜力。 与传统的半导体块体材料相比，QD材料具有较宽、可调节的吸收带，可以实现从紫外到红外的远距离检测，覆盖整个可见光。 与光电领域的另一种流行材料钙钛矿材料相比，PbS QDs 在稳定性和 NIR 检测方面表现出优势。 尽管 PbS QD 首次用于 NIR 检测已有 15 年，但从 PbS QD 光电探测器 (PD) 到商业应用还有很长的路要走。因此，在本论文中，使用三种不同的技术来优化 PbS QD PD 的整体性能。考虑到 PbS QD 固体中载流子提取效率低，引入两步配体交换过程以进一步交换 OA-配体与 I-配体，这可以减少 QD 之间的内部分离。这种两步配体交换技术将导致量子点更紧凑的堆叠行为，并导致更高的载流子提取效率，最终揭示出所制造器件的响应性增强。此外，还研究了 PbS QD 的沉积方法。通过比较喷涂技术与传统旋涂技术，喷涂 PbS QD PD 显示出增强的响应度。这种增强主要与 PbS QD 的更紧凑堆叠有关，这通过掠入射小角 X 射线散射 (GISAXS) 分析得到证实。在成膜过程中更长的时间，PbS QDs 将有更高的机会形成自组装体心立方 (BCC) 结构，而不是旋涂 QD 固体中扭曲的超晶格情况。同样，这种增强也是由 PbS QD 之间减少的内部分离带来的。另一方面，通过将发光二极管 (LED) 堆叠到 PD 上，提出了一种同时用于 NIR 检测和显示的新结构。 PD作为NIR控制的光开关，只有在NIR光的照射下，LED器件才能正常工作。否则，即使有很强的偏置电压，LED 也不会点亮。这是通过该设备中精心设计的能带实现的。注入的载流子被载流子阻挡层阻挡，然后当器件被近红外光照射时，PD结构中产生的光生载流子连接电路。该器件可以看作是吸收近红外光并发出红光的上变频器。此外，该器件可以被视为 NIR 光电探测器，它在 NIR 光照射期间从电路中引入多余的载流子。最终，这些方法增强了 PbS QD PD 的性能。然而，在实现基于 PbS QD PD 的商业或工业应用之前，需要解决稳定性、大面积制造、成本和封装等问题。

Quantum dot photodetector ligand exchange carrier lifetime inner dot distance

量子点 光电探测器 配体置换 载流子寿命 量子点间距

英语

联合培养

南方科技大学

Tang HD. ADVANCED NEAR-INFRARED PHOTODETECTORS BASED ON LEAD SULFIDE QUANTUM DOTS[D]. 英国. 伯明翰大学,2021.