欧洲杯

量子点发光二极管（QLED）作为新一代显示与照明技术的关键器件，正引起学术界与产业界的高度关注。随着研究的深入，QLED凭借其快速光响应能力与可调发光特性，可实现光学写入、读取以及多级编码的功能，具备集成传感、存储与显示功能的潜力。而QLED实现写入/读取功能的核心在于电荷的有效存储与载流子的积累、提取以及再复合过程。因而，实现其类存储器功能的关键在于对电荷储存及后续提取复合行为的有效调控。因此，深入理解并调控其内部的载流子动力学过程尤为关键。

近日，吉林大学纪文宇教授和张汉壮教授等人制备了基于Cu-In-Zn-S（CIZS）量子点的电子发光器件，并系统地探究了影响其空穴储存的关键因素，通过瞬态电致发光（TrEL）和瞬态光致发光（TrPL）等表征，揭示了基于CIZS量子点器件中的电荷分布及工作机理。研究表明，在脉冲电压的激励下，该器件的TrEL响应在上升沿与下降沿分别表现出显著的电致发光过冲和尖峰现象，这一独特特征源于器件内部的电荷存储效应。该性能的获得主要归因于两方面：其一，CIZS量子点中Cu相关缺陷态能级形成局域态，有效延长了空穴驻留的时间；其二，合理的器件结构设计进一步强化了空穴限制效应，即选用更深HOMO能级的BCBP作为空穴传输层（HTL）抑制空穴回迁，同时在HTL中插入约为3 nm厚的PPT薄层，利用其较低的LUMO能级和自发取向极化特性，能够有效俘获泄漏的电子，从而进一步提升器件的空穴存储。此外，该文章还系统探讨了器件中电荷存储效应对脉冲驱动参数的依赖关系及其影响机制。研究发现，适当延长脉冲驱动时间（t_w）及提高反向驱动电压（V_R）有助于增强量子点中空穴的存储效应与剩余载流子的提取效率，从而显著提升器件的“读取”能力。基于该独特特性，本文构建了一种基于常规QLED的写入–读取工作模式。器件实现了长达0.8秒的空穴存储时间，为QLED开辟新的工作模式和应用前景，特别是在防伪识别等对高密度存储与响应延迟具有特殊需求的场景中展现出潜力。相关成果以“Second-Scale Hole Storage in Electrically Driven Multinary Quantum Dots”为题目，发表在Nano letters期刊上。

论文链接：

//pubs.acs.org/doi/full/10.1021/acs.nanolett.5c03663

Figure 1. Illustration of charge carrier distribution and transport within a QLED. (a) Injection, (b) discharging, (c) residual charges (hole storage). (d) Electron leakage and (e) electron capturing during device operation. (f) Delayed EL emission under a reverse voltage. Holes are captured by the Cu-mediated states and then recombine with the electrons. ETL, HTL, and EML represent electron transport layer, hole transport layer, and emission layer, respectively.

Figure 2. (a) Flat energy levels of materials used in this work. (b) J–V–L, (c) EQE–J, and (d) EL spectra of QLEDs with and without PPT electron-capturing unit.

Figure 3. (a) Whole TrEL response of QLED with PPT, driven under a voltage pulse with frequency of 1000 Hz, Vw = 4.0 V, tw = 400 µs, VR = 0 V. Falling edges of TrEL response of PPT-containing QLED with (b) various Vw and (c) VR. The EL intensity is normalized according to the steady-state intensity during the on-period. The ts = 0 for the above measurements. Illustration of the charge distribution within the device under (d) low and (e) high driving voltage.

Figure 4. EL spike of the QLED at various (a) driving durations, tw and (b) standby voltage Vs. All the signals are recorded at ts = 1000 µs. (c) EL spike of the QLED at different times after turning off the driving voltage, ts.

Figure 5. Modelling of the write-read process. (a) Drive voltage waveform. (b) Single write-read cycle. (c) Read operations at varying time delays under identical write conditions.

欧洲杯 博士生朱炳焱为本文的第一作者，本文通讯作者为欧洲杯 张汉壮教授，纪文宇教授，该工作得到了国家自然科学基金项目的资助和吉林省科技厅项目的支持。