胶体量子点因其光谱窄、可见光范围内颜色可调、优异的溶液可加工性等优势，成为发光二极管（LEDs）中有前景的发光材料。相较于各向同性的量子点，一维纳米棒凭借其二维量子限域结构，展现出沿长轴的线性偏振发射和更快的辐射复合速率等附加优势，可显著提高LEDs的外量子效率与发光亮度。然而，纳米棒增大的表面积也增加了表面陷阱态和俄歇复合的概率，导致其光致发光量子产率通常低于各向同性量子点。此外，在从溶液到薄膜的转化过程中，发光内核的聚集及能量转移损耗会进一步降低器件性能。为实现溶液可加工纳米棒向功能性固态薄膜的转化，通常需要生长保护性壳层。这种核/壳结构能有效钝化发光核的表面缺陷、抑制核间聚集与福斯特共振能量转移，并实现高效的载流子限域。通过种子生长法进行外延壳层生长已被广泛研究，但由于明显的晶面依赖性生长动力学，在纳米棒上实现各向异性的壳层生长仍是一个重大的合成挑战。
传统有机磷配体通过快速注入法合成的核/壳纳米棒，由于配体在垂直于长轴的晶面上具有高结合力，表现出高度各向异性壳层生长。这种优先结合导致纳米棒沿长轴过度生长而短轴覆盖不足，所形成的高长径比、薄壳层纳米棒在旋涂成膜时易出现无序堆叠和聚集，从而降低光取出效率，同时增加漏电流和能量转移。已有研究发现具有厚壳层和低长径比的纳米棒有利于提高薄膜均匀性与光取出效率，并抑制漏电流和能量转移。通过慢注入法控制壳层生长已被证明能有效增加径向壳层厚度并降低长径比。尽管已有这些进展，如何在纳米棒领域实现均匀的厚壳层生长同时保持低长径比，仍是未解决的难题。
除了控制均匀厚壳生长，调控壳层的组分与结构对于降低界面晶格失配、增强载流子限域，从而提升纳米棒光电器件性能同样至关重要。与各向同性量子点相比，各向异性纳米棒在壳层生长过程中因强烈的晶面依赖性反应活性而表现出更显著的界面应变，限制了壳层材料的选择并增加了组分与结构调控的复杂性。
为克服这些挑战，北京理工大学李红博等人提出了一种双配体（有机磷/羧酸）慢注入策略，成功实现了以纤锌矿ZnSe为主的组分连续梯度厚壳层（CdZnSe/ZnSeS）生长。有机磷配体提供了高单体浓度的生长环境，促进了各向异性壳层生长；而羧酸配体在不同晶面上表现出相近的结合能，有利于壳层各向同性生长。这不但增加了纳米棒的径向厚度，也解决了因晶面动力学差异导致的沿长轴过度生长和短轴覆盖不足的问题。制备的核/壳纳米棒表现出接近统一的光致发光量子产率和0.67的线性偏振比。它们通过薄膜制备工艺形成了致密、近乎单层的纳米棒发光薄膜，并平行于基底排列，实现了接近85%的面内跃迁偶极矩取向分布，从而最大限度地减少了漏电流和福斯特共振能量转移，并提高了光输出耦合效率。将其应用于电致发光器件后，结果实现了32.0%的外量子效率和超过1.1×106 cd m⁻²的峰值亮度，并在1,000 cd m⁻²亮度下表现出超过6.8×104小时的优异T95工作寿命。这项研究不仅攻克了各向异性纳米棒难以均匀生长梯度厚壳的合成难题，更通过材料结构的精准设计，同步优化了发光效率、偏振特性、薄膜形态与载流子注入平衡，从而建立了梯度厚壳胶体纳米棒作为面向高效、稳定与偏振光电子器件的可推广材料平台。
二、结果
Fig.1|Influence of NR shell structure on their morphology and optoelectronic properties. aSchematic diagram of the arrangement of spin-coating films of thin-shell NRs with high aspect ratio and thick-shell NRs with low aspect ratios on the hole transport layer (HTL). The spin-coating film of thin-shell NRs with high aspect ratio is more prone to generate out-of-plane emission, FRET and leakage current, while the spin-coating film of thick-shell NRs with low aspect ratio is more prone to generate in-plane emission, and suppress FRET and leakage current.bIllustration of the band alignment for bulk CdSe, ZnSe, ZnS and CdS, energy-level schematics and electron/hole wavefunctions of CdSe/CdZnSe/ZnSeS core/shell NRs.cSchematic illustrations of the synthesis of CdSe NRs and CdSe/CdZnSe/ZnSeS NRs.dThe binding energies of oleic acid on (001) and (100) facets of CdSe NRs.eTEM image of CdSe/CdZnSe/ZnSeS NRs (the imaging was performed on n = 5 independently synthesized batches resulted in identical morphology and size).fX-ray diffraction patterns for CdSe NRs and CdSe/CdZnSe/ZnSeS NRs.gThe EDS line scanning image of a CdSe/CdZnSe/ZnSeS NR. Source data are provided as a Source Data file.
Fig.2|Optical characterizations of CdSe/CdZnSe/ZnSeS core/shell NRs.aAbsorption and PL spectra of core and core/shell NRs. Inset is a photograph of the core/shell NRs solution.bTRPL dynamics of core and core/shell NRs.cBiexciton recombination kinetics can be fitted by single-exponential decay with a lifetime of 1246 ps. Inset is the pump fluence-dependent kinetics.dPL blinking traces and corresponding intensity distribution histogram of the core/shell NR.ePolarization-dependent PL emission intensity as a function of the angle relative to NR long axis. Source data are provided as a Source Data file.
Fig.3|Influence of thin- and thick-shell NRs onluminescent layer qualityandNR-LED operation.aSchematics of the arrangement of different NRs in film.bAFM andcSEM imagesof spin-coated thick-shell and thin-shell NR films on HTL (the imaging was performed on n = 5 independently prepared films, SEM images of thick-shell NRs showed uniform films, SEM images of thin-shell NRs showed disordered films).dDevice structure of NR-LEDs.eCross-sectional TEM image of thick-shell NR-LEDs with HR-TEM (the imaging was performed on n= 5 independently prepared NR-LEDs, SEM images of NR-LEDs showed consistent thickness of each functional layer), EDS elemental mapping for Cd, and diffraction patterns of the luminescent layer.fPL mapping of thick-shell NR film spin-coated on HTL.gBFP imaging of thick-shell NR film spin-coated on HTL with comparison between simulated (85% horizontal dipoles) and experimental line cuts.hCurrent density-voltage curves of thin- and thick-shell of NR-LEDs. Insets: schematics of rough and uniform NR films.iSurface temperature evolution under different voltages for the thin- and thick-shell NR-LEDs. Insets shows infrared images of the two devices at working under 7 V, respectively. The scale bar is 1 cm. Source data are provided as a Source Data file.
Fig.4| Characterizations of CdSe/CdZnSe/ZnSeS core/shell NR-LEDs. a EL spectra under different driving voltages (3-10 V). Inset shows the corresponding CIE coordinates (0.657-0.669, 0.321-0.328). b Current density and luminance versus voltage. Inset shows a photograph of a working NR-LEDs emitting uniformly over the entire device area. c EQE and current efficiency versus luminance. Inset shows a photograph of four NR-LED pixels. d Comparison of peak EQE with previously reported values14,30,31,36,37,48-54. e Comparison of maximum luminance with previously reported values14,29-31,36,48,55-57. f Operational lifetime and driving voltage versus time. g Comparison of T95 operation lifetime at an initial luminance of 1000 cd m-2 with previously reported values13,14,30,47,53,55,58. Source data are provided as a Source Data file.
Fig.5|Comparing of thick-shell NR-LEDs and thin-shell NR-LEDs.a-bCurrent density-voltage-luminance characteristic and luminance-EQE characteristic curves of CdSe/CdZnSe/ZnSeS NR-LEDs with 2000 consecutive voltage scans from 0 to 4 V.cSchematics comparing the carrier injection and recombination processes of CdSe/CdZnSe/ZnSeS thick-shell NR-LEDs and CdSe/CdS thin-shell NR-LEDs. The gradient alloy shell is beneficial for balancing carrier injection and suppressing electron leakage, while thin shell is prone to electron capture by defects and electron leakage.d-eEL spectra of CdSe/CdZnSe/ZnSeS thick-shell NR-LEDs and CdSe/CdS thin-shell NR-LEDs under different driving voltages, and the inset shows the parasitic emission from HTL (TFB).fSurface temperature evolution of thin-shell NR-LEDs (top) and thick-shell NR-LEDs (bottom) under a constant current density of 50 mA cm-2. The upper and lower insets show their infrared thermal images. The room temperature is 20.8 °C, and the scale bar is 1 cm. Source data are provided as a Source Data file.
三、原文链接
Selective radial thickness growth of compositionally graded shells on colloidal quantum rods for more efficient light-emitting diodes
Yicheng Zeng, Xiaonan Liu,Duanyang Liu, YuanLiu, Qingya Wang, Weiwei Chen, Jing Wei, Jian Xu, Fangze Liu, Hongbo Li*
Nature Communications (2026)
Zeng, Y., Liu, X., Liu, D. et al. Selective radial thickness growth of compositionally graded shells on colloidal quantum rods for more efficient light-emitting diodes. Nat Commun (2026). https://doi.org/10.1038/s41467-026-73298-4
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