文章概要#

本研究开发了一种新型无机-有机杂化发光材料系统，将铯铅溴钙钛矿量子点（$\text{CsPbBr}_3$ QD） 与具有聚集诱导发光（AIE）效应的分子TBBA巧妙结合。利用钙钛矿量子点的强光吸收特性作为“天线”，以近乎100%的极高效率与43.1皮秒的超快速度将激子能量转移至AIE分子。这种机制成功避开了有机分子的紫外光降解与钙钛矿的热积累，实现了接近100%的荧光量子产率（PLQY） 以及在户外太阳光照下长达1800天的有效半衰期。研究团队还展示了该材料在大面积发光太阳能集中器（LSC）中的卓越应用潜力。

引言#

无机钙钛矿量子点与聚集诱导发光发光体作为两类备受瞩目的发光材料，在光电器件与生物成像等领域展现出巨大前景。然而，这两类材料各自存在致命的短板。钙钛矿量子点虽然色纯度高且发光效率较好，但其较软的晶格容易在持续光照下产生热降解，难以兼顾长期光稳定性与近乎完美的发光效率。有机AIE分子虽然能够有效抑制浓度猝灭，但在紫外光照射下极易产生自由基或单线态氧，进而遭受严重的氧化与化学键断裂降解，且其固态下的发光量子产率通常距离100%仍有较大差距。为了攻克这一双重瓶颈，研究团队提出了一种利用界面耦合效应将两者优势互补的全新杂化设计策略。

Fig.1 (a) Chemical structures and cartoon illustrations of CsPbBr3 (CPB, a perovskite quantum dot), TBBA (a luminogen with aggregation-induced emission, or AIEgen), oleic acid (OA, a QD ligand), and CPB–TBBA (an inorganic-organic hybrid). Note: In the CPB–TBBA hybrid material, TBBA molecules replace the native OA ligands on the QD surface and are anchored onto the QD surface as individual molecules through coordination interactions between the carboxyl groups and surface Pb sites. (b–d) Absorption (left, black line) and emission (right, colored line) spectra of (b) CPB in hexane, (c) TBBA in a THF/hexane mixture (fH = 90%), and (d) CPB–TBBA in hexane; insets: fluorescence photos taken under UV excitation (365 nm).

主要实验及结论#

研究人员首先合成了尺寸约3.5纳米的蓝光发光材料$\text{CsPbBr}_3$量子点以及黄光发光材料TBBA分子。羧基官能团作为天然的锚定基团，能够强烈配位在钙钛矿量子点的表面铅位点上，替代原有的油酸配体。核磁共振氢谱与傅里叶变换红外光谱实验共同证实，TBBA分子以单分散的形式成功锚定在量子点表面，而非形成游离的聚集体。杂化材料吸收光谱呈现出两者的叠加特征，但在紫外光激发下，量子点自身的蓝光发光被完全淬灭，取而代之的是来自TBBA的高亮度黄光发射，这初步预示了极其高效的界面能量转移。

为了深入揭示这种高效能量转移的微观物理过程，研究团队利用超快飞秒瞬态吸收光谱进行了实时追踪。当选择性激发钙钛矿量子点时，量子点位于455纳米处的激子漂移信号迅速衰减，同时在600至750纳米波段快速产生了属于TBBA单线态的激发态吸收特征。动态动力学拟合表明，量子点激子的寿命从纯量子点的3.7纳秒骤降至杂化体系中的42.6皮秒，证实能量转移速率高达每秒$2.32 \times 10^{10}$，能量转移效率达到惊人的99%。这种超快过程是由Förster协同Dexter能量转移机制共同驱动的。

Fig.2 (a,b) Two-dimensional pseudo-color TA spectra of (a) CPB and (b) CPB–TBBA following excitation by a 360 nm pulse. Superimposed plots in panels (a) and (b) are the TA spectra at delay times of 100 ps and 1 ns, respectively. (c) Two-dimensional pseudo-color TA spectrum of CPB–TBBA following excitation by a 500 nm pulse. The superimposed plot is the TA spectrum at a delay time of 100 ps. (d) Kinetics of CPB exciton probed at 455 nm (CPB*, orange) and the TBBA singlet probed at 660 nm (TBBA*, red) in CPB–TBBA, respectively (data taken from plot B); kinetics of CPB* in free CPB (blue) shown for comparison (data taken from plot A); λex = 360 nm. Time-resolved PL kinetics of CPB–TBBA (yellow) probed at 570 nm; λex = 405 nm.

在光物理性能提升方面，锚定在量子点表面的TBBA分子受到了周围长链配体环境的强烈空间限域，其分子内旋转与振动运动被大幅限制。这种限制作用将非辐射复合速率降至最低，使得杂化体系表现出高达接近100%的荧光量子产率。此外，由量子点吸光并转移给TBBA发光的双组分机制，使杂化材料产生了高达4523波数的巨大有效斯托克斯位移，相比纯量子点增大了近10倍。巨大的斯托克斯位移将材料的自吸收因子从0.44大幅削减至0.004，极大地降低了光子在传播过程中的重吸收损失。

Fig.3 (a) Photoluminescence (PL) spectra of TBBA in hexane/THF mixtures with different volumetric fractions of hexane (fH); c = 19.5 µM. (b) Relative PL intensities (I/I0) and PL peaks (λ) at varying fH; I0 represents the PL intensity in the THF solution (fH = 0). (c) Radiative (red) and nonradiative (black) rates of TBBA under different fH in the THF solution (blue region) and CPB–TBBA in hexane (red region). (d) PL spectrum of CPB–TBBA hybrid; those of CPB quantum dot and TBBA film are shown for comparison by dotted lines. (e,f) Stokes shifts and reabsorption for CPB, TBBA, and CPB–TBBA. Note: the data for TBBA are measured in the hexane/THF mixtures (fH = 90%).

光稳定性测试进一步展示了该杂化材料的巨大优势。在模拟太阳光强36倍的高功率氙灯持续照射下，常规有机荧光染料与游离TBBA分子在十几小时内便完全褪色，纯钙钛矿量子点薄膜也在60小时后出现明显的变黑与光热分解。然而，杂化材料薄膜在经过长达100小时的超强照射后，发光强度几乎没有衰减，保持了极高的光化学稳定性。折算为户外实际太阳光照条件，杂化材料的有效发光半衰期长达1800天。这种优异的光稳定性源于量子点作为光天线吸收了有害的紫外光子，同时超快能量转移迅速抽离了量子点的激发态能量，避免了局域热积累。研究团队将该杂化材料集成到大面积发光太阳能集中器（LSC）器件中，展现出了远超传统材料的线型光收集效率与高功率输出。

Fig.4 (a) Photographs of coumarin 343 (C343) in ethanol, TBBA in THF, and TBBA in a hexane/THF (H/T) mixture (fH = 80%) under the irradiation of a xenon lamp at a power density of 1.08 W/cm2; the interval between each photo is 5 h. (b) Photographs of TBBA, CPB and CPB–TBBA films in a polybutadiene (PBD) matrix under the irradiation of the xenon lamp for given periods of time; the interval between each photo is 10 h. (c) Dependence of PL intensity of the luminescent materials on the irradiation time by the xenon lamp, which was converted to effective outdoor exposure time by a factor of 3.6. (d) Photostability of the luminescent materials: I, C343 solution, II, TBBA solution, III, TBBA aggregate in the H/T mixture, IV, CPB film, V, TBBA film, VI, CPB–TBBA film. (e,f) Comparisons of (e) photoluminescence quantum yield (PLQY) and (f) Stokes shift of the CPB–TBBA film with those of the previously reported luminescent solar concentrator (LSC) materials. Luminescent materials in (e): I, Cy7, II, CdSe/CdS QD, III, Si QD, IV, PbS/CdS QD, V, C-dots, VI, DCJTB/Pt(TPBP), VII, CuInSe2/ZnS QD, VIII, TPA-BT, IX, CPB–TBBA; luminescent materials in (f): I, CPB, II, Cy7, III, PbS/CdS QD, IV, Si-QD, V, C-dots, VI, TBBA, VII, CPB–TBBA. Note: The data in plot d are obtained in this work, while those in plots e and f are directly obtained from the reported literature (Table S3).

Fig.5 (a) Normalized absorption spectrum of CPB–TBBA (blue), solar spectrum (red), and photopic vision (yellow) in the visible spectral range of 350–750 nm. (b) Plot of solar absorptance (ηabs) versus visible transmittance for the films of CPB–TBBA in the PBD matrix at different concentrations; inset: photographs of the films taken under ambient lighting conditions. (c,d) Photographs of a square-shaped LSC film (5.2 cm ✗ 5.2 cm) taken under (c) outdoor conditions and (d) 365-nm illumination in the darkroom. (e,f) Comparison of (e) internal (ηint) and (f) external optical efficiencies (ηext) of the CPB–TBBA LSC with those of the previously reported LSC materials: I, Cy7, II, CdSe/CdS QD, III, Si QD, IV, PbS/CdS QD, V, C-dots, VI, CuInSe2/ZnS QD, VII, TPA-BT, VIII, CPB–TBBA. Note: The data in plots e and f are directly obtained from the reported literature (Table S3).

总结及展望#

这项研究成功构建了一种高稳定性与高发光效率兼得的钙钛矿量子点与AIE分子杂化系统。通过界面化学工程与超快动力学调控，不仅解决了有机分子易光解和无机量子点易热降解的行业痛点，还实现了接近极限的光学性能。该工作引入的无机-有机界面协同调控策略具有高度的普适性，不仅为设计长寿命、高亮度的杂化发光材料树立了新标杆，更为未来大面积太阳能光伏集中技术、固态照明及下一代显示器件的产业化应用开辟了广阔的前景。