Inorganic shelling is a key strategy to address unwanted, surface-mediated nonradiative pathways in semiconductor nanocrystals. Improved passivation particularly advances the use of the smallest nanocrystals because complex photophysics arise as nanomaterials approach the molecular limit. However, shelling strategies developed for larger/more-robust nanocrystals are not always applicable in this size regime. Herein, we introduce the direct synthesis of ultrasmall (ø < 2 nm) PbS nanocrystals shelled with a range of metal-halide-perovskite-like monolayers by employing the appropriate two-dimensional perovskite as a precursor at the point of nanocrystal growth. These passivated nanocrystals possess improved photoluminescence quantum yields, reduced dynamic spectral red-shifting after photoexcitation, and longer, more-monoexponential photoluminescence dynamics─consistent with a reduction in defect-mediated exciton–phonon coupling. We then apply these shelled, ultrasmall PbS nanocrystals as sensitizers in a triplet-fusion upconversion architecture and observe 2-fold improved triplet yields. This demonstration emphasizes the photophysical benefits realized via our 2D perovskite shelling strategy, which can be applied to other nanocrystals─especially to small particles that are similarly vulnerable to existing strategies for post-synthetic modifications.

中文翻译：

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金属卤化物-类钙钛矿单层钝化超小型 PbS 纳米晶体的直接合成

无机壳是解决半导体纳米晶体中不需要的、表面介导的非辐射途径的关键策略。改进的钝化特别促进了最小纳米晶体的使用，因为当纳米材料接近分子极限时会出现复杂的光物理学。然而，为更大/更坚固的纳米晶体开发的脱壳策略并不总是适用于这种尺寸范围。在此，我们介绍了通过在纳米晶体生长时采用适当的二维钙钛矿作为前体，直接合成带有一系列金属卤化物钙钛矿类单层壳的超小（ø<2 nm）PbS纳米晶体。这些钝化纳米晶体具有更高的光致发光量子产率、减少光激发后的动态光谱红移以及更长、更单指数的光致发光动力学，这与缺陷介导的激子-声子耦合的减少一致。然后，我们将这些带壳的超小 PbS 纳米晶体用作三重态融合上转换结构中的敏化剂，并观察到三重态产率提高了 2 倍。该演示强调了通过我们的 2D 钙钛矿脱壳策略实现的光物理优势，该策略可应用于其他纳米晶体，尤其是同样容易受到现有合成后修饰策略影响的小颗粒。