A typical layered hybrid perovskite, A₂PbBr₄, consists of organic A-site cations and the inorganic [PbBr₄]^2– perovskite layers. Alternatively, here the A-site cation itself is a hybrid one, namely, [(4AMTP)PbBr₂]₂²⁺, containing a nonperovskite PbBr₂ type lattice and 4AMTP (4-aminomethyltetrahydropyran cation). How does this hybrid A-site cation influence the structure and luminescence of a [(4AMTP)PbBr₂]₂PbBr₄ 2D layered perovskite? Here, we address this question by exploring crystal structure and photoluminescence (PL) in the temperature range 7–300 K. Centimeter-sized single crystals of [(4AMTP)PbBr₂]₂PbBr₄ show a stable monoclinic P2₁/c space group in the entire temperature range, without showing any phase transition. The absence of a phase transition signifies higher structural rigidity brought in by the hybrid A-site cation, unlike typical A₂PbBr₄ with organic A-site cations that often exhibit a phase transition in this temperature range. PL of [(4AMTP)PbBr₂]₂PbBr₄ at room temperature shows excitonic emissions similar to a typical A₂PbBr₄ with an organic A-cation because neither hybrid nor organic A-site cations contribute to the valence and conduction band edges. Interestingly, below 70 K, the excitonic emission suddenly red-shifts by 15 meV from 3.017 to 3.002 eV, along with an order of magnitude increase in lifetime. Similar temperature-induced PL changes in monoclinic-phase layered perovskites were previously attributed to spin-forbidden “dark” exciton emissions, which become significant at lower temperatures. The hybrid A-site cation in [(4AMTP)PbBr₂]₂PbBr₄ stabilizes its monoclinic phase, influencing its luminescence characteristics. The hybrid A-site cations offer exciting prospects for tailoring the chemical composition, structure, and properties of layered perovskites, warranting the novel properties of halide perovskites.

中文翻译：

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杂化阳离子稳定的[(4AMTP)PbBr2]2PbBr4层状钙钛矿的结构和发光的热演化


典型的层状杂化钙钛矿 A ₂ PbBr ₄ 由有机 A 位阳离子和无机 [PbBr ₄ ] ^2– 组成钙钛矿层。或者，这里的 A 位阳离子本身是一种杂化阳离子，即 [(4AMTP)PbBr ₂ ] ₂ ²⁺ ，包含非钙钛矿 PbBr ₂ 型晶格和4AMTP（4-氨基甲基四氢吡喃阳离子）。这种杂化 A 位阳离子如何影响 [(4AMTP)PbBr ₂ ] ₂ PbBr ₄ 2D 层状钙钛矿的结构和发光？在这里，我们通过探索 7–300 K 温度范围内的晶体结构和光致发光 (PL) 来解决这个问题。 [(4AMTP)PbBr ₂ ] ₂ 厘米级单晶PbBr ₄ 在整个温度范围内表现出稳定的单斜晶系P2 ₁ /c空间群，没有表现出任何相变。不存在相变意味着杂化 A 位阳离子带来了更高的结构刚性，这与具有经常表现出相变的有机 A 位阳离子的典型 A ₂ PbBr ₄ 不同在这个温度范围内。 [(4AMTP)PbBr ₂ ] ₂ PbBr ₄ 在室温下的 PL 显示出类似于典型的 A ₂ PbBr < b21> 与有机 A-阳离子，因为杂化和有机 A-位阳离子都不会影响价带和导带边缘。有趣的是，在 70 K 以下，激子发射突然红移 15 meV，从 3.017 eV 变为 3.002 eV，同时寿命增加了一个数量级。单斜晶相层状钙钛矿中类似的温度引起的PL变化先前被归因于自旋禁止的“暗”激子发射，这种发射在较低温度下变得显着。 [(4AMTP)PbBr ₂ ] ₂ PbBr ₄ 中的杂化 A 位阳离子稳定其单斜晶相，影响其发光特性。杂化 A 位阳离子为定制层状钙钛矿的化学组成、结构和性能提供了令人兴奋的前景，保证了卤化物钙钛矿的新颖性能。