All-inorganic cesium lead iodide (CsPbI₃) perovskite has improved thermal stability over the organic–inorganic hybrid perovskites and a suitable bandgap for optoelectronic and photovoltaic applications, but it is thermodynamically unstable at room temperature and has multiple structural polymorphs. Here, we show that the use of long-chain ammonium additives during thin film deposition as surface capping ligands results in the stabilization of metastable bulk CsPbI₃ perovskite phases without alloying mixed cations or anions into the perovskite lattice. Moreover, two different metastable CsPbI₃ perovskite polymorphs in the cubic (α-CsPbI₃) and the much less common orthorhombic (β-CsPbI₃) structures can be directly synthesized in a one-step spin coating film deposition by using oleylammonium or phenylethylammonium additives, respectively, and both phases are stable at room temperature for months. Time-resolved photoluminescence and photoluminescence quenching experiments show that the photoexcited species in the stabilized orthorhombic CsPbI₃ thin film are mainly free carriers under solar illumination with a carrier lifetime of ∼50 ns and carrier diffusion length on the order of ∼100 nm, which implies efficient carrier transport within the film despite the presence of surface ligands. Our results provide a new chemical strategy to synthesize metastable all-inorganic CsPbI₃ perovskites, which, together with the good photophysical properties, will open them up for applications in photovoltaic and other optoelectronic devices.

中文翻译：

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薄膜中CsPbI ₃亚稳钙钛矿多晶型的选择性稳定和光物理性质

与无机-无机杂化钙钛矿相比，全无机碘化铯碘化铅（CsPbI ₃）具有更好的热稳定性，并且适用于光电和光伏应用，并且在室温下热力学不稳定，并且具有多种结构多晶型物。在这里，我们表明在薄膜沉积过程中使用长链铵添加剂作为表面封端配体可稳定亚稳态整体CsPbI ₃钙钛矿相，而不会将混合的阳离子或阴离子合金化到钙钛矿晶格中。此外，两个不同的亚稳CsPbI ₃在立方（α-CsPbI钙钛矿多晶型物₃）和更常见的斜方晶（β-CsPbI ₃）结构可以分别通过使用来o酸铵或苯基乙基铵添加剂在一步旋涂膜沉积中直接合成，并且两相在室温下稳定数月。时间分辨的光致发光和光致发光猝灭实验表明，稳定的正交晶体CsPbI ₃薄膜中的光激发物质主要是自由载流子，在太阳照射下的载流子寿命约为50 ns，载流子扩散长度约为100 nm，这表明尽管存在表面配体，但在膜内仍能有效地运输载体。我们的结果为合成亚稳态全无机CsPbI ₃提供了新的化学策略。 钙钛矿，再加上良好的光物理性质，将使其在光伏和其他光电设备中的应用成为可能。