Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada.
J Am Chem Soc. 2020 Jun 17;142(24):10780-10793. doi: 10.1021/jacs.0c02198. Epub 2020 Jun 4.
Efficient white-light-emitting single-material sources are ideal for sustainable lighting applications. Though layered hybrid lead-halide perovskite materials have demonstrated attractive broad-band white-light emission properties, they pose a serious long-term environmental and health risk as they contain lead (Pb) and are readily soluble in water. Recently, lead-free halide double perovskite (HDP) materials with a generic formula A(I)B'(III)B″(I)X (where A and B are cations and X is a halide ion) have demonstrated white-light emission with improved photoluminescence quantum yields (PLQYs). Here, we present a series of Bi/In mixed-cationic CsBiInAgCl HDP solid solutions that span the indirect to direct band-gap modification which exhibit tailorable optical properties. Density functional theory (DFT) calculations indicate an indirect-direct band-gap crossover composition when > 0.50. These HDP materials emit over the entire visible light spectrum, centered at 600 ± 30 nm with full-width at half maxima of ca. 200 nm upon ultraviolet light excitation and a maximum PLQY of 34 ± 4% for CsBiInAgCl. Short-range structural insight for these materials is crucial to unravel the unique atomic-level structural properties which are difficult to distinguish by diffraction-based techniques. Hence, we demonstrate the advantage of using solid-state nuclear magnetic resonance (NMR) spectroscopy to deconvolute the local structural environments of these mixed-cationic HDPs. Using ultrahigh-field (21.14 T) NMR spectroscopy of quadrupolar nuclei (In, Cs, and Bi), we show that there is a high degree of atomic-level B'(III)/B″(I) site ordering (i.e., no evidence of antisite defects). Furthermore, a combination of XRD, NMR, and DFT calculations was used to unravel the complete atomic-level random Bi/In cationic mixing in CsBiInAgCl HDPs. Briefly, this work provides an advance in understanding the photophysical properties that correlate long- to short-range structural elucidation of these newly developed solid-state white-light emitting HDP materials.
高效的白光单材料光源是可持续照明应用的理想选择。尽管层状混合卤化铅钙钛矿材料已经表现出了吸引人的宽带白光发射特性，但由于它们含有铅（Pb）并且容易溶于水，因此存在严重的长期环境和健康风险。最近，具有通用公式 A(I)B'(III)B″(I)X（其中 A 和 B 是阳离子，X 是卤化物离子）的无铅卤化物双钙钛矿（HDP）材料已经表现出了改进的光致发光量子产率（PLQY）的白光发射。在这里，我们提出了一系列 Bi/In 混合阳离子 CsBiInAgCl HDP 固溶体，它们跨越了从间接到直接能带隙的修饰，表现出可调节的光学性质。密度泛函理论（DFT）计算表明，当 > 0.50 时，存在间接-直接能带隙交叉组成。这些 HDP 材料在整个可见光光谱中发射，在紫外光激发下，中心位于 600 ± 30nm，半峰全宽约为 200nm，最大 PLQY 为 34 ± 4%，对于 CsBiInAgCl。这些材料的短程结构洞察力对于揭示难以通过基于衍射的技术区分的独特原子级结构特性至关重要。因此，我们展示了使用固态核磁共振（NMR）光谱来分解这些混合阳离子 HDP 的局部结构环境的优势。我们使用四极核（In、Cs 和 Bi）的超高场（21.14 T）NMR 光谱表明，存在高度的原子级 B'(III)/B″(I)位有序（即，没有反位缺陷的证据）。此外，结合 XRD、NMR 和 DFT 计算，我们揭示了 CsBiInAgCl HDP 中完整的原子级随机 Bi/In 阳离子混合。简而言之，这项工作提供了对这些新开发的固态白光发射 HDP 材料的光物理性质的理解，这些性质与长程到短程结构阐明相关。
