The A₂B⁺B′³⁺X₆-type lead-free halide perovskite Cs₂NaInCl₆ has demonstrated limited luminescence performance attributed to parity-forbidden transitions in its intrinsic form. While extensive exploration has been dedicated to partial cation substitution in Cs₂NaInCl₆, there is a noticeable gap in understanding the impact of anion composition on this material. In this study, we investigated the influence of anion composition on the luminescence performance of Cs₂NaInX₆ using first-principles calculations. We first conducted calculations on Cs₂NaInX₆ in its intrinsic state and on Cs₂NaInCl₆ with cation substitution to establish the reliability of the transition dipole moment (TDM) as a luminescence descriptor in this system. Following this, we systematically assessed the formation energies, octahedral distortions, and luminescence properties of Cs₂NaInX₆ with diverse anion compositions. Despite sharing similar stability, closely aligned with the experimentally accessible Cs₂NaInCl₆, all mixed halide structures exhibited significant octahedral distortions. Additionally, most of these structures displayed considerably enhanced TDM compared to their single halide counterparts. Notably, the structures Cs₂NaInX₄X′₂-b and Cs₂NaInX₃X′₃-b demonstrated superior luminescence performance compared to other structures. The absorption spectra calculated for selected structures revealed the enhancement of their photo-absorbance in the presence of iodine, particularly in the low energy region. This observation provides additional evidence that light absorbance in different energy regions can be effectively regulated in this way. Finally, we also investigated other optical properties that impact luminescence performances, such as the energy loss spectrum L(ω), the reflectivity spectrum R(ω) and the refractivity index n(ω). The findings offer insights into optimizing the luminescence performance of lead-free halide perovskites through anion composition variation.

中文翻译：

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通过无铅 Cs2NaInX6（X = Cl、Br 和 I）钙钛矿中阴离子变化调节发光：第一原理研究

A ₂ B ⁺ B' ³⁺ X ₆型无铅卤化物钙钛矿Cs ₂ NaInCl ₆已表现出有限的发光性能，这归因于其固有形式的宇称禁跃跃迁。虽然人们对 Cs ₂ NaInCl ₆中的部分阳离子取代进行了广泛的探索，但在了解阴离子成分对该材料的影响方面存在明显的差距。在本研究中，我们利用第一性原理计算研究了阴离子组成对Cs ₂ NaInX ₆发光性能的影响。我们首先对本征态的Cs ₂ NaInX _{6和阳离子取代的 Cs 2} NaInCl ₆进行计算，以确定过渡偶极矩 (TDM) 作为该系统中发光描述符的可靠性。随后，我们系统地评估了不同阴离子组成的Cs ₂ NaInX _{6的形成能、八面体畸变和发光特性。尽管具有相似的稳定性，与实验上可获得的Cs 2} NaInCl ₆密切相关，但所有混合卤化物结构都表现出显着的八面体扭曲。此外，与单卤化物结构相比，大多数这些结构都表现出显着增强的 TDM。值得注意的是，结构Cs ₂ NaInX ₄ X' ₂ -b和Cs ₂ NaInX ₃ X' ₃ -b与其他结构相比表现出优异的发光性能。对选定结构计算的吸收光谱揭示了它们在碘存在下的光吸收增强，特别是在低能区域。这一观察结果提供了额外的证据，表明不同能量区域的光吸收可以通过这种方式有效调节。最后，我们还研究了影响发光性能的其他光学特性，例如能量损失谱L ( ω )、反射率谱R ( ω ) 和折射率n ( ω )。这些发现为通过阴离子组成变化优化无铅卤化物钙钛矿的发光性能提供了见解。