Lead-free perovskites are among compounds that are currently most investigated for their potential application in photovoltaic due to their non-toxic effect on the environment. In this paper, we are studying the hybrid organic–inorganic lead-free perovskite FASiI3. The material has been examined using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT). These approaches are implemented in the Quantum Espresso code. In fact, we report the structural and electronic properties of this silicon-based perovskite employing GGA-PBE, GGA-PBESol and LDA approximations. The band structure, the total and partial density of states (DOS and PDOS) of FASiI3 has been presented and discussed, it is demonstrated that this perovskite behaves as a semiconductor with direct bandgap. In addition, we have inspected the spin–orbit coupling impact on the bandgap energy, it is demonstrated that the energy gap reduced with SOC, In fact, we discovered bandgap of 1.33 eV applying the GGA-PBESol approach without SOC. The bandgap energy is found to drop to achieve the value 1.10 eV when the SOC correction is added. Moreover, the optical properties were determined and presented. Our results can pave the way to design new efficient and eco-friendly lead-free perovskite solar material for photovoltaic application.

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中文翻译：

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用于光伏应用的新型窄带隙硅基钙钛矿 FASiI3：结构、电子和光学特性的第一原理研究

无铅钙钛矿是目前研究最多的化合物之一，因为它们对环境无毒，因此在光伏领域的潜在应用。在本文中，我们正在研究有机-无机杂化无铅钙钛矿 FASiI3。该材料已使用密度泛函理论 (DFT) 和瞬态密度泛函理论 (TDDFT) 进行了检验。这些方法在 Quantum Espresso 代码中实现。事实上，我们采用 GGA-PBE、GGA-PBESol 和 LDA 近似法报告了这种硅基钙钛矿的结构和电子特性。FASiI3 的能带结构、总态密度和部分态密度（DOS 和 PDOS）已经被提出和讨论，证明了这种钙钛矿表现为具有直接带隙的半导体。此外，我们还检查了自旋轨道耦合对带隙能量的影响，证明了能隙随着 SOC 的增加而减小。事实上，我们在没有 SOC 的情况下应用 GGA-PBESol 方法发现了 1.33 eV 的带隙。当添加 SOC 校正时，发现带隙能量下降至 1.10 eV。此外，还确定并呈现了光学特性。我们的研究结果可以为设计用于光伏应用的新型高效且环保的无铅钙钛矿太阳能材料铺平道路。

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