Computational Study of Halide Perovskite-Derived A$_2$BX$_6$ Inorganic Compounds: Chemical Trends in Electronic Structure and Structural Stability (1706.08674v1)

Abstract: The electronic structure and energetic stability of A$_2$BX$_6$ halide compounds with the cubic and tetragonal variants of the perovskite-derived K$_2$PtCl$_6$ prototype structure are investigated computationally within the frameworks of density-functional-theory (DFT) and hybrid (HSE06) functionals. The HSE06 calculations are undertaken for seven known A$_2$BX$_6$ compounds with A = K, Rb and Cs, and B = Sn, Pd, Pt, Te, and X = I. Trends in band gaps and energetic stability are identified, which are explored further employing DFT calculations over a larger range of chemistries, characterized by A = K, Rb, Cs, B = Si, Ge, Sn, Pb, Ni, Pd, Pt, Se and Te and X = Cl, Br, I. For the systems investigated in this work, the band gap increases from iodide to bromide to chloride. Further, variations in the A site cation influences the band gap as well as the preferred degree of tetragonal distortion. Smaller A site cations such as K and Rb favor tetragonal structural distortions, resulting in a slightly larger band gap. For variations in the B site in the (Ni, Pd, Pt) group and the (Se, Te) group, the band gap increases with increasing cation size. However, no observed chemical trend with respect to cation size for band gap was found for the (Si, Sn, Ge, Pb) group. The findings in this work provide guidelines for the design of halide A$_2$BX$_6$ compounds for potential photovoltaic applications.

• The paper reveals that band gaps ranging from 0.8 to 2.2 eV vary systematically with A-site and halogen size.
• It employs DFT and HSE06 hybrid functionals to analyze electronic structures and structural distortions in seven A2BX6 compositions.
• The study shows that compositional tuning can optimize band gaps and effective masses, enhancing photovoltaic material performance.

Computational Exploration of A$_2$BX$_6$ Halide Compounds for Photovoltaic Applications

The paper titled "Computational Study of Halide Perovskite-Derived A$_2$BX$_6$ Inorganic Compounds: Chemical Trends in Electronic Structure and Structural Stability" provides a comprehensive theoretical investigation into the electronic and structural properties of A$_2$BX$_6$ inorganic compounds. These compounds, derived from perovskite structures, are analyzed for their potential applications in photovoltaic devices. By utilizing density functional theory (DFT) and hybrid (HSE06) functionals, the research aims to elucidate chemical trends affecting band gaps and structural stability across a range of A, B, and X site compositions.

Methodological Overview

The research employs the HSE06 hybrid functional to computationally assess the band structures and electronic properties of seven specific compositions from the A$_2$BX$_6$ family, with a focus on understanding how variations in chemistry influence electronic properties critical for photovoltaic efficiency. These seven compounds—spanning cations K, Rb, Cs at A sites, and Sn, Pd, Pt, Te at B sites with I as the halogen—serve as benchmarks. The calculations identify trends and provide a basis for expanding the investigation to a broader range of elements using the more computationally efficient GGA-PBE method.

Key Findings and Numerical Results

• Band Gap Trends: HSE06 calculations indicate band gaps spanning 0.8 to 2.2 eV, suitable for photovoltaic applications. For iodide compounds, a recurring theme is that increasing the size of the halide anion (from Cl to Br to I) leads to decreased band gaps. Conversely, increasing the size of A-site cations generally results in increased band gaps within the cubic structures, highlighting the nuanced role of structural constraints on electronic properties.
• Structural Stability: The analysis shows that K and Rb A-site cations promote tetragonal distortions more than Cs, correlating with enhanced band gaps due to changes in octahedral rotations that affect bonding characteristics.
• Effective Mass Analysis: The paper provides a detailed investigation of effective masses, finding heavier hole masses compared to electron masses across all compounds, due to the nature and dispersion of p orbital-derived valence bands.

Implications and Future Directions

These computational insights have significant implications for the design of lead-free solar absorbers. The systematic trends identified suggest strategic pathways for material optimization through compositional tuning. For instance, targeted alloying can adjust band gaps and stabilities, potentially advancing the performance of photovoltaic devices.

The theoretical basis for band gap manipulation posits practical strategies not only for photovoltaic applications but also for broader semiconductor technologies, where control over electronic properties is crucial. Moving forward, experimental validation of these predicted trends could profoundly impact the development of sustainable and environmentally friendly photovoltaic materials.

Conclusion

This work provides a foundational understanding of the chemical and structural factors influencing electronic properties in the A$_2$BX$_6$ family of compounds. By detailing the effects of compositional variations on band gaps and structural stability, the paper offers valuable guidelines for material design in photovoltaic and other semiconductor applications. Such research underscores the importance of computational studies in anticipating material behavior and guiding experimental research towards promising new material compositions.