First-principles Study On The Electronic And Optical Properties Of Cubic ABX3 Halide Perovskites (1309.0070v1)

Abstract: The electronic properties of ABX3 (A = Cs, CH3NH3, NH2CHNH2; B = Sn, Pb; X = Cl, Br, I) type compounds in the cubic phase are systematically studied using the first-principles calculations. We find that these compounds have direct band gaps at R point where the valance band maximum is an anti-bonding state of B s-X p coupling, while the conduction band minimum is a non-bonding state with B p characters. The chemical trend of their properties as A or B or X varies is fully investigated, which is of great importance to understand and optimize this kind of solar cell materials. We find that: (i) as the size of A increases, the band gap of ABX3 will increase; (ii) as B varies from Sn to Pb, the band gap of ABX3 will increase; and (iii) as X ranges from Cl to Br to I, the band gap will decrease. We explained these trends by analyzing their band structures. Furthermore, optical properties of the ABX3 compounds are investigated. Our calculations show that taking into account the spin-orbit coupling effect is crucial for predicting the accurate band gap of these halide perovskites. We predict that CH3NH3SnBr3 is a promising material for solar cells absorber with a perfect band gap and good optical absorption.

• The paper demonstrates how varying A, B, and X components tunes the band gap of cubic ABX3 perovskites using first-principles DFT.
• It quantifies the impact of spin-orbit coupling on band gap reduction, showing decreases of ~0.35 eV for Sn-based and ~1.13 eV for Pb-based compounds.
• The study identifies CH3NH3SnBr3 and NH3CHNH3SnBr3 as promising solar absorber candidates with optimal band gaps and enhanced nontoxicity.

Electronic and Optical Properties of Cubic Halide Perovskites through First-Principles Calculations

This paper presents a comprehensive first-principles computational paper on ABX₃ halide perovskites, where A can be Cs, CH₃NH₃, or NH₃CHNH₃; B is Sn or Pb, and X is Cl, Br, or I. The authors systematically investigate the electronic and optical properties of these compounds in their cubic phases, leveraging the Vienna ab initio simulation package (VASP) within the framework of density functional theory (DFT).

The research focuses primarily on the electronic band structure and the influence of various components on the band gap. Significant chemical trends were elucidated: as the size of A increases, or as B changes from Sn to Pb, the band gap increases. Conversely, as X transitions from Cl to Br to I, the band gap decreases. These findings are attributed to shifts in the chemical bonding and the resulting band hybridizations as indicated by the analysis of band structures and density of states (DOS).

The paper highlights the importance of including spin-orbit coupling (SOC) in calculations involving these compounds, particularly those with heavier elements such as Sn and Pb. The SOC significantly impacts the conduction band minimum (CBM), splitting it into 1/2 and 3/2 manifolds, thus affecting the overall band gaps. The band gap decrease due to SOC is approximately 0.35 eV for Sn-based and 1.13 eV for Pb-based compounds, underscoring SOC's criticality for accurate predictions of electronic properties.

Two compounds, CH₃NH₃SnBr₃ and NH₃CHNH₃SnBr₃, emerged as promising candidates for solar cell absorbers. Their band gaps fall within the ideal range (1.1 eV to 1.5 eV) for high-efficiency solar cells, and they also exhibit favorable optical absorption characteristics. Additionally, these materials offer nontoxicity advantages over lead-based perovskites.

The theoretical implications of this paper lie in the detailed elucidation of how different elemental substitutions and structural variations can tailor the electronic properties of halide perovskites. Practically, this provides a pathway to engineer and optimize new materials for solar energy applications through band structure engineering, potentially including alloying strategies to tune properties further.

Future directions suggested by this work could involve experimental validation of the predicted optical properties and band structures, especially for the more promising CH₃NH₃SnBr₃ and NH₃CHNH₃SnBr₃ compounds. Moreover, additional computational investigations might extend this work to other phases and dimensionalities of perovskites, further broadening the scope of material optimization for photovoltaic applications. The robustness of first-principles methods in providing accurate property predictions, especially with SOC inclusion, will continue to be instrumental in the development of novel optoelectronic materials.