Abstract
The electronic structure of a series perovskites ABX3 (A = Cs; B = Ca, Sr, and Ba; X = F, Cl, Br, and I) in the presence and absence of antisite defect XB were systematically investigated based on density-functional-theory calculations. Both cubic and orthorhombic perovskites were considered. It was observed that for certain perovskite compositions and crystal structure, presence of antisite point defect leads to the formation of electronic defect state(s) within the band gap. We showed that both the type of electronic defect states and their individual energy level location within the bandgap can be predicted based on easily available intrinsic properties of the constituent elements, such as the bond-dissociation energy of the B–X and X–X bond, the X–X covalent bond length, and the atomic size of halide (X) as well as structural characteristic such as B–X–B bond angle. Overall, this work provides a science-based generic principle to design the electronic states within the band structure in Cs-based perovskites in presence of point defects such as antisite defect.
Highlights
Crystal Structure on the ElectronicABX3 (A = monovalent organic or inorganic cation, B = bivalent metal, and X = halide) type perovskites have received much attention as candidate materials for various electronic and opto-electronic applications ranging from solar cells to light-emitting diodes [1,2,3].The chemistry and crystal structure of these perovskites determine the band structure needed for the application
We start with the atomic and band structure calculations with cubic CsCaBr3, an experimentally observed perovskite, which serves as a representative of the s-block ABX3 perovskite
The Cs atom had no significant contribution at valance band maxima (VBM) or conduction band minima (CBM), which is commonly observed in both s-block and p-block halide perovskites [27,36]
Summary
In an ionic bond, where the electronegativity difference between metal and halogen is high, the electronic charge cloud is less dispersed along the bond and localized near the nuclei, limiting the overlap between atomic orbitals and resulting in a large bandgap in ionic perovskite. The size of the atom significantly influences the atomic orbital overlap in a bond. Atomic size approximates the energy of the orbitals that are participating in the bonding that leads to the band structure. The effect of atomic size and electronegativity on the electronic structure of halide perovskites can be well understood from the bandgaps of MAPbX3 (X = I, Br, and Cl), a widely studied perovskite system used mainly for photovoltaic applications.
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