Effects of Partial Substitution of Bromine on the 
Structural, Electronic, and Optical Properties of CsPbI3 
Insight from First Principles Calculations

Kwalar Barnabas Ngwani; Yerima J. Benson; Ahmad A. D

doi:https://doi.org/10.14445/23497157/IJRES-V12I5P104

Research Article | Open Access | Download PDF

Volume 12 | Issue 5 | Year 2025 | Article Id. IJRES-V12I5P104 | DOI : https://doi.org/10.14445/23497157/IJRES-V12I5P104

Effects of Partial Substitution of Bromine on the Structural, Electronic, and Optical Properties of CsPbI3 Insight from First Principles Calculations

Kwalar Barnabas Ngwani, Yerima J. Benson, Ahmad A. D

Received	Revised	Accepted	Published
10 Aug 2025	28 Sep 2025	14 Oct 2025	30 Oct 2025

Citation :

Kwalar Barnabas Ngwani, Yerima J. Benson, Ahmad A. D, "Effects of Partial Substitution of Bromine on the Structural, Electronic, and Optical Properties of CsPbI3 Insight from First Principles Calculations," International Journal of Recent Engineering Science (IJRES), vol. 12, no. 5, pp. 29-35, 2025. Crossref, https://doi.org/10.14445/23497157/IJRES-V12I5P104

Abstract

Adjusting the composition by partial substitution of halide gives a sure way of improving phase stability and fine tuning the optoelectronic properties of fully inorganic perovskite halides. In this study, first-principles Density Functional Theory (DFT) computations with Spin–Orbit Coupling (SOC) were used to examine the impact of partial bromine integration on the optical, electronic, and structural properties of CsPbI₃. The enhanced CsPbI₂Br structure shows a slight lattice contraction from 6.29 to 6.21 Å, compatible with the smaller ionic radius of bromine, which raises the Goldschmidt tolerance factor from 0.89 to 0.91 and thus stabilizes the cubic phase. The material therefore maintains a direct band gap of 1.68 eV at the R point, positioning it within the maximum range for single-junction solar cells. Projected density-of-states analysis shows that the valence band largely originates from I-5p and Br-4p orbitals hybridized with Pb-6s states, while the conduction band is influenced by Pb-6p orbitals, resulting in strong orbital coupling and low carrier effective masses. Optical analyses show a high static dielectric constant (ε₁(0) = 5.8), very high visible-light absorption (>10⁵ cm⁻¹) and low reflectivity (<0.25), showing exceptional light harvesting potential. An energy-loss peak at 5.1 eV corresponds to bulk plasmon excitation, and the optical conductivity is highest at 3.1 eV, indicating strong inter-band transitions. On the whole, the incorporation of bromine improves the electronic quality, optical response, and structural robustness of CsPbI₃, ranking CsPbI₂Br as a bright and stable material for future generations of perovskite-based photovoltaic and optoelectronic applications.

Keywords

Density functional theory, Lattice contraction, Optoelectronic properties, Phase stability, Structural robustness.

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