Due to the outstanding power conversion efficiency (PCE), lightweight, flexible, and low manufacturing cost, perovskite solar cells (PSCs) attract a lot of attention as the most promising candidate for the next generation of solar cells. However, the issue of poor intrinsic stability of the absorber materials and operational stability of devices remains unsolved. In this study, first-principle calculations were performed on the CsPbX₃ (X = Br or I) perovskites to provide insight into the structural, mechanical, vibrational and electronic properties of CsPbBr₃ and CsPbI₃ for their applications as active layers of solar cells. It was found that the calculated lattice parameters are in good agreement with the experimental results. CsPbBr₃ and CsPbI₃ have negative energy of formation, which implies that the materials are thermodynamically stable. The calculated band structures indicate that CsPbBr₃ and CsPbI₃ are semiconductors with direct bandgaps along R-symmetry point. Furthermore, cluster expansion and simulations of Monte-Carlo were performed to identify new possible CsPbBr_1-xI_x structures and evaluate the effect of temperature on the system. The ground-state search generated 26 new multi-component CsPbBr_1-xI_x structures, and the temperature-profile showed that the system mixes well at ∼800 K. Thus, the phase stability insight is crucial for the development of these promising perovskite solar cells.

Cationic doping has been recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn ³⁺ ) ions that undergo a disproportionation reaction in lithium manganese oxide-based (LiMn ₂ O ₄ ) lithium-ion batteries. However, the effect of surface doping on the major LiMn ₂ O ₄ surfaces and their interactions with the electrolyte components is not yet fully understood. In this work, spin-polarised density functional theory-based calculations [DFT + U -D3 (BJ)] were employed to study the adsorption of the electrolyte components ethylene carbonate (EC) and hydrogen fluoride (HF) onto the Nb-doped major LiMn ₂ O ₄ (001), (011), and (111) surfaces. During the substitution of niobium for manganese ions in the second surface layers (Nb _second ), it was found that the (111) surface stability improves, resulting in an enhanced (111) plane on the morphology. However, replacing the first (Nb _first ) as well as both top and sub-surface (Nb _both ) layers of Mn atoms in the slabs maintains the same stability trend as in the pure pristine surfaces. Moreover, both adsorbates greatly preferred binding to the surfaces through the Nb instead of Mn atoms, and the largest adsorption energy was calculated for EC on the LiMn ₂ O ₄ (011) surface doped on the Nb _second site and for HF on the LiMn ₂ O ₄ (111) surface doped on the Nb _both site. Furthermore, the EC/HF adsorptions further enhance the stability of the Nb _second (111) surface plane. However, minimal charge transfer was calculated for both HF and EC interacting with the pure and Nb-doped surfaces. Our findings are interesting, since exposing the (111) surface promotes the formation of a stable solid electrolyte interface (SEI), significantly reducing Mn dissolution and enhancing the adsorption of EC and HF.

The study explores the Ni-rich transition metal as a dopant on the Mn (16d) site of the LiMn_1-xNi_xO₄ cathode material. However, lithium manganese oxide is hindered by a limited cycle life, caused by the dissolution of manganese into the electrolyte during electrochemical cycling. Doping lithium-ion battery materials with TM generally enhances their ability to maintain electrochemical capacity over many cycles without compromising the initial reversible capacity at room temperature. This study utilised the genetic algorithm approach and first-principles calculations to investigate the LiMn2O4 spinel structure. This method identified the most stable phases by simplifying atomic interactions in the LiMn₂O₄-LiNi₂O₄ system using a series of clusters, which facilitated the corresponding thermodynamic analysis. The comparison and exploration between the full optimized and volume optimized binary calculation was to observe the % difference of the two binary diagrams yielding 13 meV and 1.1 meV, respectively. The two binary ground state diagrams depict the miscibility constituent’s behaviour, producing new phases (62 and 77) with different coordinates. The study revealed the five most stable phases at the ground state line, one of which is the opposite (LiMn_0.5Ni_1.5O₄) at X = 0.75 of the high-potential cathode material LiMn_0.5Ni_1.5O₄.

First-principles calculations based on density functional theory (DFT) are a powerful tool in data-oriented materials research. The choice of approximation for the exchange-correlation functional is crucial, as it strongly affects the accuracy of DFT calculations. This study compares the performance capabilities of three approximations on the energetics, mechanical and electronic properties, and crystal structure of NaAlP₂O₇, which is an insulator with a wide band gap that suppresses its electronic conductivity. Two of these approximations are based on Perdew–Burke–Ernzerhof (PBE) generalized gradient approximation (GGA) and the other on the strongly constrained and appropriately normed (SCAN) meta-GGA. We explore these materials as a contribution to the development of new solid electrolytes (SEs) for sodium-ion batteries (NIBs), which have the potential to mitigate challenges related to lifecycle, safety, and low ionic conductivity. The performance of these batteries largely emanates from the extraordinary demand for high-performing energy storage technologies. This study revealed that PBEsol accurately predicted lattice parameters that closely aligned with experimental values. However, r2SCAN provided the most reliable predictions of the structural and electronic properties of the NaAlP₂O₇ solid electrolyte compared to PBE and PBEsol. Findings demonstrated that the material is structurally, mechanically, electronically, and thermodynamically stable, but exhibits vibrational instability, which may scatter ions and reduce ionic conductivity due to the presence of imaginary frequencies. Our results highlight the importance of selecting appropriate functionals for solid electrolyte DFT computations. The r2SCAN functional appears to be a promising choice for calculating NaAlP₂O₇ properties.

Using first-principles calculations and cluster expansion, this study generates new possible stable phases of t-LLZO containing a supervalent cation, Ta, on the Zr-site as a way to enhance the conductivity of the tetragonal crystal structure. The Monte-Carlo simulation was then used to provide further insight into the behaviour of the Ta-doped phases as a function of temperature under the canonical ensemble. The cluster expansion binary ground-state diagram generated 28 new multi-component Li₅La₃Zr_2-xTa_xO₁₂ structures that are miscible. It is found that all the structures are thermodynamically stable with negative enthalpy of formation. The Monte-Carlo temperature profile shows no phase separation, and the system mixes well at ~900K. Further density functional theory calculations were performed on the most stable generated Ta-doped LLZO structures to determine the structural properties of the structures for their application as active solid-state electrolytes. It is found that the generated structures exhibit good structural stability due to the smooth decrease in calculated lattice parameters, which indicates that the smaller the difference between the dopant ionic radius and the critical dopant radius, the higher the conductivity. Therefore, the findings provide a better understanding of the phase stability of the generated Ta-doped LLZO structures, which paves the way for further analysis of the rate of lithium-ion diffusion and the mobility of the lanthanum, zirconium, tantalum, and oxygen ions in the systems at high temperatures.