Imperfections are not 0 K: free energy of point defects in crystals

Mosquera‐Lois, Irea; Kavanagh, Seán R.; Klarbring, Johan; Tolborg, Kasper; Walsh, Aron

doi:10.1039/d3cs00432e

Cited by 14 publications

(10 citation statements)

References 170 publications

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“…To further illustrate the interaction between the defects and H 2 O, we calculated the formation energies of V Cs , V Pb , and V I in α-CsPbI 3 with and without H 2 O insertion, as shown in Figure 7 . The formation energy is calculated with the following equation [ 39 , 41 , 42 , 43 , 44 , 45 ]:

where E ( q ) represents the energy of the defect system in charged state q , E (pristine) represents the energy of the pristine system, ε VBM represents the energy of the valence band maximum (VBM), and E F represents the Fermi energy in reference to ε VBM . n i represents the number of atoms i added ( n i < 0) or removed ( n i > 0) from the system, E ( i ) represents the energy of the element solid i , and μ i represents the chemical potential in reference to E ( i ).…”

Section: Resultsmentioning

confidence: 99%

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First-Principles Investigation into the Interaction of H2O with α-CsPbI3 and the Intrinsic Defects within It

Wang,

2024

Materials

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CsPbI3 possesses three photoactive black phases (α, β, and γ) with perovskite structures and a non-photoactive yellow phase (δ) without a perovskite structure. Among these, α-CsPbI3 exhibits the best performance. However, it only exists at high temperatures and it tends to transform into the δ phase at room temperature, especially in humid environments. Therefore, the phase stability of CsPbI3, especially in humid environments, is the main obstacle to its further development. In this study, we studied the interaction of H2O with α-CsPbI3 and the intrinsic defects within it. It was found that the adsorption energy in the bulk is higher than that on the surface (−1.26 eV in the bulk in comparison with −0.60 eV on the surface); thus, H2O is expected to have a tendency to diffuse into the bulk once it adsorbs on the surface. Moreover, the intrinsic vacancy of VPb0 in the bulk phase can greatly promote H2O insertion due to the rearrangement of two I atoms in the two PbI6 octahedrons nearest to VPb0 and the resultant breaking of the Pb–I bond, which could promote the phase transition of α-CsPbI3 in a humid environment. Moreover, H2O adsorption onto VI+1 contributes to a further distortion in the vicinity of VI+1, which is expected to enhance the effect of VI+1 on the phase transition of α-CsPbI3. Clarifying the interaction of H2O with α-CsPbI3 and the intrinsic defects within it may provide guidance for further improvements in the stability of α-CsPbI3, especially in humid environments.

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Section: Resultsmentioning

confidence: 99%

“…To further illustrate the interaction between the defects and H2O, we calculated the formation energies of VCs, VPb, and VI in α-CsPbI3 with and without H2O insertion, as shown in Figure 7. The formation energy is calculated with the following equation [39,[41][42][43][44][45]:…”

Section: Near Vpbmentioning

confidence: 99%

First-Principles Investigation into the Interaction of H2O with α-CsPbI3 and the Intrinsic Defects within It

Wang,

2024

Materials

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“…Also for these systems, several relaxations of similar structures are performed with DFT, and vibrational free energies have been shown to be important for quantitative properties in several cases. 43,44 ■ COMPUTATIONAL METHODS First-Principles Calculations. Total energy calculations are performed using DFT as implemented within the Vienna ab initio simulation package (VASP).…”

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confidence: 99%

“…Finally, a similar methodology of training a force field on relaxation trajectories to calculate vibrational free energies could potentially be used when modeling defects, surfaces, and interfaces in crystals. Also for these systems, several relaxations of similar structures are performed with DFT, and vibrational free energies have been shown to be important for quantitative properties in several cases. , …”

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Low-Cost Vibrational Free Energies in Solid Solutions with Machine Learning Force Fields

Tolborg,

Walsh

2023

J. Phys. Chem. Lett.

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The rational design of alloys and solid solutions relies on accurate computational predictions of phase diagrams. The cluster expansion method has proven to be a valuable tool for studying disordered crystals. However, the effects of vibrational entropy are commonly neglected due to the computational cost. Here, we devise a method for including the vibrational free energy in cluster expansions with a low computational cost by fitting a machine learning force field (MLFF) to the relaxation trajectories available from cluster expansion construction. We demonstrate our method for two (pseudo)binary systems, Na 1– x K x Cl and Ag 1– x Pd x , for which accurate phonon dispersions and vibrational free energies are derived from the MLFF. For both systems, the inclusion of vibrational effects results in significantly better agreement with miscibility gaps in experimental phase diagrams. This methodology can allow routine inclusion of vibrational effects in calculated phase diagrams and thus more accurate predictions of properties and stability for mixtures of materials.

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Doping engineering in the CdTe thin film solar cells

Duan,

Wang,

Yan

2024

cMat

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Cadmium telluride (CdTe) thin film solar cells have gained significant attention in the photovoltaic industry due to their high efficiency and low cost. CdTe solar cells have achieved a high‐power conversion efficiency of 23.1%. To further boost the device's performance, it is crucial to systematically tune the doping concentration and carrier concentration, which are dominated by the doping approach and the following dopant activation processes. Both Group I elements (e.g., Cu) and Group V elements (e.g., As) doping have demonstrated high efficiency and utilizing various doping techniques. This review provides an overview of the history of the CdTe thin film technology, doping mechanisms, doping techniques, challenges, and potential solutions to further improve device performance.

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Imperfections are not 0 K: free energy of point defects in crystals

Abstract: Temperature plays an important role in the formation of point defects. We review different contributions to defect free energies and how to model them, outlining strategies to reduce the associated computational burden.

Cited by 14 publications

References 170 publications

First-Principles Investigation into the Interaction of H2O with α-CsPbI3 and the Intrinsic Defects within It

First-Principles Investigation into the Interaction of H2O with α-CsPbI3 and the Intrinsic Defects within It

Low-Cost Vibrational Free Energies in Solid Solutions with Machine Learning Force Fields

Doping engineering in the CdTe thin film solar cells

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