Impact of metastable defect structures on carrier recombination in solar cells

Kavanagh, Seán R.; Scanlon, David O.; Walsh, Aron; Freysoldt, Christoph

doi:10.1039/d2fd00043a

“…This configuration reduces cation-cation repulsion and lattice strain, facilitated by highly mobile Li + which can easily migrate from T d to O h sites. 111 Finally, the exchange type reaction Ni i → Li i + Ni Li is found to spontaneously occur, again reflecting the high mobility of Li + . 82 All O i relaxed into dumbbell configurations with O-O distance within 1.4 Å.…”

Section: Interstitialsmentioning

confidence: 89%

Intrinsic Defect Chemistry of High-Voltage LiMn1.5Ni0.5O4 (LMNO) Spinel Cathode

Cen

¹

,

Zhu

²

,

Kavanagh

³

et al. 2023

Preprint

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High-voltage spinel LiMn1.5Ni0.5O4 (LMNO) can exist in a Mn/Ni ordered P4_332 or disordered Fd-3m arrangement with a majority of literature studies reporting improved electrochemical performance for the disordered phase. Through modifying synthesis conditions, the Mn/Ni ordering can be tuned, however oxygen and Mn3+ stoichiometries are also affected, making it difficult to decouple these responses and optimise performance. Here, we investigate all intrinsic defects in P4_332 LMNO under various growth conditions, using density functional theory (DFT) calculations. We find that the majority of defects are deep and associated with small polarons (Mn3+, Mn2+ and Ni3+) formation. The tendency for cation disorder can be explained by the low formation energy of the antisite defects and their stoichiometric complexes. The intrinsic Fermi level of LMNO varies from moderately n-type under oxygen-poor conditions to weakly p-type under oxygen-rich conditions. Our work explains experimental observations (e.g. the Mn/Ni disorder) and provides guidelines for defect-controlled synthesis.

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“…Similar to the structural features observed in Li i , Li-Ni and Mn-Li split-interstitial configurations are also seen for Ni i and Mn i . This configuration reduces cation-cation repulsion and lattice strain, facilitated by highly mobile Li + which can easily migrate from T d to O h sites 111. Finally, the exchange type reaction Ni i → Li i + Ni Li is found to spontaneously occur, again reflecting the high mobility of Li + 82.…”

mentioning

confidence: 87%

Cation disorder dominates the defect chemistry of high-voltage LiMn1.5Ni0.5O4 (LMNO) spinel cathodes

Cen

¹

,

Zhu

²

,

Kavanagh

³

et al. 2023

Preprint

View full text Add to dashboard Cite

High-voltage spinel LiMn1.5Ni0.5O4 (LMNO) can exist in a Mn/Ni ordered P4_332 or disordered Fd-3m arrangement with a majority of literature studies reporting improved electrochemical performance for the disordered phase. Through modifying synthesis conditions, the Mn/Ni ordering can be tuned, however oxygen and Mn3+ stoichiometries are also affected, making it difficult to decouple these responses and optimise performance. Here, we investigate all intrinsic defects in P4_332 LMNO under various growth conditions, using density functional theory (DFT) calculations. We find that the majority of defects are deep and associated with small polarons (Mn3+, Mn2+ and Ni3+) formation. The tendency for cation disorder can be explained by the low formation energy of the antisite defects and their stoichiometric complexes. The intrinsic Fermi level of LMNO varies from moderately n-type under oxygen-poor conditions to weakly p-type under oxygen-rich conditions. Our work explains experimental observations (e.g. the Mn/Ni disorder) and provides guidelines for defect-controlled synthesis.

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“…in other structure-searching approaches, such as the investigation of symmetry breaking distortions in perovskites 48 or point defects 20,49 . The magnitudes of these randomly-directed atomic displacements d are themselves randomly selected from a normal distribution of chosen standard deviation σ (Eq.…”

Section: Structure Search Strategymentioning

confidence: 99%

“…Moreover, we demonstrate the strong effect on defect formation energies and their charge transition levels, illustrating the importance of exploring the defect configurational space for accurate predictions of defect properties (Impact on defect properties). Additionally, while defect properties are often determined by the ground state structure, there are cases when low energy metastable structures can significantly affect behaviour 10,19,20 . Accordingly, we tested our approach for low-energy metastable configurations by considering the DX centres in GaAs, which have been extensively studied due to their anomalous physical properties and technological importance (Locating metastable structures).…”

Section: Introductionmentioning

confidence: 99%

Identifying the ground state structures of point defects in solids

Mosquera‐Lois

¹

,

Kavanagh

²

,

Walsh

³

et al. 2023

Self Cite

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Point defects are a universal feature of crystals. Their identification is addressed by combining experimental measurements with theoretical models. The standard modelling approach is, however, prone to missing the ground state atomic configurations associated with energy-lowering reconstructions from the idealised crystallographic environment. Missed ground states compromise the accuracy of calculated properties. To address this issue, we report an approach to navigate the defect configurational landscape using targeted bond distortions and rattling. Application of our workflow to eight materials (CdTe, GaAs, Sb2S3, Sb2Se3, CeO2, In2O3, ZnO, anatase-TiO2) reveals symmetry breaking in each host crystal that is not found via conventional local minimisation techniques. The point defect distortions are classified by the associated physico-chemical factors. We demonstrate the impact of these defect distortions on derived properties, including formation energies, concentrations and charge transition levels. Our work presents a step forward for quantitative modelling of imperfect solids.

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Impact of metastable defect structures on carrier recombination in solar cells

Abstract: The efficiency of a solar cell is often limited by electron-hole recombination mediated by defect states within the band gap of the photovoltaic (PV) semiconductor. The Shockley-Read-Hall (SRH) model considers...

Cited by 21 publications

References 53 publications

Intrinsic Defect Chemistry of High-Voltage LiMn1.5Ni0.5O4 (LMNO) Spinel Cathode

Intrinsic Defect Chemistry of High-Voltage LiMn1.5Ni0.5O4 (LMNO) Spinel Cathode

Cation disorder dominates the defect chemistry of high-voltage LiMn1.5Ni0.5O4 (LMNO) spinel cathodes

Identifying the ground state structures of point defects in solids

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