Halide Segregation in Mixed-Halide Perovskites: Influence of A-Site Cations

Knight, Alexander J.; Borchert, Juliane; Oliver, Robert D. J.; Patel, Jay B.; Radaelli, P. G.; Snaith, Henry J.; Johnston, Michael B.; Herz, Laura M.

doi:10.1021/acsenergylett.0c02475

Cited by 174 publications

(221 citation statements)

References 63 publications

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“…The film was then exposed to the segregation-driving CW illumination and the measurements were repeated after stabilisation of the PL spectral changes, resulting in μ = 37.2 ± 0.6 cm 2 /(Vs) . Such similar μ values of charge carriers immediately after photoexcitation are consistent with halide segregation occurring only in a small portion of the film despite drastic changes in PL lineshape 2 , 9 , 17 , which results in the minimal impact of halide demixing on the charge transport properties of the majority phase. This finding agrees with our recent observations in a parallel study carried out on identical films, in which XRD diffraction showed good preservation of material crystallinity upon halide segregation 17 .…”

Section: Resultssupporting

confidence: 69%

“…Such similar μ values of charge carriers immediately after photoexcitation are consistent with halide segregation occurring only in a small portion of the film despite drastic changes in PL lineshape 2 , 9 , 17 , which results in the minimal impact of halide demixing on the charge transport properties of the majority phase. This finding agrees with our recent observations in a parallel study carried out on identical films, in which XRD diffraction showed good preservation of material crystallinity upon halide segregation 17 . To understand the impact of heterogeneities on the transport properties, we tuned the OPTP photoexcitation wavelength to 720 nm.…”

Section: Resultssupporting

confidence: 69%

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Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

et al. 2021

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Mixed halide perovskites can provide optimal bandgaps for tandem solar cells which are key to improved cost-efficiencies, but can still suffer from detrimental illumination-induced phase segregation. Here we employ optical-pump terahertz-probe spectroscopy to investigate the impact of halide segregation on the charge-carrier dynamics and transport properties of mixed halide perovskite films. We reveal that, surprisingly, halide segregation results in negligible impact to the THz charge-carrier mobilities, and that charge carriers within the I-rich phase are not strongly localised. We further demonstrate enhanced lattice anharmonicity in the segregated I-rich domains, which is likely to support ionic migration. These phonon anharmonicity effects also serve as evidence of a remarkably fast, picosecond charge funnelling into the narrow-bandgap I-rich domains. Our analysis demonstrates how minimal structural transformations during phase segregation have a dramatic effect on the charge-carrier dynamics as a result of charge funnelling. We suggest that because such enhanced recombination is radiative, performance losses may be mitigated by deployment of careful light management strategies in solar cells.

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Section: Resultssupporting

confidence: 69%

Section: Resultssupporting

confidence: 69%

Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

et al. 2021

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“…Although the resulting increased bandgaps lower the optical absorption, the stability of bromide-based perovskites is significantly enhanced [56] and this is confirmed by thermal decomposition of MAPbX 3 perovskites [57]. Furthermore, the stability seems to be also linked to the A-site cation mixture as observed in the case of halide segregation [58]. Using binary mixtures of the aforementioned seven A-site cations and three halogens we assemble the perovskite structures of formula A x A' 1−x PbX y X' z X" 3−y−z .…”

Section: Mixed-cation Mixed-halide Perovskitesmentioning

confidence: 78%

Investigation of Opto-Electronic Properties and Stability of Mixed-Cation Mixed-Halide Perovskite Materials with Machine-Learning Implementation

et al. 2021

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The feasibility of mixed-cation mixed-halogen perovskites of formula AxA’1−xPbXyX’zX”3−y−z is analyzed from the perspective of structural stability, opto-electronic properties and possible degradation mechanisms. Using density functional theory (DFT) calculations aided by machine-learning (ML) methods, the structurally stable compositions are further evaluated for the highest absorption and optimal stability. Here, the role of the halogen mixtures is demonstrated in tuning the contrasting trends of optical absorption and stability. Similarly, binary organic cation mixtures are found to significantly influence the degradation, while they have a lesser, but still visible effect on the opto-electronic properties. The combined framework of high-throughput calculations and ML techniques such as the linear regression methods, random forests and artificial neural networks offers the necessary grounds for an efficient exploration of multi-dimensional compositional spaces.

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“…Moreover, in such a sequence of reducing dimensionality, we would expect diffraction of larger RDPs to be weaker, since there would initially be few instances of adjacent and periodic high-n RDPs, but once they split into lower-n RDPs, these structures would be immediately adjacent to each other, thus promoting diffraction 21 . Considering the small percentage of bromine in the (MAPbBr 3 ) 0.05 (FAPbI 3 ) 0.95 films, we posit that the difference in the 2D/3D transformation pathways arises due to the greater stability of FAPbI 3 compared to MAPbI 3 , where the latter is known to exhibit poorer thermal stability due to loss of volatile species under thermal stress and is more easily converted to PbI 2 26,27 .…”

Section: Dmentioning

confidence: 97%

Multication perovskite 2D/3D interfaces form via progressive dimensional reduction

et al. 2021

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Many of the best-performing perovskite photovoltaic devices make use of 2D/3D interfaces, which improve efficiency and stability – but it remains unclear how the conversion of 3D-to-2D perovskite occurs and how these interfaces are assembled. Here, we use in situ Grazing-Incidence Wide-Angle X-Ray Scattering to resolve 2D/3D interface formation during spin-coating. We observe progressive dimensional reduction from 3D to n = 3 → 2 → 1 when we expose (MAPbBr3)0.05(FAPbI3)0.95 perovskites to vinylbenzylammonium ligand cations. Density functional theory simulations suggest ligands incorporate sequentially into the 3D lattice, driven by phenyl ring stacking, progressively bisecting the 3D perovskite into lower-dimensional fragments to form stable interfaces. Slowing the 2D/3D transformation with higher concentrations of antisolvent yields thinner 2D layers formed conformally onto 3D grains, improving carrier extraction and device efficiency (20% 3D-only, 22% 2D/3D). Controlling this progressive dimensional reduction has potential to further improve the performance of 2D/3D perovskite photovoltaics.

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Halide Segregation in Mixed-Halide Perovskites: Influence of A-Site Cations

Cited by 174 publications

References 63 publications

Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

Phase segregation in mixed-halide perovskites affects charge-carrier dynamics while preserving mobility

Investigation of Opto-Electronic Properties and Stability of Mixed-Cation Mixed-Halide Perovskite Materials with Machine-Learning Implementation

Multication perovskite 2D/3D interfaces form via progressive dimensional reduction

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