Short-range Order Parameters in fcc Binary Alloys

Faulkner, John; Pella, S.; Rusanu, Aurelian; Puzyrev, Yevgeniy

doi:10.1007/0-387-25953-8_12

Cited by 2 publications

(2 citation statements)

References 14 publications

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“…This shift occurring between 5 and 10 mol % of GUA doping may be explained by invoking nearest neighbor effects. The probability of each doping GUA being surrounded by only MA cations can be evaluated in a straightforward manner if we assume random substitution (Figure S1), 24 and it drops from about 20% to 0.2% on going from 5 to 10 mol % doping, respectively. This suggests that to accommodate nearest neighbor GUA cations a change in the lattice structure occurs, as sensed by the MA and GUA shifts, owing to the increased probability of there being bulky GUA cations on two neighboring lattice positions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Formation of Stable Mixed Guanidinium–Methylammonium Phases with Exceptionally Long Carrier Lifetimes for High-Efficiency Lead Iodide-Based Perovskite Photovoltaics

et al. 2018

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Methylammonium (MA)- and formamidinium (FA)-based organic-inorganic lead halide perovskites provide outstanding performance as photovoltaic materials, due to their versatility of fabrication and their power conversion efficiencies reaching over 22%. The proposition of guanidinium (GUA)-doped perovskite materials generated considerable interest due to their potential to increase carrier lifetimes and open-circuit voltages as compared to pure MAPbI. However, simple size considerations based on the Goldschmidt tolerance factor suggest that guanidinium is too big to completely replace methylammonium as an A cation in the APbI perovskite lattice, and its effect was thus ascribed to passivation of surface trap states at grain boundaries. As guanidinium was not thought to incorporate into the MAPbI lattice, interest waned since it appeared unlikely that it could be used to modify the intrinsic perovskite properties. Here, using solid-state NMR, we provide for the first time atomic-level evidence that GUA is directly incorporated into the MAPbI and FAPbI lattices, forming pure GUA MAPbI or GUA FAPbI phases, and that it reorients on the picosecond time scale within the perovskite lattice, which explains its superior charge carrier stabilization capacity. Our findings establish a fundamental link between charge carrier lifetimes observed in photovoltaic perovskites and the A cation structure in ABX-type metal halide perovskites.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Formation of Stable Mixed Guanidinium–Methylammonium Phases with Exceptionally Long Carrier Lifetimes for High-Efficiency Lead Iodide-Based Perovskite Photovoltaics

et al. 2018

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“…Warren-Cowley parameters are very often used in binary A 1−x B x alloy research to quantify the degree of SRO, and experimentally the presence of SRO can be measured by x-ray diffraction or scattering technologies. The SRO parameters describe the probability of finding certain types of atoms on the ith coordination shell that surrounds a given reference atom [51].…”

Section: B Free-energy Modelmentioning

confidence: 99%

Density functional theory description of random Cu-Au alloys

et al. 2019

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Density functional alloy theory is used to accurately describe the three core effects controlling the thermodynamics of random Cu-Au alloys. These three core effects are exchange correlation (XC), local lattice relaxations (LLRs), and short-range order (SRO). Within the real-space grid-based projector augmented-wave (GPAW) method based on density functional theory (DFT), we adopt the quasinonuniform XC approximation (QNA), and take into account the LLR and the SRO effects. Our approach allows us to study the importance of all three core effects in a unified way within one DFT code. The results demonstrate the importance of the LLR term and show that going from the classical gradient level approximations to QNA leads to accurate formation energies at various degrees of ordering. The order-disorder transition temperatures for the 25%, 50%, and 75% alloys reach quantitative agreement with the experimental values only when also the SRO effects are considered.

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Short-range Order Parameters in fcc Binary Alloys

Cited by 2 publications

References 14 publications

Formation of Stable Mixed Guanidinium–Methylammonium Phases with Exceptionally Long Carrier Lifetimes for High-Efficiency Lead Iodide-Based Perovskite Photovoltaics

Formation of Stable Mixed Guanidinium–Methylammonium Phases with Exceptionally Long Carrier Lifetimes for High-Efficiency Lead Iodide-Based Perovskite Photovoltaics

Density functional theory description of random Cu-Au alloys

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