The intrinsic properties of FA(1−x)MAxPbI3 perovskite single crystals

Huang, Yuan; Li, Liang; Liu, Zonghao; Jiao, Haoyang; He, Yuqing; Wang, Xiaoge; Zhu, Rui; Wang, Dong; Sun, Junliang; Chen, Qi; Zhou, Huanping

doi:10.1039/c7ta01441d

Cited by 159 publications

(131 citation statements)

References 41 publications

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“…The orbitals of the countercations do not significantly contribute to the frontier bands, but influence the perovskite lattice type, lattice constants, and structural stability. Other experimental approaches to short-term stabilization of α-FAPbI 3 (besides rapid thermal quenching) include doping of the material with MA, [22][23][24][25] Cs, [26,27] and both MA and Cs, [28][29][30] but not with organic cations that bond stronger to the inorganic skeleton than FA. The higher the degree of covalent conjugation, the lower is the bandgap, the larger are radii of the excitons, the lower are the exciton binding energies, and, finally, the more efficient is the charge carrier transport in the material.…”

Section: Introductionmentioning

confidence: 99%

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX₃ (X = Br, I)

Oranskaia

Schwingenschlögl

2019

Advanced Energy Materials

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10 4 cm −1 in the visible-to-infrared region, bandgaps of 1.4-2.3 eV depending on A and X, form Wannier excitons of hundreds of Å diameter and tens of meV binding energy, and have high charge carrier diffusion lengths of up to µm. [1][2][3][4] The highest certified perovskite solar cell power conversion efficiency rapidly increased from 3.8% in 2009 to 22.1% in 2016 using hybrid FAPbI 3 doped with 5% MAPbBr 3[5] (and now stands at 24.2% [6] ). MA and FA stand for methylammonium and formamidinium, light polar organic cations formed by the simplest protonated amine NH 2 CH 3 and amidine NH 2 CHNH. Being incorporated into the lead halide crystal lattice, these organic cations participate not only in strong electrostatic and van der Waals interactions with the inorganic skeleton but also in hydrogen H···X bonding between H atoms (organic cation) and X atoms (inorganic skeleton) that is absent in all-inorganic perovskites. Being an electrondeficient π-conjugated system, FA also participates in π-anion π···X bonding with X atoms. [7] Though the organic cations do not directly determine the optoelectronic properties of hybrid perovskites, they do stabilize the inorganic skeleton of "3D" α-FAPbX 3 (cubic phase) and determine its defect properties, especially regarding X-defects. Goal of the present study therefore is to investigate the role of the FA bonding properties in α-FAPbX 3 and to propose promising organic cation doping strategies.The rising star of hybrid perovskite field of solar energy harvesting, α-FAPbI 3 , has a narrower bandgap than well-studied β-MAPbI 3 (tetragonal phase) and, more importantly, is more stable against decomposition and degradation. [8][9][10][11][12][13] Despite many advantages, β-MAPbI 3 has the serious problem that it is intrinsically thermodynamically unstable, decomposing into PbI 2 and MAI (and further into volatile amine and HI), and readily degrades even at moderate operating temperatures when exposed to water and/or oxygen. Lower affinity of α-FAPbI 3 to decomposition and degradation is related to weaker acidity (as a result of aromatic stabilization), larger volume, and stronger bonding with the halides of FA than MA, which manifests in experiment as suppressed hysteresis due to I-migrations. [5,14] The mobile I-defects in β-MAPbI 3 are detrimental not only to the structural stability of the material but also to its charge transport properties when acting as electron-hole recombination centers. [15][16][17] In this respect, it is crucial to understand the influence of FA on the X-migrations in α-FAPbX 3 and to identify ways to manipulate them by introducing stronger bonding organic cations as dopants.Chemical bonding of formamidinium (FA) with the inorganic perovskite skeleton of FAPbX 3 (X = Br, I) is studied with emphasis on the differences to methylammonium: stronger hydrogen bonding, the presence of π-anion bonding, and more sterically hindered motion inside the perovskite inorganic cage. Organic cation dopants fitting in the perovskite cubic cell and being capable of hydroge...

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Section: Introductionmentioning

confidence: 99%

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX₃ (X = Br, I)

Oranskaia

Schwingenschlögl

2019

Advanced Energy Materials

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“…23,25 The phase stability of MA 1Àx FA x PbI 3 has been studied for samples stored under a nitrogen atmosphere, indicating that for FA-rich compositions with x > 0.76, partial transition to the hexagonal phase is observed within days, while for compositions with more MA, the hexagonal phase is not observed by X-ray diffraction. 30 The propensity for hybrid perovskites to react with water has also been reported.…”

mentioning

confidence: 99%

“…[22][23][24][25] We have previously shown that for compositions MA 1Àx FA x PbI 3 0 < x < 0.2 the structures are best described by a tetragonal unit cell from X-ray diffraction, while the rest of the composition range, 0.2 # x # 1, forms with a cubic cell, space group Pm 3m.…”

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Understanding the stability of mixed A-cation lead iodide perovskites

et al. 2017

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The routes and kinetics of the degradation of thin films of methylammonium (MA)/formamidinium (FA) lead iodide perovskites (MA 1Àx FA x PbI 3 , 0 # x # 1) under dry atmospheric conditions have been investigated. MA-rich phases decompose to the precursor iodide salts and PbI 2 , while FA-rich phases convert mainly to the yellow hexagonal phase. The reactivity is strongly inhibited for mixed cation phases of MA 1Àx FA x PbI 3 , for x ¼ 0.4 to 0.6, where the decomposition routes available to end member phases become less favourable. It is shown that for pristine films with x ¼ 0.6, PbI 2 formation can be completely suppressed for up to 10 days. Kinetic analysis reveals that the rate of PbI 2 formation decays exponentially with increasing FA content until x ¼ 0.7, beyond which the FA containing perovskite transforms rapidly to the hexagonal phase. Ab initio simulations of the decomposition reaction energies fully support the increased kinetic stability found experimentally for the mixed A-cation perovskites.Hybrid lead halide perovskites have recently risen to prominence as highly versatile materials for optoelectronic technologies, particularly high efficiency, solution processed solar cells.1-4 They display near optimal band gap for solar light absorption, high absorption coefficients, steep absorption onsets and signicant charge carrier lifetimes (and thus diffusion lengths).2,5 These properties, combined with the processability of these materials, 6,7 have resulted in solar cell device efficiencies rising rapidly to over 22%.8 However, the commercial applicability of these materials is hampered by their relative lack of stability compared to established inorganic and organic semiconductors.9-11 By chemical site-substitution at any of the A, B or X sites of the ABX 3 perovskite structure, it has been found that it is possible to tune the properties and, most pertinently, the stability of the resultant material. 12-14The archetypal hybrid perovskite methylammonium (MA) lead iodide (CH 3 NH 3 PbI 3 ), MAPI, crystallises in the tetragonal space group I4/mcm at room temperature.15 Formamidinium (FA) lead iodide (CH(NH 2 ) 2 PbI 3 ), FAPI, by contrast preferentially crystallises in the yellow, 2H hexagonal perovskite type polymorph at room temperature, which can be driven to transform to the black cubic perovskite polymorph (required for photovoltaic applications) by heating above room temperature. 16-19Such varying phase behaviour can be accounted for by the different sizes and hydrogen bonding mechanisms of these dissimilar organic cations, MA and FA.Both MA and FA cations display directional hydrogen bonding, a factor of increasing importance in controlling phase behaviour as the system temperature is reduced and also for dening the relative stability of the two polymorphs of FAPI. 20Stabilisation of mixed A site compounds relative to the end members of the series can be rationalised using geometrical arguments in which the perovskite tolerance factor is tuned using differently sized cations, as well as an entrop...

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“…The shapes of the MHP SCs can be controlled by choosing the geometry of the vessel in which crystallization occurs. SCs based on other MHPs, such as MAPbX 3 , FAPbX 3 , and FA 1− x MA x PbX 3 , can be synthesized using ITC.…”

Section: Single Crystals and Light‐emitting Diodesmentioning

confidence: 99%

Metal Halide Perovskites: From Crystal Formations to Light‐Emitting‐Diode Applications

Kim

et al. 2018

Small Methods

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Metal halide perovskites (MHPs) are promising light emitters because they have high color purity, high charge‐carrier mobility, comparable energy levels with organic semiconductors, and the possibility of diverse crystal forms and various crystal formation methods. Since the first report of MHP light‐emitting diodes (PeLEDs) in 2014, many researchers have devoted efforts to increase the luminescence efficiencies of MHPs in various crystal forms, and achieved dramatically improved photoluminescence quantum efficiency of >90% in MHP emitters and external quantum efficiency of ≈14.36% in PeLEDs. Here, the recent progress regarding PeLEDs is reviewed by categorizing MHPs into three types: polycrystalline bulk films, colloidal nanocrystals, and single crystals. The main focus is on photophysical properties, crystallization methods, and mechanisms of various crystal formation, and applications to PeLEDs. Future research directions are also suggested and an outlook for MHP emitters and PeLEDs is given.

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The intrinsic properties of FA_(1−x)MA_xPbI₃ perovskite single crystals

Abstract: We provided a systematical investigation to correlate the crystal structure, composition, mobility, and ion migration behavior to the ratio of MA+/FA+ in FA(1−x)MAxPbI3 single crystal.

Cited by 159 publications

References 41 publications

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX₃ (X = Br, I)

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX₃ (X = Br, I)

Understanding the stability of mixed A-cation lead iodide perovskites

Metal Halide Perovskites: From Crystal Formations to Light‐Emitting‐Diode Applications

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The intrinsic properties of FA(1−x)MAxPbI3 perovskite single crystals

Abstract: We provided a systematical investigation to correlate the crystal structure, composition, mobility, and ion migration behavior to the ratio of MA+/FA+ in FA(1−x)MAxPbI3 single crystal.

Cited by 159 publications

References 41 publications

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX3 (X = Br, I)

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX3 (X = Br, I)

Understanding the stability of mixed A-cation lead iodide perovskites

Metal Halide Perovskites: From Crystal Formations to Light‐Emitting‐Diode Applications

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Product

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The intrinsic properties of FA_(1−x)MA_xPbI₃ perovskite single crystals

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX₃ (X = Br, I)

Suppressing X‐Migrations and Enhancing the Phase Stability of Cubic FAPbX₃ (X = Br, I)