Mixology of MA1–xEAxPbI3 Hybrid Perovskites: Phase Transitions, Cation Dynamics, and Photoluminescence
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ABSTRACT:
SUBMITTER: Simenas M
PROVIDER: S-EPMC9686138 | biostudies-literature | 2022 Nov
REPOSITORIES: biostudies-literature
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Project description:The rotational dynamics of an organic cation in hybrid halide perovskites is intricately linked to the phase transitions that are known to occur in these materials; however, the exact relation is not clear. We have performed detailed model studies on methylammonium lead iodide and formamidinium lead iodide to unravel the relation between rotational dynamics and phase behavior. We show that the occurrence of the phase transitions is due to a subtle interplay between dipole-dipole interactions between the organic cations, specific (hydrogen bonding) interactions between the organic cation and the lead iodide lattice, and deformation of the lead iodide lattice in reaction to the reduced rotational motion of the organic cations. This combination of factors results in phase transitions at specific temperatures, leading to the formation of large organized domains of dipoles. The latter can have significant effects on the electronic structure of these materials.
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Project description:Recently, a number of variations to the hybrid perovskite structure have been suggested in order to improve on the properties of methylammonium lead iodide, the archetypical hybrid halide perovskite material. In particular, with respect to the chemical stability of the material, steps should be taken. We performed an in-depth analysis of the structure of MAPbI3 upon incorporation of dimethylammonium (DMA) in order to probe the integrity of the perovskite lattice in relation to changes in the organic cation. This material, with formula MA1-xDMAxPbI3, adopts a 3D perovskite structure for 0 < x < 0.2, while a nonperovskite yellow phase is formed for 0.72 < x < 1. In the perovskite phase, the methylammonium and dimethylammonium ions are distributed randomly throughout the lattice. For 0.05 < x < 0.2, the phase-transition temperature of the material is lowered when compared to that of pure MAPbI3 (x = 0). The material, although disordered, has apparent cubic symmetry at room temperature. This leads to a small increase in the band gap of the material of about 20 meV. Using 14N NMR relaxation experiments, the reorientation times of the MA and DMA cations in MA0.8DMA0.2PbI3 were established to be 1.6 and 2.6 ps, respectively, indicating that both ions are very mobile in this material, on par with the MA ions in MAPbI3. All of the produced MA1-xDMAxPbI3 materials were richer in DMA than the precursor solution from which they were crystallized, indicating that DMA incorporation is energetically favorable and suggesting a higher thermodynamic stability of these materials when compared to that of pure MAPbI3.
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Project description:Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles.
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Project description:Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs y FA1-y Pb(Br x I1-x )3 using low-temperature in situ synchrotron powder X-ray diffraction. Our findings revealed that substituting the I anion with Br in mixed-cation (Cs,FA) perovskites suppressed the phase transformation from tetragonal to orthorhombic at low temperatures. The addition of Br also prevented the formation of nonperovskite secondary phases. We gained fundamental insights into the structural behavior of these materials by creating a low-temperature phase diagram for the compositional set of mixed-cation mixed-halides. This understanding of the structural properties lays the groundwork for designing more robust and efficient energy materials capable of functioning under extreme temperature conditions, including space-based solar energy conversion.
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Project description:Hybrid organic-inorganic perovskites exhibit high photovoltaic performance and other novel photonic functions. While polaron formation is believed to facilitate efficient carrier transport, the elementary processes of the underlying electron-lattice coupling are yet poorly understood because of the multiscale chemical and structural heterogeneities. Here, we resolve in combined ground- and excited-state spatiospectral ultrafast nanoimaging how structural characteristics are related to both molecular cation and polaron dynamics. We use the observed nanoscale spatial variations of the formamidinium (FA) cation transient vibrational blue shifts as a local probe of the nonlocal polaron-cation coupling. From the correlation with nanomovies of the polaron dynamics, we then infer how a softer more polarizable lattice supports stable polarons and longer-lived residual carriers. This, together with a relative intragrain homogeneity in contrast to high intergrain heterogeneity, suggests pathways for improved synthesis and device engineering, and that perovskite photonics performance is still far from any fundamental limits.
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Project description:Hybrid organic-inorganic perovskites exhibit remarkable potential as cost-effective and high-efficiency materials for photovoltaic applications. Their exceptional chemical tunability opens further routes for optimizing their optical and electronic properties through structural engineering. Nevertheless, the extraordinary softness of the lattice, stemming from its interconnected organic-inorganic composition, unveils formidable challenges in structural characterization. Here, by focusing on the quintessential methylammonium lead triiodide, MAPbI3, we combine first-principles modeling with high-resolution neutron scattering data to identify the key stationary points on its shallow potential energy landscape. This combined experimental and computational approach enables us to benchmark the performance of a collection of semilocal exchange-correlation functionals and to track the local distortions of the perovskite framework, hallmarked by the inelastic neutron scattering response of the organic cation. By conducting a thorough examination of structural distortions, we introduce the IKUR-PVP-1 structural data set. This data set contains nine mechanically stable structural models, each manifesting a distinct vibrational response. IKUR-PVP-1 constitutes a valuable resource for assessing thermal behavior in the low-temperature perovskite phase. In addition, it paves the way for the development of accurate force fields, enabling a comprehensive understanding of the interplay between the structure and dynamics in MAPbI3 and related hybrid perovskites.
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Project description:Lead halide perovskites are extensively investigated as efficient solution-processable materials for photovoltaic applications. The greatest stability and performance of these compounds are achieved by mixing different ions at all three sites of the APbX3 structure. Despite the extensive use of mixed lead halide perovskites in photovoltaic devices, a detailed and systematic understanding of the mixing-induced effects on the structural and dynamic aspects of these materials is still lacking. The goal of this review is to summarize the current state of knowledge on mixing effects on the structural phase transitions, crystal symmetry, cation and lattice dynamics, and phase diagrams of three- and low-dimensional lead halide perovskites. This review analyzes different mixing recipes and ingredients providing a comprehensive picture of mixing effects and their relation to the attractive properties of these materials.
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Project description:Hybrid perovskite semiconductor materials are predicted to lock chirality into place and encode asymmetry into their electronic states, while softness of their crystal lattice accommodates lattice strain to maintain high crystal quality with low defect densities, necessary for high luminescence yields. We report photoluminescence quantum efficiencies as high as 39% and degrees of circularly polarized photoluminescence of up to 52%, at room temperature, in the chiral layered hybrid lead-halide perovskites (R/S/Rac)-3BrMBA2PbI4 [3BrMBA = 1-(3-bromphenyl)-ethylamine]. Using transient chiroptical spectroscopy, we explain the excellent photoluminescence yields from suppression of nonradiative loss channels and high rates of radiative recombination. We further find that photoexcitations show polarization lifetimes that exceed the time scales of radiative decays, which rationalize the high degrees of polarized luminescence. Our findings pave the way toward high-performance solution-processed photonic systems for chiroptical applications and chiral-spintronic logic at room temperature.
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Project description:The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH2)2PbI3 (FAPbI3) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH3NH3PbI3 (MAPbI3) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI3/FAPbI3 structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI3/FAPbI3 is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI3/FAPbI3. More importantly, compare with the un-doped tetragonal MAPbI3/FAPbI3, the Sn-doped MAPbI3 and FAPbI3 have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sn-doped FAPbI3. The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI3 make it promising candidates for high-efficient perovskite cells.
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Project description:The study of MAPbI3 phase transitions based on temperature-dependent optical spectroscopy has recently gained a huge attention. Photoluminescence (PL) investigations of the tetragonal-orthorhombic transition suggest that tetragonal nanodomains are present below the transition temperature and signatures associated with tetragonal segregations are observed. We have studied the impact of phase nanosegregation across the orthorhombic-tetragonal phase transition of MAPbI3 on the system's properties employing a tight binding (TB) approach. The particle swarm optimization has been used to obtain a consistent set of TB parameters, where the target properties of the system have been derived by first-principles calculations. The theoretical results have been compared with the measured PL spectra for a temperature range going from 10 to 100 K. Our model effectively captures the carriers' localization phenomenon induced by the presence of residual tetragonal nanodomains and demonstrates that the assumption of phase nanosegregation can explain the low-energy features in the PL spectra of MAPbI3.
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