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At least 1,621 records · Page 90
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DOE OSTI2021

Zero-Dimensional Hybrid Organic–Inorganic Indium Bromide with Blue Emission

Low-dimensional hybrid organic–inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. In this work, we report a new zero-dimensional hybrid organic–inorganic halide, RInBr 4 , featuring photoemissive trimethyl(4-stilbenyl)methylammonium (R + ) cations and nonemissive InBr 4 – tetrahedral anions. The crystal structure of RInBr 4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l’Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In(III) halides for light emission applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Data-Driven Mapping of the Cesium Cadmium Bromide Phase Space Utilizing a Soft-Chemistry Approach

Soft-chemistry techniques provide a versatile approach to synthesizing inorganic materials under mild conditions, enabling access to compositions and structures that are challenging to achieve through traditional thermodynamically driven solid-state methods. However, these solution-based routes often result in phase competition, requiring precise control over reaction conditions to achieve selective product formation. While one-variable-at-a-time (OVAT) approaches have traditionally been used for phase selection, data-driven strategies are emerging as more efficient methods for navigating complex synthetic spaces. Ternary metal halides, such as cesium cadmium bromides (Cs–Cd–Br), are of growing interest due to their potential in wide and ultrawide band gap applications. Unlike the well-studied cesium lead halide phases, the compositional diversity and solution-based synthesis of ternary Cs–Cd–Br phases remain largely unexplored. This study systematically investigates the synthetic phase space of the Cs–Cd–Br system by constructing a data-driven phase map. Using a common set of precursors and a standardized experimental procedure, we successfully synthesize all four known Cs–Cd–Br phases—CsCdBr 3 , Cs 2 CdBr 4 , Cs 3 CdBr 5 , and Cs 7 Cd 3 Br 13 —each exhibiting distinct structures, morphologies, and optical properties. Our findings highlight the potential of soft-chemistry methods for expanding the library of ternary metal halides and provide key insights into the thermodynamic and kinetic factors governing phase formation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Structural Diversity and Tunable Emission in Hybrid Organic–Inorganic Copper(I) Bromides

Recently, hybrid organic−inorganic copper(I) metal halides have attracted global attention due to their intriguing optical properties and low-cost solution processability. In this work, we report three hybrid organic−inorganic copper(I) bromides, [TMPA] 2 [Cu 2 Br 4 ], [TMPA] 4 [Cu 6 Br 10 ], and [TMPA] 2 [Cu 4 Br 6 ], synthesized through a slow evaporation method using trimethylphenylammonium (TMPA + ) as the organic cation. By precise control of the CuBr and TMPABr precursors, different copper halide [Cu 2 Br 4 ] 2− , [Cu 6 Br 10 ] 4− , and [Cu 4 Br 6 ] 2− structural units can be obtained. [TMPA] 2 [Cu 2 Br 4 ], [TMPA] 4 [Cu 6 Br 10 ], and [TMPA] 2 [Cu 4 Br 6 ] demonstrate distinct blue, orange, and greenish-yellow light emission, respectively. The first two compounds have zero-dimensional (0D) crystal structures in centrosymmetric triclinic space group P-1 and monoclinic space group P2 1 /n. In contrast, [TMPA] 2 [Cu 4 Br 6 ] features a unique one-dimensional (1D) structure and crystallizes in the centrosymmetric monoclinic space group P2 1 /c. Consequently, the observed greenish-yellow emission of [TMPA] 2 [Cu 4 Br 6 ] is also unique, in contrast to the typical orange-red emission of 0D [Cu 4 Br 6 ]-based compounds. This work provides insights into the design of copper halide light emitters and emphasizes the influence of structural dimensionality on photoluminescence. The tunable optical properties suggest the potential of these materials for multicolor photopatterning, information encryption, and anticounterfeiting applications.

Anions↗
DOE OSTI2021

Material, Phase, and Interface Stability of Photovoltaic Perovskite: A Perspective

The past decade has witnessed the unprecedented boost of power conversion efficiency (PCE) of photovoltaics based on halide perovskite materials since its early discovery. Despite its remarkably good performance, long-term stability is yet one of the last barriers before commercializing halide perovskite photovoltaics is possible. In this perspective, we discuss the challenges and concurrently the strategies regarding the stability of the perovskite materials, photoactive crystal phases, and the performance as well as stability limiting interfaces. Future perspectives of stable halide perovskite and perovskite solar cells are also proposed to shine light on letting perovskite technology satisfy long-term operation warranty.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Lattice Dynamics and Optoelectronic Properties of Vacancy-Ordered Double Perovskite Cs 2 TeX 6 (X = Cl – , Br – , I – ) Single Crystals

The soft, dynamic lattice of inorganic lead halide perovskite CsPbX 3 (X = Cl ⁻ , Br ⁻ , I ⁻ ) leads to the emergence of many interesting photophysical and optoelectronic phenomena. However, probing their lattice dynamics with vibrational spectroscopy remains challenging. The influence of the fundamental octahedral building block in the perovskite lattice can be better resolved in zero-dimensional (0D) vacancy-ordered double perovskites of form A 2 BX 6 . Here we study Cs 2 TeX 6 (X = Cl ⁻ , Br ⁻ , I ⁻ ) single crystals to yield detailed insight into the fundamental octahedral building block and to explore the effect that its isolation in the crystal structure has on structural and electronic properties. The isolated [TeX 6 ] 2- octahedral units serve as the vibrational, absorbing, and emitting centers within the crystal. Serving as the vibrational centers, the isolated octahedra inform the likelihood of a random distribution of 10 octahedral symmetries within the mixed-halide spaces, as well as the presence of strong exciton-phonon coupling and anharmonic lattice dynamics. Serving as the absorbing and emitting centers, the isolated octahedra exhibit compositionally tunable absorption (1.50-3.15 eV) and emission (1.31-2.11 eV) energies. Due to greater molecular orbital overlap between neighboring octahedra with increasing halide anion size, there is a transition from a more molecule-like electronic structure in Cs 2 TeCl 6 and Cs 2 TeBr 6 -as expected from the effective 0D nature of these single crystals-to a dispersive electronic structure in Cs 2 TeI 6 , typical of three-dimensional (3D) bulk single crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Systematic Characterization on Optical and Phonon Properties of Cs[Pb x Sn 1– x ]I 3 Alloyed Perovskites via First-Principles Modeling

Here, understanding the optical properties and phonon thermodynamic features of materials enables the determination of their viability for optoelectronic applications including optical-based gas sensors. Metal halide perovskites ABX 3 as well as their mixed alloys can be attractive in applications of this kind. In particular, the formation of alloyed perovskites A[B x B’ 1–x ]X 3 modulates the functional characteristics that can overtake the single-halide ABX 3 . To this end, we use the first-principles simulations to model the effect of B-site alloying on the optical and phonon properties of cubic Cs[Pb x Sn 1–x ]I 3 (x = 0.75, 0.50, and 0.25). We identified the systematic shifts of optical properties as a function of alloying concentration, such as dielectric constants, refraction indices, and absorption coefficients. It was also found that a linear correlation exists between the optical constants and the band gaps of these materials, which satisfies the Penn model. Modeling of phonons in Cs[Pb x Sn 1–x ]I 3 showed that dissipating the dynamically unstable phonons can be feasible at a carefully chosen alloying concentration, which are originally present in their single-halide Pb- and Sn-ends. Our findings pave a way to optimize the alloying conditions of the alloyed perovskite systems of interest for tuning their optical and phonon stability characteristics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Many-Exciton Quantum Dynamics in a Ruddlesden–Popper Tin Iodide

We present a study on the many-body exciton interactions in a Ruddlesden–Popper tin halide, namely, (PEA) 2 SnI 4 (PEA = phenylethylammonium), using coherent two-dimensional electronic spectroscopy. The optical dephasing times of the third-order polarization observed in these systems are determined by exciton many-body interactions and lattice fluctuations. We investigate the excitation-induced dephasing (EID) and observe a significant reduction of the dephasing time with increasing excitation density as compared to its lead counterpart (PEA) 2 PbI 4 , which we have previously reported in a separate publication [J. Chem. Phys. 2020, 153, 164706]. Surprisingly, we find that the EID interaction parameter is four orders of magnitude higher in (PEA) 2 SnI 4 than that in (PEA) 2 PbI 4 . This increase in the EID rate may be due to exciton localization arising from a more statically disordered lattice in the tin derivative. This is supported by the observation of multiple closely spaced exciton states and the broadening of the linewidth with increasing population time (spectral diffusion), which suggests a static disordered structure relative to the highly dynamic lead-halide. Additionally, we find that the exciton nonlinear coherent lineshape shows evidence of a biexcitonic state with low binding energy (<10 meV) not observed in the lead system. We model the lineshapes based on a stochastic scattering theory that accounts for the interaction with a nonstationary population of dark background excitations. Our study provides evidence of differences in the exciton quantum dynamics between tin- and lead-based Ruddlesden–Popper metal halides (RPMHs) and links them to the exciton–exciton interaction strength and the static disorder aspect of the crystalline structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Nanoscale Photoexcited Carrier Dynamics in Perovskites

The optoelectronic properties of lead halide perovskite thin films can be tuned through compositional variations and strain, but the associated nanocrystalline structure makes it difficult to untangle the link between composition, processing conditions, and ultimately material properties and degradation. Here, we study the effect of processing conditions and degradation on the local photoconductivity dynamics in [(CsPbI 3 ) 0.05 (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 ] and (FA 0.7 Cs 0.3 PbI 3 ) perovskite thin films using temporally and spectrally resolved microwave near-field microscopy with a temporal resolution as high as 5 ns and a spatial resolution better than 50 nm. For the latter FACs formulation, we find a clear effect of the process annealing temperature on film morphology, stability, and spatial photoconductivity distribution. After exposure of samples to ambient conditions and illumination, we find spectral evidence of halide segregation-induced degradation below the instrument resolution limit for the mixed halide formulation, while we find a clear spatially inhomogeneous increase in the carrier lifetime for the FACs formulation annealed at 180 degrees C.

14 SOLAR ENERGY↗
DOE OSTI2018

Why Two Metals Are Better Than One for Heterodinuclear Cobalt–Zirconium-Catalyzed Kumada Coupling

Heterodinuclear transition metal complexes with a direct metal–metal interaction offer the potential of unique reactivity compared with mononuclear catalysts. Heterodinuclear Co–Zr complexes with phosphinoamide ligands bridging Co and Zr metal centers are effective precatalysts for Kumada C–C bond coupling reactions between alkyl halides and alkyl Grignards. On the other hand, the analogous mononuclear Co tris(phosphinoamine) complex without Zr provides very inefficient catalysis. Here we describe density functional theory calculations that reveal the mechanistic and reactivity impact of the Co–Zr metal–metal interaction and phosphinoamide ligands on alkyl halide–alkyl Grignard Kumada coupling catalysis. The Co–Zr interaction enables two-electron reduction of the precatalyst to form an active catalyst, which then allows a low-energy electron-transfer alkyl halide oxidative addition mechanism. The Co–Zr interaction and the phosphinoamide ligands bridging the metal centers provide a dialkyl intermediate with a low-energy C–C bond forming reductive elimination route through a phosphine dissociation pathway, which is not viable for an analogous mononuclear Co complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Piperazine Suppresses Self-Doping in CsSnI 3 Perovskite Solar Cells

Tin-based halide perovskite materials are promising candidates for lead-free halide perovskite solar cells. However, they suffer from poor device reproducibility and limited overall power conversion efficiencies due to their tendency to become semimetallic from p-type defect states. Herein, we demonstrate an effective approach to address this issue via the addition of piperazine to the precursor solution of tin-based halide perovskite films, to suppress the undesirable p-doping of CsSnI 3 films. Piperazine is found to significantly reduce the conductivity of CsSnI 3 films, improve the film coverage, and at the same time suppress the crystallization of excess SnI 2 . Consequently, short-circuit behaviors are eliminated, with significantly improved CsSnI 3 solar-cell performance. Finally, the effects of incorporating SnCl 2 and SnF 2 into the CsSnI 3 devices were investigated in conjunction with addition of piperazine to achieve CsSnI 3 devices with a maximum power conversion efficiency of 3.83%.

14 SOLAR ENERGY↗
DOE OSTI2020

Water-Stable 1D Hybrid Tin(II) Iodide Emits Broad Light with 36% Photoluminescence Quantum Efficiency

The optical and light emission properties of tin and lead halide perovskites are remarkable because of the robust room-temperature (RT) performance, broad wavelength tunability, high efficiency, and good quenching resistance to defects. These highly desirable attributes promise to transform current light-emitting devices, phosphors, and lasers. One disadvantage in most of these materials is the sensitivity to moisture. Here, we report a new air-stable one-dimensional (1D) hybrid lead-free halide material (DAO)Sn 2 I 6 (DAO, 1,8-octyldiammonium) that is resistant to water for more than 15 h. The material exhibits a sharp optical absorption edge at 2.70 eV and a strong broad orange light emission centered at 634 nm, with a full width at half-maximum (fwhm) of 142 nm (0.44 eV). The emission has a long photoluminescence (PL) lifetime of 582 ns, while the intensity is constant over a very broad temperature range (145–415 K) with a photoluminescence quantum yield (PLQY) of at least 20.3% at RT. Above 415 K the material undergoes a structural phase transition from monoclinic (C2/c) to orthorhombic (Ibam) accompanied by a red shift in the band gap and a quench in the photoluminescence emission. Density functional theory calculations support the trend in the optical properties and the 1D electronic nature of the structure, where the calculated carrier effective masses along the inorganic chain are significantly lower than those perpendicular to the chain. As a result, thin films of the compound readily fabricated from solutions exhibit the same optical properties, but with improved PLQY of 36%, for a 60 nm thick film, among the highest reported for lead-free low-dimensional 2D and 1D perovskites and metal halides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Tunable Broad Light Emission from 3D “Hollow” Bromide Perovskites through Defect Engineering

We report hybrid halide perovskites consisting of corner-sharing metal halide octahedra and small cuboctahedral cages filled with counter cations have proven to be prominent candidates for many high-performance optoelectronic devices. The stability limits of their three-dimensional perovskite framework are defined by the size range of the cations present in the cages of the structure. In some cases, the stability of the perovskite-type structure can be extended even when the counterions violate the size and shape requirements, as is the case in the so-called "hollow" perovskites. In this work, we engineered a new family of 3D highly defective yet crystalline "hollow" bromide perovskites with general formula (FA) 1-x (en) x (Pb) 1-0.7x (Br) 3-0.4x (FA = formamidinium (FA + ), en = ethylenediammonium (en 2+ ), x = 0-0.44). Pair distribution function analysis shed light on the local structural coherence, revealing a wide distribution of Pb-Pb distances in the crystal structure as a consequence of the Pb/Br-deficient nature and en inclusion in the lattice. By manipulating the number of Pb/Br vacancies, we finely tune the optical properties of the pristine FAPbBr 3 by blue shifting the band gap from 2.20 to 2.60 eV for the x = 0.42 en sample. A most unexpected outcome was that at x > 0.33 en incorporation, the material exhibits strong broad light emission (1% photoluminescence quantum yield (PLQY)) that is maintained after exposure to air for more than a year. This is the first example of strong broad light emission from a 3D hybrid halide perovskite, demonstrating that meticulous defect engineering is an excellent tool for customizing the optical properties of these semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Emerging Two-Dimensional Organic Semiconductor-Incorporated Perovskites–A Fascinating Family of Hybrid Electronic Materials

Halide perovskites have attracted a great amount of attention owing to their unique materials chemistry, excellent electronic properties, and low-cost manufacturing. Two-dimensional (2D) halide perovskites, originating from three-dimensional (3D) perovskite structures, are structurally more diverse and therefore create functional possibilities beyond 3D perovskites. The much less restrictive size constraints on the organic component of these hybrid materials particularly provide an exciting platform for designing unprecedented materials and functionalities at the molecular level. In this Perspective, we discuss the concept and recent development of a sub-class of 2D perovskites, namely, organic semiconductor-incorporated perovskites (OSiPs). OSiPs combine the electronic functionality of organic semiconductors with the soft and dynamic halide perovskite lattice, offering opportunities for tailoring the energy landscape, lattice and carrier dynamics, and electron/ion transport properties for various fundamental studies, as well as device applications. Specifically, we summarize recent advances in the design, synthesis, and structural analysis of OSiPs with various organic conjugated moieties as well as the application of OSiPs in photovoltaics, light-emitting devices, and transistors. As a result, challenges and further opportunities for OSiPs in molecular design, integration of novel functionality, film quality, and stability issues are addressed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Structural Evolution and Photoluminescence Quenching across the FASnI 3– x Br x ( x = 0–3) Perovskites

One of the primary methods for band gap tuning in metal halide perovskites has been halide (I/Br) mixing. Despite widespread usage of this type of chemical substitution in perovskite photovoltaics, there is still little understanding of the structural impacts of halide alloying, with the assumption being the formation of ideal solid solutions. The FASnI 3–x Br x (x = 0–3) family of compounds provides the first example where the assumption breaks down, as the composition space is broken into two unique regimes (x = 0–2.9; x = 2.9–3) based on their average structure with the former having a 3D and the latter having an extended 3D (pseudo 0D) structure. Pair distribution function (PDF) analyses further suggest a dynamic 5s 2 lone pair expression resulting in increasing levels of off-centering of the central Sn as the Br concentration is increased. These antiferroelectric distortions indicate that even the x = 0–2.9 phase space behaves as a nonideal solid-solution on a more local scale. Solid-state NMR confirms the difference in local structure yielding greater insight into the chemical nature and local distributions of the FA + cation. In contrast to the FAPbI 3–x Br x series, a drastic photoluminescence (PL) quenching is observed with x ≥ 1.9 compounds having no observable PL. In conclusion, our detailed studies attribute this quenching to structural transitions induced by the distortions of the [SnBr 6 ] octahedra in response to stereochemically expressed lone pairs of electrons. This is confirmed through density functional theory, having a direct impact on the electronic structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cage Balancing Enhances Optoelectronic and Lasing Performance in Stable Quasi-2D Tin Iodide Perovskites

Two-dimensional (2D) tin halide perovskites are highly tunable and low-toxicity semiconductors, promising for next-generation optoelectronics. However, achieving air stability and excellent photophysical properties simultaneously necessitates deliberate structure tuning using organic spacer cations and A-site cations. Here, we report a series of new quasi-2D Ruddlesden–Popper tin halide perovskites using a fluorinated aromatic spacer cation, 4-fluorophenethylammonium (4FPEA), and systematically investigate the impacts of layer thickness, spacer cation, and A-site cation on the crystal structures and optical properties of (4FPEA) 2 (A) n−1 S n I 3n+1 . These 4FPEA-based 2D tin perovskites, further tuned by the A-cations, exhibit uniquely undistorted 180° out-of-plane Sn–I–Sn bond angles and low octahedral distortions compared to other quasi-2D perovskites and demonstrate prolonged air stability, excellent photophysics, and amplified spontaneous emission and lasing in exfoliated microflakes. A comprehensive survey of reported n = 2 lead and tin iodide perovskites reveals that all structures can be classified into three types (tilted, balanced, and buckled) based on the structural distortion parameters of their perovskite cages. Notably, (4FPEA) 2 (A)Sn 2 I 7 are among the handful of “balanced” n = 2 perovskites with minimal distortion and excellent optoelectronic performance. Furthermore, the structural insights and cage-balancing approach revealed herein motivate the deliberate design of quasi-2D perovskites through the synergy of the spacer and cage cations, further paving the way for high-performance optoelectronic applications of stable tin halide perovskites.

Cations↗
DOE OSTI2024

Large exchange-driven intrinsic circular dichroism of a chiral 2D hybrid perovskite

Abstract In two-dimensional chiral metal-halide perovskites, chiral organic spacers endow structural and optical chirality to the metal-halide sublattice, enabling exquisite control of light, charge, and electron spin. The chiroptical properties of metal-halide perovskites have been measured by transmissive circular dichroism spectroscopy, which necessitates thin-film samples. Here, by developing a reflection-based approach, we characterize the intrinsic, circular polarization-dependent complex refractive index for a prototypical two-dimensional chiral lead-bromide perovskite and report large circular dichroism for single crystals. Comparison with ab initio theory reveals the large circular dichroism arises from the inorganic sublattice rather than the chiral ligand and is an excitonic phenomenon driven by electron-hole exchange interactions, which breaks the degeneracy of transitions between Rashba-Dresselhaus-split bands, resulting in a Cotton effect. Our study suggests that previous data for spin-coated films largely underestimate the optical chirality and provides quantitative insights into the intrinsic optical properties of chiral perovskites for chiroptical and spintronic applications.

25 ENERGY STORAGE↗
DOE OSTI2024

Unravelling ultralow thermal conductivity in perovskite Cs2AgBiBr6: dominant wave-like phonon tunnelling and strong anharmonicity

Abstract Understanding the lattice dynamics and heat transport physics in the lead-free halide double perovskites remains an outstanding challenge due to their lattice dynamical instability and strong anharmonicity. In this work, we investigate the microscopic mechanisms of anharmonic lattice dynamics and thermal transport in lead-free halide double perovskite Cs 2 AgBiBr 6 from first principles. We combine self-consistent phonon calculations with bubble diagram correction and a unified theory of lattice thermal transport that considers both the particle-like phonon propagation and wave-like tunnelling of phonons. An ultra-low thermal conductivity at room temperature (~0.21 Wm −1 K −1 ) is predicted with weak temperature dependence( ~ T −0.34 ), in sharp contrast to the conventional ~T −1 dependence. Particularly, the vibrational properties of Cs 2 AgBiBr 6 are featured by strong anharmonicity and wave-like tunnelling of phonons. Anharmonic phonon renormalization from both the cubic and quartic anharmonicities are found essential in precisely predicting the phase transition temperature in Cs 2 AgBiBr 6 while the negative phonon energy shifts induced by cubic anharmonicity has a significant influence on particle-like phonon propagation. Further, the contribution of the wave-like tunnelling to the total thermal conductivity surpasses that of the particle-like propagation above around 310 K, indicating the breakdown of the phonon gas picture conventionally used in the Peierls-Boltzmann Transport Equation. Importantly, further including four-phonon scatterings is required in achieving the dominance of wave-like tunnelling, as compared to the dominant particle-like propagation channel when considering only three-phonon scatterings. Our work highlights the importance of lattice anharmonicity and wave-like tunnelling of phonons in the thermal transport in lead-free halide double perovskites.

Chemistry↗