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We synthesize four novel quasi-one-dimensional organic–inorganic hybrid iron chloride compounds (CH3NH3FeCl3, CH(NH2)2FeCl3, C(NH2)3FeCl3, and C3H5N2FeCl3) and characterize their structural and magnetic properties. These materials crystallize in a hexagonal perovskite-type structure, constituting a triangular array of face-sharing iron chloride octahedra chains running along the c-axis, isolated from one another by the organic cation. Through magnetization and heat capacity measurements, we find that the intrachain coupling is weakly ferromagnetic for each variant. Importantly, this work underscores the utility of solid-state chemistry approaches in synthesizing new organic–inorganic hybrid materials.

Magnetically active atomic distances may impact the magnetic ordering in a given system both directly and indirectly. We synthesize three novel quasi-one-dimensional organic–inorganic hybrid cobalt chloride chain compounds (CH3NH3CoCl3, CH(NH2)2CoCl3, and C(NH2)3CoCl3) and characterize their magnetic and thermodynamic properties. These materials crystallize in a hexagonal perovskite-type structure consisting of chains of face-sharing Co–Cl octahedra separated by the respective organic cation. Temperature- and field-dependent magnetic susceptibility analyses reveal that each compound possesses antiferromagnetic intrachain coupling and that the strength of the correlations is comparable across the three materials. Moreover, the interchain Co–Co distance, which depends on the size of the organic cation, is directly related to the temperature at which long-range magnetic ordering occurs.

Bulk CsEuBr3and CsEuCl3are experimentally shown to be magnetic semiconductors that order antiferromagnetically at Néel temperatures of 2.0 K and 1.0 K, respectively. Given that nanoparticles and thin films of CsEuCl3have been reported to order ferromagnetically at a similar temperature, our observation of antiferromagnetic ordering in CsEuBr3and CsEuCl3expands the possible applications of halide perovskites to now include spintronic devices where both ferromagnetic and antiferromagnetic devices can be fabricated from a single material. The conclusion that CsEuCl3can be used as a switchable magnetic material is also supported by our density-functional theory calculations.

In lead(II) halide compounds including virtually all lead halide perovskites, the Pb2+6s lone pair results in distorted octahedra, in accordance with the pseudo-Jahn–Teller effect, rather than generating hemihedral coordination polyhedra. Here, in contrast, we report the characterization of an organic–inorganic hybrid material consisting of one-dimensional edge-sharing chains of Pb–Br square pyramids, separated by [Mn(DMF)6]2+(DMF = dimethylformamide) octahedra. Molecular orbital analysis and density-functional theory calculations indicate that square pyramidal coordination about Pb2+results from the occupancy of the empty ligand site by a Pb2+lone pair that has both s and p orbital character rather than the exclusively 6s lone pair. These results demonstrate that a Pb2+lone pair can be exploited to behave like a ligand in lead halide compounds, greatly expanding the realm of possible lead halide materials to include extended solids with nonoctahedral coordination environments.

Strongly coupled, epitaxially fused colloidal nanocrystal (NC) solids are promising solution-processable semiconductors to realize optoelectronic devices with high carrier mobilities. Here, we demonstrate sequential, solid-state cation exchange reactions to transform epitaxially connected PbSe NC thin films into Cu2Se nanostructured thin-film intermediates and then successfully to achieve zinc-blende, CdSe NC solids with wide epitaxial necking along {100} facets. Transient photoconductivity measurements probe carrier transport at nanometer length scales and show a photoconductance of 0.28(1) cm2V–1s–1, the highest among CdSe NC solids reported. Atomic-layer deposition of a thin Al2O3layer infiltrates and protects the structure from fusing into a polycrystalline thin film during annealing and further improves the photoconductance to 1.71(5) cm2V–1s–1and the diffusion length to 760 nm. We fabricate field-effect transistors to study carrier transport at micron length scales and realize high electron mobilities of 35(3) cm2V–1s–1with on–off ratios of 106after doping.

The design of new chiral materials usually requires stereoselective organic synthesis to create molecules with chiral centers. Less commonly, achiral molecules can self-assemble into chiral materials, despite the absence of intrinsic molecular chirality. Here, we demonstrate the assembly of high-symmetry molecules into a chiral van der Waals structure by synthesizing crystals of C60(SnI4)2from icosahedral buckminsterfullerene (C60) and tetrahedral SnI4molecules through spontaneous self-assembly. The SnI4tetrahedra template the Sn atoms into a chiral cubic three-connected net of the SrSi2type. Our results represent the remarkable emergence of a self-assembled chiral material from two of the most highly symmetric molecules, demonstrating that almost any molecular, nanocrystalline, or engineered precursor can be considered when designing chiral assemblies.

We report a family of two-dimensional hybrid perovskites (2DHPs) based on phenethylammonium lead iodide ((PEA)2PbI4) that show complex structure in their low-temperature excitonic absorption and photoluminescence (PL) spectra as well as hot exciton PL. We replace the 2-position (ortho) H on the phenyl group of the PEA cation with F, Cl, or Br to systematically increase the cation’s cross-sectional area and mass and study changes in the excitonic structure. These single atom substitutions substantially change the observable number of and spacing between discrete resonances in the excitonic absorption and PL spectra and drastically increase the amount of hot exciton PL that violates Kasha’s rule by over an order of magnitude. To fit the progressively larger cations, the inorganic framework distorts and is strained, reducing the Pb–I–Pb bond angles and increasing the 2DHP band gap. Correlation between the 2DHP structure and steady-state and time-resolved spectra suggests the complex structure of resonances arises from one or two manifolds of states, depending on the 2DHP Pb–I–Pb bond angle (as)symmetry, and the resonances within a manifold are regularly spaced with an energy separation that decreases as the mass of the cation increases. The uniform separation between resonances and the dynamics that show excitons can only relax to the next-lowest state are consistent with a vibronic progression caused by a vibrational mode on the cation. These results demonstrate that simple changes to the cation can be used to tailor the properties and dynamics of the confined excitons without directly modifying the inorganic framework.

We use a solid-state method to synthesize single crystals of perovskite-phase cesium lead iodide (γ-CsPbI3) that are kinetically stable at room temperature. Single crystal X-ray diffraction characterization shows the compound is orthorhombic with the GdFeO3structure at room temperature. Unlike conventional semiconductors, the optical absorption and joint density-of-states of bulk γ-CsPbI3is greatest near the band edge and decreases beyond the Egfor at least 1.9 eV. Bulk γ-CsPbI3does not show an excitonic resonance and has an optical band gap of 1.63(3) eV, ∼90 meV smaller than has been reported in thin films; these and other differences indicate that previously measured thin film γ-CsPbI3shows signatures of quantum confinement. By flowing gases in situduring powder X-ray diffraction measurements, we confirm that γ-CsPbI3is stable to oxygen but rapidly and catalytically converts to non-perovskite δ-CsPbI3in the presence of moisture. Our results provide vital parameters for theoretical and experimental investigations into perovskite-phase CsPbI3that will the guide the design and synthesis of atmospherically stable inorganic halide perovskites.

Colloidal semiconductor nanocrystals (NCs) are a promising materials class for solution-processable, next-generation electronic devices. However, most high-performance devices and circuits have been achieved using NCs containing toxic elements, which may limit their further device development. We fabricate high mobility CuInSe2NC field-effect transistors (FETs) using a solution-based, post-deposition, sequential cation exchange process that starts with electronically coupled, thiocyanate (SCN)-capped CdSe NC thin films. First Cu+is substituted for Cd2+transforming CdSe NCs to Cu-rich Cu2Se NC films. Next, Cu2Se NC films are dipped into a Na2Se solution to Se-enrich the NCs, thus compensating the Cu-rich surface, promoting fusion of the Cu2Se NCs, and providing sites for subsequent In-dopants. The liquid-coordination-complex trioctylphosphine–indium chloride (TOP–InCl3) is used as a source of In3+to partially exchange and n-dope CuInSe2NC films. We demonstrate Al2O3-encapsulated, air-stable CuInSe2NC FETs with linear (saturation) electron mobilities of 8.2 ± 1.8 cm2/(V s) (10.5 ± 2.4 cm2/(V s)) and with current modulation of 105, comparable to that for high-performance Cd-, Pb-, and As-based NC FETs. The CuInSe2NC FETs are used as building blocks of integrated inverters to demonstrate their promise for low-cost, low-toxicity NC circuits.

We synthesize and characterize the magnetic and thermodynamic properties of the quasi one-dimensional organic–inorganic hybrid ANiCl3compounds [A = N(CH3)4+, CH3NH3+, (CH3)2NH2+, C(NH2)3+, and CH(NH2)2+]. Additionally, the crystal structure of (CH3)2NH2NiCl3is reported. These materials possess chains of face-sharing NiCl6octahedra in a triangular array. The chains run in one direction and are separated from one another by organic cations of different sizes and geometries. In accordance with the 90° superexchange model, we find that the nature of the magnetic coupling within chains can be predicted by the value of the Ni–Cl–Ni angle. As the Ni–Cl–Ni angle decreases from 90°, the magnetic interactions become increasingly antiferromagnetic. These findings provide a foundation for predicting the magnetic properties of quasi one-dimensional organic–inorganic hybrid ANiCl3compounds.

We find evidence for the formation and relaxation of large exciton polarons in 2D organic–inorganic hybrid perovskites. Using ps-scale time-resolved photoluminescence within the phenethylammonium lead iodide family of compounds, we identify a red shifting of emission that we associate with exciton polaron formation time scales of 3–10 ps. Atomic substitutions of the phenethylammonium cation allow local control over the structure of the inorganic lattice, and we show that the structural differences among materials strongly influence the exciton polaron relaxation process, revealing a polaron binding energy that grows larger (up to 15 meV) in more strongly distorted compounds.

The ability to continuously tune the band gap of a semiconductor allows its optical properties to be precisely tailored for specific applications. We demonstrate that the band gap of the halide perovskite CsPbBr3can be continuously widened through homovalent substitution of Sr2+for Pb2+using solid-state synthesis, creating a material with the formula CsPb1–xSrxBr3(0 ≤ x≤ 1). Sr2+and Pb2+form a solid solution in CsPb1–xSrxBr3. Pure CsPbBr3has a band gap of 2.29(2) eV, which increases to 2.64(3) eV for CsPb0.25Sr0.75Br3. The increase in band gap is clearly visible in the color change of the materials and is also confirmed by a shift in the photoluminescence. Density-functional theory calculations support the hypothesis that Sr incorporation widens the band gap without introducing mid-gap defect states. These results demonstrate that homovalent B-site alloying can be a viable method to tune the band gap of simple halide perovskites for absorptive and emissive applications such as color-tunable light-emitting diodes, tandem solar cells, and photodetectors.

We describe the spontaneous chiral self-assembly of C70with SnI4as well as a mixture of C60and C70with SnI4. Macroscopic single crystals with the formula (C70)x(C60)1–x(SnI4)2(x= 0–1) are reported. C60,which is spherical, and C70, which is ellipsoidal, form a solid solution in these crystals, and the cubic lattice parameter of the chiral phase linearly increases as xgrows from 0 to 1 in accordance with Vegard’s law. Our results demonstrate that nonspherical particles and polydispersity are not an impediment to the growth of chiral crystals from high-symmetry achiral precursors, providing a route to assemble achiral particles including colloidal nanocrystals and engineered nanostructures into chiral materials without the need to use external templates or forces.