Amidination of ligands for chemical and field-effect passivation stabilizes perovskite solar cells.

Surface passivation has driven the rapid increase in the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, state-of-the-art surface passivation techniques rely on ammonium ligands that suffer deprotonation under light and thermal stress. We developed a library of amidinium ligands, of interest for their resonance effect-enhanced N-H bonds that may resist deprotonation, to increase the thermal stability of passivation layers on perovskite surfaces.

The development and impact of tin selenide on thermoelectrics.

Thermoelectric technology experienced rapid development over the past 20 years, with the most promising applications being in both power generation and active cooling. Among existing thermoelectrics, tin selenide (SnSe) has had particularly rapid development owing to the unexpectedly high thermoelectric efficiency that has been continuously established over the past decade. Several transport mechanisms and strategies used to interpret and improve the thermoelectric performance of SnSe have been important for understanding and developing other material systems with SnSe-like characteristics.

Chemical Pressure-Driven Band Convergence and Discordant Atoms Intensify Phonon Scattering Leading to High Thermoelectric Performance in SnTe.

SnTe is an intriguing alternative to PbTe for midtemperature thermoelectric applications. Despite steady progress, its performance is lagging, in part because of the large energy difference(Δ) between the light (L-band) and heavy (Σ-band) valence bands and higher lattice thermal conductivity (κ). Previous studies have shown that applying pressure can enhance the Seebeck coefficient () and power factor () of SnTe.

Anomalous Behavior in Dark-Bright Splitting Impacts the Biexciton Binding Energy in (BA)(MA)PbBr ( = 1-3).

Two-dimensional Ruddlesden-Popper series are an excellent system for tuning physical properties of the perovskite by controlling the layer number (). For instance, bandgap and exciton binding energies of the series gradually increase upon reducing via enhanced quantum and dielectric confinements. Here, we present findings that challenge the anticipated trend in electron-hole exchange interaction within (BA)MAPbBr ( = 1-3), which causes spin-dependent exciton level splitting into bright and dark states, where the latter is partially visible near the surface of the Br-based two-dimensional Ruddlesden-Popper series.

Tunable Anomalous Hall Effect in a Kagomé Ferromagnetic Weyl Semimetal.

Emerging from the intricate interplay of topology and magnetism, the giant anomalous Hall effect (AHE) is the most known topological property of the recently discovered kagomé ferromagnetic Weyl semimetal CoSnS with the magnetic Co atoms arranged on a kagomé lattice. Here it is reported that the AHE in CoSnS can be fine-tuned by an applied magnetic field orientated within ≈2° of the kagomé plane, while beyond this regime, it stays unchanged. Particularly, it can vanish in magnetic fields parallel to the kagomé plane and even decrease in magnetic fields collinear with the spin direction.

Molecular Origins of Near-Infrared Luminescence in Molybdenum and Tungsten Oxyhalide Perovskites.

Materials with near-infrared (near-IR) luminescence are desirable for applications in communications and sensing, as well as biomedical diagnostics and imaging. The most used inorganic near-IR emitters rely on precise doping of host crystal structures with select rare-earth or transition metal ions. Recently, another class of materials with intrinsic near-IR emission has been reported.

Vapor Growth of All-Inorganic 2D Ruddlesden-Popper Lead- and Tin-Based Perovskites.

The 2D Ruddlesden-Popper (RP) perovskites CsPbICl (Pb-based, = 1) and CsSnICl (Sn-based, = 1) stand out as unique and rare instances of entirely inorganic constituents within the more expansive category of organic/inorganic 2D perovskites. These materials have recently garnered significant attention for their strong UV-light responsiveness, exceptional thermal stability, and theoretically predicted ultrahigh carrier mobility. In this study, we synthesized Pb and Sn-based = 1 2D RP perovskite films covering millimeter-scale areas for the first time, utilizing a one-step chemical vapor deposition (CVD) method under atmospheric conditions.

Pressure induced structural and electronic band transition in CsPbBr.

Cesium lead bromide (CsPbBr) is a prominent halide perovskite with extensive optoelectronic applications. In this study, we report the pressure modulation of CsPbBr's crystal structure and electronic properties at room temperature up to 5 GPa. We have observed a crystal structure transition from the orthorhombic Pnma space group to a new monoclinic phase in the space group P2/c at 2.

In Situ Local Imaging of Ferromagnetism and Superconductivity in RbEuFeAs.

The coexistence of superconductivity and ferromagnetism is an intrinsically interesting research focus in condensed matter physics, but the study is limited by low superconducting () and magnetic () transition temperatures in related materials. Here, we used a scanning superconducting quantum interference device to image the in situ diamagnetic and ferromagnetic responses of RbEuFeAs with high and . We observed significant suppression of the superfluid density in the vicinity of the magnetic phase transition, signifying fluctuation-enhanced magnetic scatterings between Eu spins and Fe 3d conduction electrons.

Two-dimensional perovskitoids enhance stability in perovskite solar cells.

Two-dimensional (2D) and three-dimensional (3D) perovskite heterostructures have played a key role in advancing the performance of perovskite solar cells. However, the migration of cations between 2D and 3D layers results in the disruption of octahedral networks, leading to degradation in performance over time. We hypothesized that perovskitoids, with robust organic-inorganic networks enabled by edge- and face-sharing, could impede ion migration.

Two-dimensional perovskite templates for durable, efficient formamidinium perovskite solar cells.

We present a design strategy for fabricating ultrastable phase-pure films of formamidinium lead iodide (FAPbI) by lattice templating using specific two-dimensional (2D) perovskites with FA as the cage cation. When a pure FAPbI precursor solution is brought in contact with the 2D perovskite, the black phase forms preferentially at 100°C, much lower than the standard FAPbI annealing temperature of 150°C. X-ray diffraction and optical spectroscopy suggest that the resulting FAPbI film compresses slightly to acquire the (011) interplanar distances of the 2D perovskite seed.

Noncollinear Electric Dipoles in a Polar Chiral Phase of CsSnBr Perovskite.

Polar and chiral crystal symmetries confer a variety of potentially useful functionalities upon solids by coupling otherwise noninteracting mechanical, electronic, optical, and magnetic degrees of freedom. We describe two phases of the 3D perovskite, CsSnBr, which emerge below 85 K due to the formation of Sn(II) lone pairs and their interaction with extant octahedral tilts. Phase II (77 K < < 85 K, space group 2/) exhibits ferroaxial order driven by a noncollinear pattern of lone pair-driven distortions within the plane normal to the unique octahedral tilt axis, preserving the inversion symmetry observed at higher temperatures.

Structural Evolution and Photoluminescence Quenching across the FASnIBr ( = 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 FASnIBr ( = 0-3) family of compounds provides the first example where the assumption breaks down, as the composition space is broken into two unique regimes ( = 0-2.

Implications and Optimization of Domain Structures in IV-VI High-Entropy Thermoelectric Materials.

High-entropy semiconductors are now an important class of materials widely investigated for thermoelectric applications. Understanding the impact of chemical and structural heterogeneity on transport properties in these compositionally complex systems is essential for thermoelectric design. In this work, we uncover the polar domain structures in the high-entropy PbGeSnSeTe system and assess their impact on thermoelectric properties.

Ultrafast Photoinduced Phase Change in SnSe.

Time-resolved multiterahertz (THz) spectroscopy is used to observe an ultrafast, nonthermal electronic phase change in SnSe driven by interband photoexcitation with 1.55 eV pump photons. The transient THz photoconductivity spectrum is found to be Lorentzian-like, indicating charge localization and phase segregation.

Improved charge extraction in inverted perovskite solar cells with dual-site-binding ligands.

Inverted (pin) perovskite solar cells (PSCs) afford improved operating stability in comparison to their nip counterparts but have lagged in power conversion efficiency (PCE). The energetic losses responsible for this PCE deficit in pin PSCs occur primarily at the interfaces between the perovskite and the charge-transport layers. Additive and surface treatments that use passivating ligands usually bind to a single active binding site: This dense packing of electrically resistive passivants perpendicular to the surface may limit the fill factor in pin PSCs.

Nanotube Structure of AsPSSe ( = 0, 1).

Single-wall nanotubes of isostructural AsPSSe ( = 0, 1) are grown from solid-state reaction of stoichiometric amounts of the elements. The structure of AsPS was determined using single-crystal X-ray diffraction and refined in space group . The infinite, single-walled AsPS nanotubes have an outer diameter of ≈1.

Asymmetric Triphenylethylene-Based Hole Transporting Materials for Highly Efficient Perovskite Solar Cells.

Molecular hole-transporting materials (HTMs) having triphenylethylene central core were designed, synthesized, and employed in perovskite solar cell (PSC) devices. The synthesized HTM derivatives were obtained in a two- or three-step synthetic procedure, and their characteristics were analyzed by various thermoanalytical, optical, photophysical, and photovoltaic techniques. The most efficient PSC device recorded a 23.

Ligand Desorption and Fragmentation in Oleate-Capped CdSe Nanocrystals under High-Intensity Photoexcitation.

Semiconductor nanocrystals (NCs) offer prospective use as active optical elements in photovoltaics, light-emitting diodes, lasers, and photocatalysts due to their tunable optical absorption and emission properties, high stability, and scalable solution processing, as well as compatibility with additive manufacturing routes. Over the course of experiments, during device fabrication, or while in use commercially, these materials are often subjected to intense or prolonged electronic excitation and high carrier densities. The influence of such conditions on ligand integrity and binding remains underexplored.

Raman Shifts in Two-Dimensional van der Waals Magnets Reveal Magnetic Texture Evolution.

Two-dimensional (2D) van der Waals magnets comprise rich physics that can be exploited for spintronic applications. We investigate the interplay between spin-phonon coupling and spin textures in a 2D van der Waals magnet by combining magneto-Raman spectroscopy with cryogenic Lorentz transmission electron microscopy. We find that when stable skyrmion bubbles are formed in the 2D magnet, a field-dependent Raman shift can be observed, and this shift is absent for the 2D magnet prepared in its ferromagnetic state.

Solution-processable mixed-anion cluster chalcohalide RbReSI in a light-emitting diode.

Rhenium chalcohalide cluster compounds are a photoluminescent family of mixed-anion chalcohalide cluster materials. Here we report the new material RbReSI, which crystallizes in the cubic space group Fm[Formula: see text]m and contains isolated [ReSI] clusters. RbReSI has a band gap of 2.