Determinants of regioselectivity of heterostructures in cation exchange reactions.

A cation exchange (CE) reaction offers a remarkable opportunity to create versatile metal sulfide nanocrystals (NCs) with arbitrary complexity in composition, structure, and functionality. The concept of regioselectivity has been discovered and developed to build the target heterostructures through CE reactions, yet a general principle of regioselectivity remains unclear. In this work, we establish connections between experimental results and theoretical insights to elucidate the determinants of regioselectivity using designed aliovalent CE reactions on a two-dimensional template.

Unusual defect properties of the one-dimensional photovoltaic semiconductor selenium.

Defect tolerance is crucial in photovoltaic absorbers. Here we report that trigonal selenium (t-Se) exhibits a perovskite-like antibonding valence band maximum arising from Se p-p coupling. This results in the shallow nature of dominant Se vacancy defects.

Lanthanide-Like Contraction Enables the Fabrication of High-Purity Selenium Films for Efficient Indoor Photovoltaics.

The lanthanide contraction involves a reduction in atomic radius among f-block elements below the expected level. A similar contraction is observed in group-16 elements. The atomic radius of Se (117 pm) is slightly larger than that of S (104 pm) arising from the presence of d electrons, compared to the significant increase in atomic radius from O (73 pm) to S.

Template Selection Strategy for Synthesis of One-Dimensional CrSbSe Ferromagnetic Semiconductor Nanoribbons.

CrSbSe─the only experimentally validated one-dimensional (1D) ferromagnetic semiconductor─has recently attracted significant attention. However, all reported synthesis methods for CrSbSe nanocrystals are based on top-down methods. Here we report a template selection strategy for the bottom-up synthesis of CrSbSe nanoribbons.

Adhesion-Controlled Heterogeneous Nucleation of Tin Halide Perovskites for Eco-Friendly Indoor Photovoltaics.

The rapid development of the Internet of Things (IoT) has accelerated the advancement of indoor photovoltaics (IPVs) that directly power wireless IoT devices. The interest in lead-free perovskites for IPVs stems from their similar optoelectronic properties to high-performance lead halide perovskites, but without concerns about toxic lead leakage in indoor environments. However, currently prevalent lead-free perovskite IPVs, especially tin halide perovskites (THPs), still exhibit inferior performance, arising from their uncontrollable crystallization.

Sustainable Recycling of Selenium-Based Optoelectronic Devices.

Selenium (Se), the world's oldest optoelectronic material, has been widely applied in various optoelectronic devices such as commercial X-ray flat-panel detectors and photovoltaics. However, despite the rare and widely-dispersed nature of Se element, a sustainable recycling of Se and other valuable materials from spent Se-based devices has not been developed so far. Here a sustainable strategy is reported that makes use of the significantly higher vapor pressure of volatile Se compared to other functional layers to recycle all of them from end-of-life Se-based devices through a closed-space evaporation process, utilizing Se photovoltaic devices as a case study.

Structure of Amorphous Selenium: Small Ring, Big Controversy.

Selenium (Se) discovered in 1817 belongs to the family of chalcogens. Surprisingly, despite the long history of over two centuries and the chemical simplicity of Se, the structure of amorphous Se (a-Se) remains controversial to date regarding the dominance of chains versus rings. Here, we find that vapor-deposited a-Se is composed of disordered rings rather than chains in melt-quenched a-Se.

Te Se Photodiode Shortwave Infrared Detection and Imaging.

Short-wave infrared detectors are increasingly important in the fields of autonomous driving, food safety, disease diagnosis, and scientific research. However, mature short-wave infrared cameras such as InGaAs have the disadvantage of complex heterogeneous integration with complementary metal-oxide-semiconductor (CMOS) readout circuits, leading to high cost and low imaging resolution. Herein, a low-cost, high-performance, and high-stability Te Se short-wave infrared photodiode detector is reported.

Regioselective Multisite Atomic-Chlorine Passivation Enables Efficient and Stable Perovskite Solar Cells.

Passivating defects using organic halide salts, especially chlorides, is an effective method to improve power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) arising from the stronger Pb-Cl bonding than Pb-I and Pb-Br bonding. However, Cl anions with a small radius are prone to incorporation into the perovskite lattice that distorts the lead halide octahedron, degrading the photovoltaic performance. Here, we substitute atomic-Cl-containing organic molecules for widely used ionic-Cl salts, which not only retain the efficient passivation by Cl but also prevent the incorporation of Cl into the bulk lattice, benefiting from the strong covalent bonding between Cl atoms and organic frameworks.

Indoor photovoltaics awaken the world's first solar cells.

Selenium (Se) solar cells were the world's first solid-state photovoltaics reported in 1883, opening the modern photovoltaics. However, its wide bandgap (~1.9 eV) limits sunlight harvesting.

Mitigating Electron Leakage of Solid Electrolyte Interface for Stable Sodium-Ion Batteries.

The interfacial stability is highly responsible for the longevity and safety of sodium ion batteries (SIBs). However, the continuous solid-electrolyte interphase(SEI) growth would deteriorate its stability. Essentially, the SEI growth is associated with the electron leakage behavior, yet few efforts have tried to suppress the SEI growth, from the perspective of mitigating electron leakage.

Solution-processed Ge(ii)-based chalcogenide thin films with tunable bandgaps for photovoltaics.

Solution processes have been widely used to construct chalcogenide-based thin-film optoelectronic and electronic devices that combine high performance with low-cost manufacturing. However, Ge(ii)-based chalcogenide thin films possessing great potential for optoelectronic devices have not been reported using solution-based processes; this is mainly attributed to the easy oxidation of intermediate Ge(ii) to Ge(iv) in the precursor solution. Here we report solution-processed deposition of Ge(ii)-based chalcogenide thin films in the case of GeSe and GeS films by introducing hypophosphorous acid as a suitable reducing agent and strong acid.

Robust Self-Assembled Molecular Passivation for High-Performance Perovskite Solar Cells.

Defect passivation via post-treatment of perovskite films is an effective method to fabricate high-performance perovskite solar cells (PSCs). However, the passivation durability is still an issue due to the weak and vulnerable bonding between passivating functional groups and perovskite defect sites. Here we propose a cholesterol derivative self-assembly strategy to construct crosslinked and compact membranes throughout perovskite films.

Strain in perovskite solar cells: origins, impacts and regulation.

Metal halide perovskite solar cells (PSCs) have seen an extremely rapid rise in power conversion efficiencies in the past few years. However, the commercialization of this class of emerging materials still faces serious challenges, one of which is the instability against external stimuli such as moisture, heat and irradiation. Much focus has deservedly been placed on understanding the different origins of intrinsic instability and thereby enhancing their stability.

Investigation of the sublimation mechanism of GeSe and GeS.

GeSe and GeS have emerged as promising light-harvesting materials for photovoltaics due to their attractive optoelectronic properties, non-toxic and earth-abundant constituents, and excellent stability. Here we unveil the diatomic molecule sublimation mechanism of GeSe and GeS that directly guides the optimization of GeSe and GeS solar-cell fabricated the close-space sublimation method.

Surface-Defect States in Photovoltaic Absorber GeSe.

GeSe is an emerging promising light-harvesting material for photovoltaics due to its excellent optoelectronic properties, nontoxic and earth-abundant constituents, and high stability. In particular, perovskite-like antibonding states at the valence band maximum arising from Ge-4s and Se-4p coupling enable the bulk-defect-tolerant properties in GeSe. However, a fundamental understanding of surface-defect states in GeSe, another important factor for high-performance photovoltaics, is still lacking.

One-Pot Synthesis Enables Magnetic Coupled CrTe/MnTe/CrTe Integrated Heterojunction Nanorods.

Magnetic heterostructures offer great promise in spintronic devices due to their unique magnetic properties, such as exchange bias effect, topological superconductivity, and magneto-resistance. Although various magnetic heterostructures including core/shell, multilayer, and van der Waals systems have been fabricated recently, the construction of perfect heterointerfaces usually rely on complicated and high-cost fabrication methods such as molecular-beam epitaxy; surprisingly, few one-dimensional (1D) bimagnetic heterojunctions, which provide multidegrees of freedom to modulate magnetic properties via magnetic anisotropy and interface coupling, have been fabricated to date. Here we report a one-pot solution-based method for the synthesis of ferromagnetic/antiferromagnetic/ferromagnetic heterojunction nanorods with excellent heterointerfaces in the case of CrTe/MnTe/CrTe.

Interfacial Strain Engineering in Wide-Bandgap GeS Thin Films for Photovoltaics.

Wide-bandgap semiconductors exhibiting a bandgap of ∼1.7-1.9 eV have generated great interest recently due to their important applications in tandem solar cells as top cells and emerging indoor photovoltaics.

An antibonding valence band maximum enables defect-tolerant and stable GeSe photovoltaics.

In lead-halide perovskites, antibonding states at the valence band maximum (VBM)-the result of Pb 6s-I 5p coupling-enable defect-tolerant properties; however, questions surrounding stability, and a reliance on lead, remain challenges for perovskite solar cells. Here, we report that binary GeSe has a perovskite-like antibonding VBM arising from Ge 4s-Se 4p coupling; and that it exhibits similarly shallow bulk defects combined with high stability. We find that the deep defect density in bulk GeSe is ~10 cm.

In-plane anisotropic 2D Ge-based binary materials for optoelectronic applications.

In-plane anisotropic two-dimensional (2D) materials possess unique in-plane anisotropic physical properties arising from their low crystal lattice symmetry. Among these low-symmetry 2D materials, anisotropic Ge-based binary materials have the advantages of simple binary and earth-abundant compositions, good stability, highly anisotropic physical properties along two principle axes, and wide coverage of bandgaps, enabling use in broadband photodetection from the infrared to ultraviolet region. Here, we review recent progress in in-plane anisotropic 2D Ge-based binary materials, focusing on their anisotropic structural, electrical and optical properties.

Crystallization Kinetics Modulation of FASnI Films with Pre-nucleation Clusters for Efficient Lead-Free Perovskite Solar Cells.

Tin halide perovskites are rising as promising materials for lead-free perovskite solar cells (PSCs). However, the crystallization rate of tin halide perovskites is much faster than the lead-based analogs, leading to more rampant trap states and lower efficiency. Here, we disclose a key finding to modulate the crystallization kinetics of FASnI through a non-classical nucleation mechanism based on pre-nucleation clusters (PNCs).

Regulating strain in perovskite thin films through charge-transport layers.

Thermally-induced tensile strain that remains in perovskite films following annealing results in increased ion migration and is a known factor in the instability of these materials. Previously-reported strain regulation methods for perovskite solar cells (PSCs) have utilized substrates with high thermal expansion coefficients that limits the processing temperature of perovskites and compromises power conversion efficiency. Here we compensate residual tensile strain by introducing an external compressive strain from the hole-transport layer.