Search

The unique intermolecular van der Waals force in emerging two-dimensional inorganic molecular crystals (2DIMCs) endows them with highly tunable structures and properties upon applying external stimuli. Using high pressure to modulate the intermolecular bonding, here we reveal the highly tunable charge transport behavior in 2DIMCs for the first time, from an insulator to a semiconductor. As pressure increases, 2D α-Sb2O3 molecular crystal undergoes three isostructural transitions, and the intermolecular bonding enhances gradually, which results in a considerably decreased bandgap by 25% and a greatly enhanced charge transport. Impressively, the in-situ resistivity measurement of the α-Sb2O3 flake shows a sharp drop by 5 orders of magnitude in 0 - 3.2 GPa. This work sheds new light on the manipulation of charge transport in 2DIMCs and is of great significance for promoting the fundamental understanding and potential applications of 2DIMCs in advanced modern technologies.

Two-dimensional (2D) semiconductor heterostructures are key building blocks for many electronic and optoelectronic devices. Reconfiguring the band-edge states and modulating their interplay with charge carriers at the interface in a continuous manner have long been sought yet are challenging. Here, using organic semiconductor–incorporated 2D halide perovskites as the model system, we realize the manipulation of band-edge states and charge distribution via mechanical—rather than chemical or thermal—regulation. Compression induces band-alignment switching and charge redistribution due to the different pressure responses of organic and inorganic building blocks, giving controllable emission properties of 2D perovskites. We propose and demonstrate a “pressure gating” strategy that enables the control of multiple emission states within a single material. We also reveal that band-alignment transition at the organic-inorganic interface is intrinsically not well resolved at room temperature owing to the thermally activated transfer and shuffling of band-edge carriers. This work provides important fundamental insights into the energetics and carrier dynamics of hybrid semiconductor heterostructures.

Freestanding metallic nanosheets (or 2D metals) have been attracting tremendous research interest because of their potential applications in numerous important fields, such as green energy, biomedi...

Understanding the relationships between the local structures and physical properties of low-dimensional ferroelectrics is of both fundamental and practical importance. Here, pressure-induced enhancement in the photocurrent of SbSI is observed by using pressure to regulate the lone-pair electrons (LPEs). The reconfiguration of LPEs under pressure leads to the inversion symmetry broken in the crystal structure and an optimum bandgap according to the Shockley–Queisser limit. The increased polarization caused by the stereochemical expression of LPEs results in a significantly enhanced photocurrent at 14 GPa. Our research enriches the foundational understanding of structure–property relationships by regulating the stereochemical role of LPEs and offers a distinctive approach to the design of ferroelectric-photovoltaic materials.

Pressure processing is efficient to regulate the structural and physical properties of two-dimensional (2D) halide perovskites which have been emerging for advanced photovoltaic and light-emitting applications. Increasing numbers of studies have reported pressure-induced and/or enhanced emission properties in the 2D halide perovskites. However, no research has focused on their photoresponse properties under pressure tuning. It is also unclear how structural change affects their excitonic features, which govern the optoelectronic properties of the halide perovskites. Herein, we report significantly enhanced photocurrents in the all-inorganic 2D perovskite Cs2PbI2Cl2, achieving over 3 orders of magnitude increase at the industrially achievable level of 2 GPa in comparison with its initial photocurrent. Lattice compression effectively regulates the excitonic features of Cs2PbI2Cl2, reducing the exciton binding energy considerably from 133 meV at ambient conditions to 78 meV at 2.1 GPa. Impressively, such a reduced exciton binding energy of 2D Cs2PbI2Cl2 is comparable to the values of typical 3D perovskites (MAPbBr3 and MAPbI3), facilitating the dissociating of excitons into free carriers and enhancing the photocurrent. Further pressurization leads to a layer-sliding-induced phase transition and an anomalous negative linear compression, which has not been observed so far in other halide perovskites. Our findings reveal the dramatically enhanced photocurrents in the 2D halide perovskite by regulating its excitonic features and, more broadly, provide new insights into materials design toward extraordinary properties.

Lone-pair electrons (LPEs) ns2 in subvalent 14 and 15 groups lead to highly anharmonic lattice and strong distortion polarization, which are responsible for the groups' outstanding thermoelectric and optoelectronic properties. However, their dynamic stereochemical role in structural and physical properties is still unclear. Here, by introducing pressure to tune the behavior of LPEs, we systematically investigate the lone-pair stereochemical role in a Bi2O2S. The gradually suppressed LPEs during compression show a nonlinear repulsive electrostatic force, resulting in two anisotropic structural transitions. An orthorhombic-to-tetragonal phase transition happens at 6.4 GPa, caused by the dynamic cation centering. This structural transformation effectively modulates the optoelectronic properties. Further compression beyond 13.2 GPa induces a 2D-to-3D structural transition due to the disappearance of the Bi-6s2 LPEs. Therefore, the pressure-induced LPE reconfiguration dominates these anomalous variations of lattice, electronic, and optical properties. Our findings provide new insights into the materials optimization by regulating the characters of LPEs.

Low-dimensional perovskite-related metal halides have emerged as a new class of light-emitting materials with tunable broadband emission from self-trapped excitons (STEs). Although various types of low-dimensional structures have been developed, fundamental understating of the structure-property relationships for this class of materials is still very limited, and further improvement of their optical properties remains greatly important. Here, we report a significant pressure-induced photoluminescence (PL) enhancement in a one-dimensional hybrid metal halide C4N2H14PbBr4, and the underlying mechanisms are investigated using in situ experimental characterization and first-principles calculations. Under a gigapascal pressure scale, the PL quantum yields (PLQYs) were quantitatively determined to show a dramatic increase from the initial value of 20% at ambient conditions to over 90% at 2.8 GPa. With in situ characterization of photophysical properties and theoretical analysis, we found that the PLQY enhancement was mainly attributed to the greatly suppressed nonradiative decay. Pressure can effectively tune the energy level of self-trapped states and increase the exciton binding energy, which leads to a larger Stokes shift. The resulting highly localized excitons with stronger binding reduce the probability for carrier scattering, to result in the significantly suppressed nonradiative decay. Our findings clearly show that the characteristics of STEs in low-dimensional metal halides can be well-tuned by external pressure, and enhanced optical properties can be achieved.

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)2 (GA)Pb2 I7 (HA=n-hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non-luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above-band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two-fold higher PL emission compared with the pristine (HA)2 (GA)Pb2 I7 .

Molecular crystals of dicoronylene (C48H20), a member of very large polycyclic aromatic hydrocarbons (PAHs), exhibits strong red fluorescence under ambient conditions. This strong fluorescence induced by visible light excitation obscures entire Raman spectrum of dicoronylene. We employed in-situ high-pressure photoluminescence spectroscopy to observe a reversible piezochromic effect, in which the fluorescence exhibits a drastic red-shift with a rapid quenching of intensity. Above 4 GPa, under red-shifted and reduced fluorescence, hidden Raman modes are observed with 532 nm green laser up to 20 GPa. In this work, we show that the application of pressure can finely tune the fluorescence of dicoronylene, allowing the observation of the Raman spectrum with an appropriate laser wavelength and we discovered that dicoronylene has high chemical stability among PAH molecules with multiple aromatic rings.

Solids can be generally categorized by their structures into crystalline and amorphous states with different interactions among atoms dictating their properties. Crystalline-amorphous hybrid structures, combining the advantages of both ordered and disordered components, present a promising opportunity to design materials with emergent collective properties. Hybridization of crystalline and amorphous structures at the sublattice level with long-range periodicity has been rarely observed. Here, we report a nested order-disorder framework (NOF) constructed by a crystalline matrix with self-filled amorphous-like innards that is obtained by using pressure to regulate the bonding hierarchy of Cu12Sb4S13. Combined in situ experimental and computational methods demonstrate the formation of disordered Cu sublattice which is embedded in the retained crystalline Cu framework. Such a NOF structure gives a low thermal conductivity (~0.24 W·m−1·K−1) and a metallic electrical conductivity (8 × 10−6 Ω·m), realizing the collaborative improvement of two competing physical properties. These findings demonstrate a category of solid-state materials to link the crystalline and amorphous forms in the sublattice-scale, which will exhibit extraordinary properties.

Developing safe, efficient and environment-friendly energy storage systems continues to inspire researchers to synthesize new electrode materials. Doping or substituting host material by some guest elements has been regarded as an effective way to improve the performance of supercapacitors. In this work, single-phase CuCo2−xNixS4 materials were synthesized by a facile two-step hydrothermal method, where Co in CuCo2S4 was substituted by Ni. Cobalt could be easily substituted with Ni in a rational range to keep its constant phase. But, a high content of Ni resulted in a multi-phase composite. Among a series of CuCo2−xNixS4 materials with different Ni/Co mole ratios, CuCo1.25Ni0.75S4 material presented a significantly high specific capacitance (647 F g−1 or 272 C g−1 at 1 A g−1) and the best cycling stability (∼98% specific capacitance retention after 10,000 charge-discharge cycles), which was mainly due to the modified composition, specific single phase, higher electroconductivity, more electroactive sites and the synergistic effect between Ni and Co. Moreover, the assembled asymmetric capacitor using CuCo1.25Ni0.75S4 as a positive electrode and activated carbon as a negative electrode delivered a high energy density of 31.8 Wh kg−1 at the power density of 412.5 W kg−1. These results demonstrated that ternary metal sulfides of CuCo2−xNixS4 are promising electrode materials for high-performance supercapacitors.

A series of mixed metal sulfides of NixCu1−xCo2S4 were synthesized by a facile two-step hydrothermal method and they were investigated as electrode materials for supercapacitor. A substitutional solid solution can be easily formed due to the same atom occupation and similar crystal radius of Ni and Cu in the metal sulfides. The electrochemical performances of the mixed metal sulfides are strongly influenced by the chemical compositions, though they have the same crystal structure. Among all the as-prepared materials, Ni0.67Cu0.33Co2S4 shows the best electrochemical performances with the highest specific capacitance of 1340.48 F g−1 at 1 A g−1, outstanding rate capability and excellent cycling stability. The improved performances can be attributed to the high crystallinity, modified microstructure, increased electrochemical sites and improved electroconductivity caused by lattice distortion as well as the synergistic effect in the Cu-substituted NiCo2S4. Furthermore, the assembled two-electrode hybrid device Ni0.67Cu0.33Co2S4//activated carbon can deliver a high energy density of 40 Wh kg−1 at the power density of 412.5 W kg−1, showing a great potential for energy storage.

Low‐dimensional hybrid metal halides are emerging as a highly promising class of single‐component white‐emitting materials for their unique broadband emission from self‐trapped excitons (STEs). Despite substantial progress in the development of these metal halides, many challenges remain to be addressed to obtain a better fundamental understanding of the structure–property relationship and realize the full potentials of this class of materials. Here, via pressure regulation, a near 100% photoluminescence quantum yield (PLQY) of broadband emission is achieved in a corrugated 1D hybrid metal halide C5N2H16Pb2Br6, which possesses a highly distorted structure with an initial PLQY of 10%. Compression reduces the overlap between STE states and ground state, leading to a suppressed phonon‐assisted non‐radiative decay. The PL evolution is systematically demonstrated to be controlled by the pressure‐regulated exciton–phonon coupling which can be quantified using Huang–Rhys factor S. Detailed studies of the S‐PLQY relation for a series of 1D hybrid metal halides (C5N2H16Pb2Br6, C4N2H14PbBr4, C6N2H16PbBr4, and (C6N2H16)3Pb2Br10) reveal a quantitative structure–property relationship that regulating S factor toward 28 leads to the maximum emission., This work demonstrates a quantitative relationship between photoluminescence quantum yield (PLQY) and exciton–phonon coupling in a series of 1D hybrid metal halides. Using pressure to regulate the exciton–phonon interaction, a near 100% PLQY of broadband emission from self‐trapped excitons is achieved in a corrugated 1D compound C5N2H16Pb2Br6 whose initial PLQY is 10%.

Pressure processing is efficient to regulate the structural and physical properties of two-dimensional (2D) halide perovskites which have been emerging for advanced photovoltaic and light-emitting applications. Increasing numbers of studies have reported pressure-induced and/or enhanced emission properties in the 2D halide perovskites. However, no research has focused on their photoresponse properties under pressure tuning. It is also unclear how structural change affects their excitonic features, which govern the optoelectronic properties of the halide perovskites. Herein, we report significantly enhanced photocurrents in the all-inorganic 2D perovskite Cs

Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH3NH3GeI3, HC(NH2)2GeI3, and CsGeI3]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH3NH3+ with Cs+ to control the distortion in (CH3NH3)1-xCsxGeI3, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI3 further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods., By regulating the highly distorted halide perovskites using pressure, a quantitative relationship between structural distortion and emission property is demonstrated. The extracted principle is applied to materials design and the results give further support to the revealed relationship.

Low-dimensional perovskite-related metal halides have emerged as a new class of light-emitting materials with tunable broadband emission from self-trapped excitons (STEs). Although various types of low-dimensional structures have been developed, fundamental understating of the structure-property relationships for this class of materials is still very limited, and further improvement of their optical properties remains greatly important. Here, we report a significant pressure-induced photoluminescence (PL) enhancement in a one-dimensional hybrid metal halide C

Control of structural ordering in noble metals is very important for the exploration of their properties and applications, and thus it is highly desired to have an in-depth understanding of their structural transitions. Herein, through high-pressure treatment, the mutual transformations between crystalline and amorphous phases are achieved in Pd nanosheets (NSs) and nanoparticles (NPs). The amorphous domains in the amorphous/crystalline Pd NSs exhibit pressure-induced crystallization (PIC) phenomenon, which is considered as the preferred structural response of amorphous Pd under high pressure. On the contrary, in the spherical crystalline@amorphous core-shell Pd NPs, pressure-induced amorphization (PIA) is observed in the crystalline core, in which the amorphous-crystalline phase boundary acts as the initiation site for the collapse of crystalline structure. The distinct PIC and PIA phenomena in two different heterophase Pd nanostructures might originate from the different characteristics of Pd NSs and NPs, including morphology, amorphous-crystalline interface, and lattice parameter. This work not only provides insights into the phase transition mechanisms of amorphous/crystalline heterophase noble metal nanostructures, but also offers an alternative route for engineering noble metals with different phases.

Prussian blue analogues (PBA) recently have received great interest for promising applications in low-cost sodium-ion batteries (SIBs). However, controlled synthesis of high-performance PBA is still challenging. In this work, a facile precipitation route was used to synthesize Na-rich PBAs with superior electrochemical performance. It was found that two shapes of the products, namely, small irregular particles and large cuboid particles, coexist by adding sodium citrate in the sodium hexacyanoferrate side during the synthesis. The product shows large capacity (144 mAh g–1 under a 0.1 C rate), good rate performance (115.6 mAh g–1 under a 1 C rate, 86.6 mAh g–1 under a 10 C rate), and long-term cycling stability (73.4% retention after 780 cycles under a 0.5 C rate, 72.7% retention after 2100 cycles under a 1 C rate). This work offers a promising route to prepare PBA-based cathode materials for high-performance SIBs.

Low crystalline CoSx was fabricated by anion-exchange of 2-dimensional (2D) cobalt carbonate hydroxide (CoCH) using aqueous sodium sulfide solution at room temperature. It was proved that single crystalline CoCH nanoplates would transform into porous 2D CoSx with low crystallinity after the anion-exchange. When they were used as electrode materials for supercapacitor, the 2D CoSx material had a much higher specific capacitance than its precursor due to their different compositions and electroconductivities. CoSx had a high specific capacitance of 863 F g−1 at 1 A g−1 and a good stability during long time charge-discharge processes, about 64.7% of initial capacitance retention after 10000 cycles. Asymmetric hybrid devices using 2D CoSx as positive electrode and activated carbon as negative electrode were assembled, and the capacitor devices were able to achieve a high energy density of 33.56 Wh kg−1 at the power density of 400 W kg−1. The high performances of the porous CoSx make it a promising electrode material for energy storage.

In this work, hierarchical NiCo2O4@Co-Fe layered double hydroxide (LDH) core-shell nanowire arrays on Ni foam were synthesized by facile hydrothermal and calcination methods. The pre-formed NiCo2O4 nanowires on Ni foam acted as a substrate and then guided the deposition of Co-Fe LDH nanoflakes on their surface to form a highly porous hierarchical core–shell heterostructure. Meanwhile, NiCo2O4 nanowires and Co-Fe LDH nanoflake films were also deposited on Ni foam. The materials were well characterized and used for electrochemical energy storage. The unique core-shell configuration of NiCo2O4@Co-Fe LDH can make full use of the synergistic effects of two components, provide sufficient electroactive sites as well as facilitate the charge transportation process. The as-prepared NiCo2O4@Co-Fe LDH nanowire arrays displayed outstanding electrochemical performances with a high specific capacitance of 1557.5 F g−1 at 1 A g−1. The assembled two-electrode hybrid device NiCo2O4@Co-Fe LDH//activated carbon could deliver an energy density of 28.94 Wh kg−1 at the power density of 950 W kg−1, showing a promising potential in energy storage and conversion.

Amorphous and crystalline copper cobalt sulfides are successfully synthesized via a hydrothermal method at different temperatures and researched as electrode materials for supercapacitor. The reaction mechanisms during the sulfidation and hydrothermal processes are investigated and clarified. It is demonstrated that the hydrothermal temperature is a crucial factor for the crystallinity, morphology and electrochemical performance of CuCo2S4. Among all the samples, the CuCo2S4 synthesized at 150 °C shows the highest specific capacitance of 515 F g-1 at 1 A g−1 as well as good cycling stability with ∼93.3% capacitance retention after 10000 cycles at 5 A g−1. An asymmetric device which is assembled by using optimized CuCo2S4 electrode as positive electrode and activated carbon as negative electrode material is able to deliver an ultrahigh energy density of 50.56 Wh kg−1 at a power density of 4.6 kW kg−1, and remains 20.93 Wh kg−1 at a high power density of 22.5 kW kg−1, with ∼99% capacity retention after 10000 cycles. Based on the results above, the CuCo2S4 materials prepared by our method possess a considerable potential as electrode materials for supercapacitor applications.

Zero-dimensional (0D) hybrid metal halides are under intensive investigation owing to their unique physical properties, such as the broadband emission from highly localized excitons that is promising for white-emitting lighting. However, fundamental understanding of emission variations and structure–property relationships is still limited. Here, by using pressure processing, we obtain robust exciton emission in 0D (C9NH20)6Pb3Br12 at room temperature that can survive to 80 GPa, the recorded highest value among all the hybrid metal halides. In situ experimental characterization and first-principles calculations reveal that the pressure-induced emission is mainly caused by the largely suppressed phonon-assisted nonradiative pathway. Lattice compression leads to phonon hardening, which considerably weakens the exciton–phonon interaction and thus enhances the emission. The robust emission is attributed to the unique structure of separated spring-like [Pb3Br12]6− trimers, which leads to the outstanding stability of the optically active inorganic units. Our findings not only reveal abnormally robust emission in a 0D metal halide, but also provide new insight into the design and optimization of local structures of trimers and oligomers in low-dimensional hybrid materials.

The development of electrode materials with hierarchically porous structure and high electrochemical stability is crucial for the electric energy density of supercapacitors. Hollow microspheres of Ni-Co layered double hydroxides (LDHs) and Ni-Mn LDHs are fabricated with a simple co-precipitation method at low temperature using SiO2 microspheres as a sacrifice template. The as-fabricated two LDH hollow microspheres possess a unique 3D architecture and exhibit high specific capacitance, as well as excellent rate and cycling performances as electrode materials of supercapacitors. A specific capacitance of 1766.4 F g−1 at 1 A g−1 is achieved for Ni-Co LDHs electrode, much higher than that of Ni-Mn LDHs. A hybrid capacitor composed of Ni-Co LDHs hollow spheres and activated carbon is fabricated and evaluated for practical application, providing an energy density of 44.3 Wh kg−1 at a power density of 0.425 kW kg−1. This study indicates that the hollow LDH microsphere prepared by our method is a promising material for supercapacitors.

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)

Numerous exotic properties have been discovered in Dirac Semimetals (DSMs) and Weyl Semimetals (WSMs). In a given DSM/WSM, the Dirac/Weyl nodes usually coexist with other bulk states, making their respective contribution elusive. In this work, we distinguish the role of bulk states from the tilted Dirac nodes on the transport properties in DSMs. Specifically, we applied pressure to a type-II DSM material, PtTe2, and studied its pressure modified electronic and lattice structure systematically by using in situ transport measurements and X-ray diffraction (XRD). A pressure-induced transition at about 20 GPa is revealed in the transport properties, while the layered lattice structure is robust against pressure as illustrated in XRD measurement results. Density functional theory (DFT) calculations suggest that this is originated from the Lifshitz transition in the bulk states. Our findings provide evidence to identify the bulk states’ influence on transport from the topologically-protected DSM states in the DSM material.