Stable Intermediate Phase Research Articles

Collaborative Fabrication of High-Quality Perovskite Films for Efficient Solar Modules through Solvent Engineering and Vacuum Flash System.

The vacuum flash solution method has gained widespread recognition in the preparation of perovskite thin films, laying the foundation for the industrialization of perovskite solar cells. However, the low volatility of dimethyl sulfoxide and its weak interaction with formamidine-based perovskites significantly hinder the preparation of cell modules and the further improvement of photovoltaic performance. In this study, we describe an efficient and reproducible method for preparing large-scale, highly uniform formamidinium lead triiodide (FAPbI3) perovskite films. This is achieved by accelerating the vacuum flash rate and leveraging the complex synergism. Specifically, we designed a dual pump system to accelerate the depressurization rate of the vacuum system and compared the quality of perovskite film formed at different depressurization rates. Further, to overcome the limitations posed by DMSO, we substituted N-methylpyrrolidone as the ligand solvent, creating a stable intermediate complex phase. After annealing, it can be transformed into a uniform and pinhole-free FAPbI3 film. Due to the superior quality of these films, the large area perovskite solar module achieved a power conversion efficiency of 22.7% with an active area of 21.4 cm2. Additionally, it obtained an official certified efficiency of 22.1% with an aperture area of 22 cm2, and it demonstrated long-term stability.

Lead-Chelating Intermediate for Air-Processed Phase-Pure FAPbI3 Perovskite Solar Cells.

Formamidinium-lead triiodide (FAPbI3) perovskite holds promise as a prime candidate in the realm of perovskite photovoltaics. However, the photo-active α-FAPbI3 phase, existing as a metastable state, is observable solely at elevated temperatures and is susceptible to degradation into the δ-phase in ambient air. Therefore, the attainment of phase-stable α-FAPbI3 in ambient conditions has become a crucial objective in perovskite research. Here, we proposed an efficient conversion process of PbI2 into the α-FAPbI3 perovskites in ambient air. This conversion was facilitated by the introduction of chelating molecules, which interacted with PbI2 to form an intermediate phase. Due to the reduced formation barrier resulting from the altered reaction pathway, this stable intermediate phase transitioned directly into α-FAPbI3 upon the deposition of the organic cation solution, effectively bypassing the formation of δ-FAPbI3. Consequently, the ambient-fabricated FAPbI3 perovskite solar cells (PSCs) exhibited an outstanding power conversion efficiency of 25.08 %, along with a high open-circuit voltage of 1.19 V. Furthermore, the unencapsulated devices demonstrated remarkable environmental stability. Notably, this innovative approach promises broad applicability across various chelating molecules, opening new avenues for further progress in the ambient air fabrication of FAPbI3 PSCs.

Lead‐Chelating Intermediate for Air‐Processed Phase‐Pure FAPbI3 Perovskite Solar Cells

AbstractFormamidinium‐lead triiodide (FAPbI3) perovskite holds promise as a prime candidate in the realm of perovskite photovoltaics. However, the photo‐active α‐FAPbI3 phase, existing as a metastable state, is observable solely at elevated temperatures and is susceptible to degradation into the δ‐phase in ambient air. Therefore, the attainment of phase‐stable α‐FAPbI3 in ambient conditions has become a crucial objective in perovskite research. Here, we proposed an efficient conversion process of PbI2 into the α‐FAPbI3 perovskites in ambient air. This conversion was facilitated by the introduction of chelating molecules, which interacted with PbI2 to form an intermediate phase. Due to the reduced formation barrier resulting from the altered reaction pathway, this stable intermediate phase transitioned directly into α‐FAPbI3 upon the deposition of the organic cation solution, effectively bypassing the formation of δ‐FAPbI3. Consequently, the ambient‐fabricated FAPbI3 perovskite solar cells (PSCs) exhibited an outstanding power conversion efficiency of 25.08 %, along with a high open‐circuit voltage of 1.19 V. Furthermore, the unencapsulated devices demonstrated remarkable environmental stability. Notably, this innovative approach promises broad applicability across various chelating molecules, opening new avenues for further progress in the ambient air fabrication of FAPbI3 PSCs.

Reaction Mechanism and Structural Evolution of Tunnel‐Structured KCu7S4 Nanowires in Li+/Na+‐Ion Batteries

AbstractSelecting suitable electrode materials for sodium‐ion batteries (SIBs) often relies on the experience gained from lithium‐ion batteries (LIBs), particularly in terms of thermodynamics. However, this approach may fall into a stagnant situation where the development of SIBs consistently lags behind that of LIBs due to the larger ionic radius of Na+. Accordingly, it is crucial to establish a dedicated selection rule specifically tailored for SIB electrodes to overcome this challenge. Herein, a screening method is proposed for SIB materials, where an ideal candidate shall form a stable intermediate transition phase with Na+. This phase acts as an important bridge that can regulate the insertion/extraction of charge carriers. Atomically resolved transmission electron microscopy demonstrates that KCu7S4 can react with Na+ to form a stable intermediate phase (Na3Cu4S4). Na3Cu4S4 can undergo reversible conversion reactions, contribute capacity, stabilize the tunnel structure and enhance the migration/diffusion of Na+. In contrast, Li+ can't form a stable intermediate phase in KCu7S4 during lithiation/delithiation, thus losing the ability to effectively regulate Li+ insertion/extraction. These findings provide valuable insights for the development of suitable electrode materials for SIBs, emphasizing the importance of stable intermediate phases in regulating charge carrier insertion/extraction and improving overall battery performance.

Micromechanism for Copper-Deficiency Enhanced Stability: A Quasi In Situ TEM Study of Electric-Induced Structural Evolution in Cu2-x(S, Se) Liquid-Like Thermoelectric Materials.

Cu-based liquid-like thermoelectric materials have garnered tremendous attention due to their inherent ultralow lattice thermal conductivity. However, their practical application is hampered by stability issues under a large current or temperature gradient. It has been reported that introduction of copper vacancies can enhance the chemical stability, whereas the micromechanism behind this macroscopic improvement still remains unknown. Here, we have established a quasi in situ TEM method to examine and compare the structural evolution of Cu2-xS0.2Se0.8 (x = 0, 0.05) under external electric fields. It is then found that the preset Cu vacancies could favor the electric-induced formation of a more stable intermediate phase, i.e., the hexagonal CuSe-type structure in the form of either lamellar defects (majorly) or long-range order (minorly), in which ordering of S and Se also occurred. Thereby, copper and chalcogen atoms could largely be solidified into the matrix, and the elemental deposition and evaporation process is mitigated under an electric field.

Boosting CsSnI3‐based near‐infrared perovskite light‐emitting diodes performance via solvent coordination engineering

AbstractDue to their unique photoelectric properties, nontoxic tin‐based perovskites are emerging candidates for efficient near‐infrared LEDs. However, the facile oxidation of Sn2+ and the rapid crystallization rate of tin‐based perovskites result in suboptimal film quality, leading to inferior efficiencies of tin‐based perovskite light‐emitting diodes (Pero‐LEDs). In this study, we investigate the influence of commonly used solvents on the quality of the CsSnI3 films. Remarkably, DMSO exhibits a stronger interaction with SnI2, forming a stable intermediate phase of SnI2·3DMSO. This intermediate effectively inhibits the oxidation of Sn2+ and slows down the crystallization rate, bringing in lower defect state density and higher photoluminescence quantum yield of the prepared perovskite films. Consequently, the corresponding Pero‐LEDs achieve a maximum external quantum efficiency (EQE) of 5.6%, among the most efficient near‐infrared Pero‐LEDs. In addition, the device processes ultra‐low efficiency roll‐off and high reproducibility. Our research underscores the crucial role of solvent‐perovskite coordination in determining film quality. These findings offer valuable guidance for screening solvents to prepare highly efficient and stable tin‐based perovskites.

Ti4+ substitution suppressing P2-O2 phase transition to construct stable P2-Na0.67Ni0.33Mn0.67O2 cathode for long-term durable sodium-ion batteries

Due to high safety and cost-effective resources, sodium-ion batteries show great prospect in large-scale energy storage systems. Owing to wide structural framework and high theoretical capacity, Na-based layered oxide with prismatic P2-type structure is an ideal cathode candidate for sodium-ion batteries. However, Na-based layered compounds always suffer from detrimental multiple phase transitions during cycle period, resulting in structure deterioration and rapid capacity decay. Herein, stable P2-Na0.67Ni0.33Mn0.67-xTixO2 cathodes are constructed through substituting Mn with Ti. In-situ XRD demonstrates that Ti substitution effectively successfully suppresses the undesired phase transition of P2-O2, and in turn appears a stable Z-symbiotic intermediate phase with minimal volume change. Hence, designed P2-Na0.67Ni0.33Mn0.37Ti0.3O2 cathode shows better structural stability and long-term cycling reliability, yielding a high reversible capacity of 123 mAh g−1 and a high capacity retention of 89 % after 100 cycles at 0.2C. More importantly, a high working voltage of 3.5 V and a boosted energy density of 400 Wh kg−1 is achieved in the NNMTO-3 || HC full cell, which further strengthens the competence of Ti-substituted Na-based layered oxide cathodes. This work provides a feasible design insight for long-life, high-voltage sodium-ion batteries, which can be applied to construct more stable layered compounds and further improves their electrochemical properties.

Microstructural Transformations in Solid-State Annealed Al/Ag/Al Diffusion Couples Examined via High-Voltage Electron Microscopy (HVEM)

This study focuses on the practical relevance of the Al-Ag bonding interface in electronic device fabrication, particularly in wire bonding, which is crucial for enhancing component reliability and performance. Experiments involved Al/Ag/Al diffusion couples, annealed at 703 K, revealing two stable intermediate phases, μ and δ. Characterizing the intermediate phases’ compositions and concentration profiles exposed a vital transition at the δ-Al interface. We used high-voltage electron microscopy (HVEM) to examine crystal structure evolution, identifying a (hexagonal close-packed) hcp structure in the intermediate phase between δ and Al, matching the δ phase. Notably, a substantial microstructural transformation occurred within the Ag-Al diffusion couple, as nano-sized precipitates transitioned from spherical to plate-like, along specific {111} planes, reflecting the evolution from off-stoichiometric, disordered phases to ordered ones. Mapping the concentrations of intermediate phases on the Al-Ag phase diagram revealed shifted and narrower solubility ranges compared to the calculations. This study provides insight into the crystal structure and microstructure changes during diffusion in Al/Ag/Al diffusion couples, holding implications for electronic device fabrication. Understanding intermediate phase behavior and evolution is vital in this context, potentially influencing materials development and process optimization in the electronic components industry, and thus, enhancing device performance and reliability.

Volatile Dual‐Solvent Assisted Intermediate Phase Regulation for Anti‐Solvent‐Free Perovskite Photovoltaics

AbstractThe unprecedented development of perovskite solar cells (PSCs) makes them one of the most promising candidates for terawatt‐scale green energy production with low cost. However, the high boiling point solvents during the solution‐processed film deposition cause anisotropic crystal growth and toxic solvent vapor during high‐throughput manufacturing. Here, a dual‐component green solvent consisting of isopropyl acetate and acetonitrile is proposed to form a volatile perovskite precursor, which can realize the high‐quality perovskite thin film deposition by intermediate phase regulation. A room‐temperature stable perovskite intermediate phase is constructed with the engagement of isopropyl acetate as co‐solvent, which suppresses the exploding nucleation rate in volatile perovskite precursor, providing a fine grain growth rate and wide processing window in scalable film deposition. The corresponding PSCs fabricated by blade coating without anti‐solvents or gas quenching achieve power conversion efficiency (PCE) of 16.37 % and 15.29 % for the areas of 14.08 cm2 and 37.83 cm2, respectively.

Volatile Dual-Solvent Assisted Intermediate Phase Regulation for Anti-Solvent-Free Perovskite Photovoltaics.

The unprecedented development of perovskite solar cells (PSCs) makes them one of the most promising candidates for terawatt-scale green energy production with low cost. However, the high boiling point solvents during the solution-processed film deposition cause anisotropic crystal growth and toxic solvent vapor during high-throughput manufacturing. Here, a dual-component green solvent consisting of isopropyl acetate and acetonitrile is proposed to form a volatile perovskite precursor, which can realize the high-quality perovskite thin film deposition by intermediate phase regulation. A room-temperature stable perovskite intermediate phase is constructed with the engagement of isopropyl acetate as co-solvent, which suppresses the exploding nucleation rate in volatile perovskite precursor, providing a fine grain growth rate and wide processing window in scalable film deposition. The corresponding PSCs fabricated by blade coating without anti-solvents or gas quenching achieve power conversion efficiency (PCE) of 16.37% and 15.29% for the areas of 14.08 cm2 and 37.83 cm2, respectively.

Stable intermediate phase of secondary structures for semiflexible polymers.

Systematic microcanonical inflection-point analysis of precise numerical results obtained in extensive generalized-ensemble Monte Carlo simulations reveals a bifurcation of the coil-globule transition line for polymers with a bending stiffness exceeding a threshold value. The region, enclosed by the toroidal and random-coil phases, is dominated by structures crossing over from hairpins to loops upon lowering the energy. Conventional canonical statistical analysis is not sufficiently sensitive to allow for the identification of these separate phases.

Near room temperature stepwise spin state switching and photomagnetic effect in a mixed-valence molecular square.

A two-step thermo-induced spin-state switching was observed in a cyanide-bridged [Fe2Fe2] molecular square complex, {[Fe(pzTp)(CN)3]2[Fe(L)2]2}[Fe(pzTp)(CN)3]2·4CH3OH·2H2O [1·4MeOH·2H2O; pzTp = tetrakis(pyrazol-1-yl)borate and L = bis(1-ethylimidazol-2-yl)ketone (bik*)], which was characterized fully by single-crystal X-ray diffraction, (photo)magnetic measurements, and spectroscopic techniques. 1·4MeOH·2H2O exhibited a two-step thermo-induced spin transition with T1/2 (1) ↑ = 306 K and T1/2 (2) ↑ = 370 K converting the low-temperature ground state, {[(FeIIILS)2(FeIILS)2](FeIIILS)2} into the high-temperature state, {[(FeIIILS)2(FeIIHS)2](FeIIILS)2} via a stable intermediate phase. The desolvated phase, 1 also exhibited a gradual but reversible thermo-induced spin state change with a T1/2 value of 190 K, significantly shifted to a lower temperature. It also exhibited photo-induced spin-state switching at 20 K with the TLIESST value of 60 K.

Photo-catalytic transparent glass-ceramics containing Zn2TiO4 nanocrystals

Photo-catalytic active glass-ceramics have good application prospects in addressing environmental problems and offer advantages over traditional photo-catalyst. Photo-catalytic properties of glass-ceramics mainly depends on the presence of photo-catalytic active nanocrystals embedded inside. Zn2TiO4, as a stable intermediate phase of TiO2-ZnO system, has comparative photo-catalytic activities with traditional photo-catalyst TiO2 and ZnO. In this work, colorless and highly transparent glass-ceramics containing Zn2TiO4 nanocrystals are successfully prepared, and effects of crystallization on microstructure, mechanical, photo-catalytic and recyclable properties are investigated. These Zn2TiO4 nanocrystals embedded glass-ceramics are found to be photo-catalytically active and efficient in photo-degradation of organic dyes. These results show that glass-ceramics containing photo-catalytic nanocrystals are promising for degradation of organic pollutants.

Moisture-dependent room-temperature perovskite crystallization in vacuum flash-assisted solution processed intermediate phase films

We propose a straightforward intermediate-phase strategy to facilitate large-area crystallization of perovskite under room-temperature: preparing intermediate phase film with vacuum flash-assisted solution processing (VASP) method and performing controlled moisture-exposure subsequently. Moisture molecules penetrate into the whole intermediate film, remove residual solvent molecules, and trigger room-temperature crystallization of perovskite in a wide humidity range (25–80% RH), while negligible hydroxyl species are observed in the intermediate phase and resultant perovskite films. Without antisolvent, thermal-annealing and additive, high-humidity (80% RH) exposure of intermediate-phase film under room-temperature results in crystalline perovskite with a 8× increase in grain size and a 6× increase in photoluminescence lifetime, which is attributed to the homogenous and stable intermediate phase prepared by VASP and the synergistic effect of H 2 O and residual solvent molecules. Without antisolvent, thermal-annealing and additive, high-humidity (80% RH) exposure of intermediate-phase precursor film under room-temperature results in crystalline perovskite with a 8× increase in grain size and a 6× increase in photoluminescence lifetime. • The intermediate phase strategy applies in the wide range of 25–80% RH humidity. • Moisture exposure under room-temperature induces identical chemical transition. • Negligible hydroxyl species are observed in perovskite and its intermediate. • 80% RH exposure leads micron-size grains and microsecond fluorescence lifetime.

Efficient Ideal‐Bandgap Tin–Lead Alloyed Inorganic Perovskite Solar Cells Enabled by Structural Dimension Engineering

AbstractInorganic tin–lead alloyed perovskite solar cells with optimal bandgap have gained increasing attention because of their higher theoretical efficiency limit, inherently robust stability, and potentials in all‐inorganic perovskite tandems. However, their efficiency has far lagged from their Pb‐based counterparts owing to some intractable problems such as poor crystallization and facile Sn2+oxidation. Here, a small amount of 2D perovskite PEAPb0.7Sn0.3I4is utilized to regulate the crystallization process of 3D CsPb0.7Sn0.3I3based on the temperature‐gradient annealing method. The X‐ray diffraction results show that a stable intermediate phase composed of 3D perovskite seeds and 2D phases is formed under a lower annealing temperature of 50 °C, and the pre‐crystallized 3D perovskites can promote the subsequent crystallization upon 80 °C annealing to attain high quality film. It is interesting that the 2D perovskite phase is ultimately mainly located between the 3D perovskite phase and hole transport layer as revealed by the time of flight‐secondary ion mass spectrometry. The resulting perovskite exhibits a lower extent of non‐radiative recombination and better stability. Consequently, the device achieves a champion efficiency of 14.6% setting a new record for inorganic tin‐lead perovskite solar cells (PSCs). This work sheds more light on the future progress of inorganic tin‐lead PSC.

Interplay of magnetic field and trigonal distortion in the honeycomb Γ model: Occurrence of a spin-flop phase

In candidate Kitaev materials, the off-diagonal $\Gamma$ and $\Gamma'$ interactions are identified to come from the spin-orbit coupling and trigonal distortion, respectively. They have generated intense research efforts because of their intimate relation to the field-induced magnetically disordered state reported in $\alpha$-RuCl$_3$. Theoretically, while a plethora of field-induced phases has been proposed in the honeycomb lattice, a stable intermediate phase that can survive in a wide parameter region regardless of the underlying phases is still lacking. Here we focus on the interplay of an out-of-plane magnetic field and a symmetry-allowed $\Gamma'$ term due to trigonal distortion in the dominant antiferromagnetic $\Gamma$ region. By using multifaceted approaches ranging from classical Monte Carlo and semiclassical spin-wave theory to density-matrix renormalization group, we identify an intriguing spin-flop phase in the presence of magnetic field and antiferromagnetic $\Gamma'$ interaction, before it eventually enters into a fully polarized state. As the $\Gamma'$ interaction approaches the size of $\Gamma$ one, the $\Gamma$-$\Gamma'$ model maps to the easy-axis XXZ antiferromagnet, where the spin-flop phase can be understood as a superfluid phase in the extended Bose-Hubbard model. Our finding thus demonstrates an exciting path from the honeycomb $\Gamma$ model towards a $U(1)$-symmetric XXZ antiferromagnet in a magnetic field.

Supramolecular meso-Trick: Ambidextrous Mirror Symmetry Breaking in a Liquid Crystalline Network with Tetragonal Symmetry.

Bicontinuous and multicontinuous network phases are among nature's most complex structures in soft matter systems. Here, a chiral bicontinuous tetragonal phase is reported as a new stable liquid crystalline intermediate phase at the transition between two cubic phases, the achiral double gyroid and the chiral triple network cubic phase with an I23 space group, both formed by dynamic networks of helices. The mirror symmetry of the double gyroid, representing a meso-structure of two enantiomorphic networks, is broken at the transition to this tetragonal phase by retaining uniform helicity only along one network while losing it along the other one. This leads to a conglomerate of enantiomorphic tetragonal space groups, P41212 and P43212. Phase structures and chirality were analyzed by small-angle X-ray scattering (SAXS), grazing-incidence small-angle X-ray scattering (GISAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge, and model-dependent SAXS/RSoXS simulation. Our findings not only lead to a new bicontinuous network-type three-dimensional mesophase but also reveal a mechanism of mirror symmetry breaking in soft matter by partial meso-structure racemization at the transition from enantiophilic to enantiophobic interhelical self-assembly.

In-situ introduction of highly active TiO for enhancing hydrogen storage performance of LiBH4

• A valid strategy to in-situ introduce highly active additive to LiBH 4 is employed. • TiO is in-situ introduced into LiBH 4 and the LiBH 4 -0.06TiO system is obtained. • Enhanced kinetics and favorable cycling stability are achieved for the system. • Li 3 BO 3 and TiH 2 are generated and act as catalysts for LiBH 4 . • Dehydrogenation energy barrier is reduced and formation of Li 2 B 12 H 12 is inhibited. LiBH 4 is a promising candidate for solid state hydrogen storage, however, it still suffers from high hydrogen desorption temperature, harsh hydrogen absorption conditions, and poor reversibility, which hinder its practical development. In this paper, a novel synthetic strategy of heat treating a LiBH 4 and Ti(OEt) 4 mixture is employed to prepare LiBH 4 system with TiO in-situ introduced. With an optimized TiO content of 0.06 in molar fraction, the LiBH 4 -0.06TiO system shows onset and peak dehydrogenation temperatures of 240 °C and 340 °C, respectively, which are 140 °C and 90 °C lower than those of the pure LiBH 4 . The LiBH 4 -0.06TiO system can rapidly release 9 wt% H 2 after dwelling at 400 °C for 10 min. The hydrogenation of the dehydrogenation product initiates at 150 °C, and a capacity of 9 wt% is reached after isothermal dwelling at 500 °C under 50 bar of H 2 for 100 min. The capacity retention of the system can reach 74.4% after 10 cycles, indicating a favorable reversibility. With the introduction of TiO, the apparent dehydrogenation activation energy of the system is evidently reduced, and the formation of Li 2 B 12 H 12 , a highly thermal stable intermediate phase, is greatly suppressed. In addition, the aggregation is evidently alleviated. All of these contribute to the enhanced dehydrogenation kinetics and reversibility. TiO reacts with LiBH 4 , forming Li 3 BO 3 and TiH 2 after the initial dehydrogenation, which play significant catalytic effect to LiBH 4 .

A new thermodynamically stable Nb2Ni intermetallic compound phase revealed by peritectoid transition within binary Nb-Ni alloy system

A new intermetallic compound of thermodynamically stable Nb2Ni phase is discovered within Nb-Ni binary system, refreshing the current situation that there are only three stable intermediate phases of Nb7Ni6, NbNi3 and NbNi8. The new stable phase is generated from the peritectoid transition: (Nb) + Nb7Ni6 → Nb2Ni, and the transformation temperature is 1533 K. This refreshes the current equilibrium Nb-Ni binary phase diagram. It is confirmed by transmission electron microscopy and the annealing experiments, which is determined to be the FCC structure (Pearson: cF96, space grope: Fd-3m O2, a = 11.888 Å). Furthermore, the equilibrium properties of Nb2Ni phase are produced by density functional theory, including the formation energy, cohesive energy, bulk modulus and lattice constant.

Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters

Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.