Moderate Fields, Maximum Potential: Achieving High Records with Temperature-Stable Energy Storage in Lead-Free BNT-Based Ceramics

The increasing awareness of environmental concerns has prompted a surge in the exploration of lead-free, high-power ceramic capacitors. Ongoing efforts to develop lead-free dielectric ceramics with exceptional energy-storage performance (ESP) have predominantly relied on multi-component composite strategies, often accomplished under ultrahigh electric fields. However, this approach poses challenges in insulation and system downsizing due to the necessary working voltage under such conditions. Despite extensive study, bulk ceramics of (Bi0.5Na0.5)TiO3 (BNT), a prominent lead-free dielectric ceramic family, have seldom achieved a recoverable energy-storage (ES) density (Wrec) exceeding 7 J cm-3. This study introduces a novel approach to attain ceramic capacitors with high ESP under moderate electric fields by regulating permittivity based on a linear dielectric model, enhancing insulation quality, and engineering domain structures through chemical formula optimization. The incorporation of SrTiO3 (ST) into the BNT matrix is revealed to reduce the dielectric constant, while the addition of Bi(Mg2/3Nb1/3)O3 (BMN) aids in maintaining polarization. Additionally, the study elucidates the methodology to achieve high ESP at moderate electric fields ranging from 300 to 500 kV cm-1. In our optimized composition, 0.5(Bi0.5Na0.4K0.1)TiO3-0.5(2/3ST-1/3BMN) (B-0.5SB) ceramics, we achieved a Wrec of 7.19 J cm-3 with an efficiency of 93.8% at 460 kV cm-1. Impressively, the B-0.5SB ceramics exhibit remarkable thermal stability between 30 and 140 °C under 365 kV cm-1, maintaining a Wrec exceeding 5 J cm-3. This study not only establishes the B-0.5SB ceramics as promising candidates for ES materials but also demonstrates the feasibility of optimizing ESP by modifying the dielectric constant under specific electric field conditions. Simultaneously, it provides valuable insights for the future design of ceramic capacitors with high ESP under constraints of limited electric field.

A2LiGaI6 (A = Cs, Rb): New lead-free and direct bandgap halide double perovskites for IR application

Recently, all inorganic double perovskites have drawn a lot of interest as promising solar materials. The optical, structural, thermoelectric, electronic, and mechanical properties of double halide perovskites A2LiGaI6 (A = Cs, Rb) are explored via first-principles calculations with the WIEN2k code, using GGA PBEsol and TB-mBJ potentials. The majority of perovskite materials utilized in the highest-performing solar cells have bandgaps ranging between 1.48 and 1.62 eV. The compounds A2LiGaI6 (A = Cs, Rb) have a direct bandgap of 1.51 eV and 1.55 eV, respectively, and are expected to be useful in solar cells. The optical study shows that there are large absorption bands in the visible region, as determined by the dielectric constant, absorption, and other dependent factors. Their potential for use in solar cells is increased by their absorption in the visible part. The BoltzTraP code has been used to perform thermoelectric studies to assess the electrical, thermal conductivities, and Seebeck coefficient. They are important for construction of thermoelectric generators that harvest heat energy because of their high figure of merit and incredibly low thermal conductivity of lattice at ambient temperature. Furthermore, by examining the spectroscopic limit maximum efficiency, up to 30 % efficiency is predicted for both compositions, which paves the way for the applicability of them in solar energy conversion.

Bluish-white Light-emitting 2D Sheets of Lead-free Perovskite Cesium Titanium Bromide (CsTiBr3) by a Two-stage Deposition Technique

Bluish-white light-emitting materials are commonly used in LED lighting because they produce natural-looking light. Here we report the photoluminescent emission (PL) of novel, two-dimensional lead-free CsTiBr3 perovskite prepared via a two-stage deposition process. The formation of two-dimensional nanosheets of CsTiBr3 perovskite is confirmed by XRD, EDAX, and FESEM analysis. The height of the cesium bromide thin film substrate from the titanium bromide vapor source plays an important role in the formation of two-dimensional CsTiBr3. The CsTiBr3 perovskite nanosheets exhibit unique exciton- luminescence at 440 nm and self-trapped exciton emission at 595 nm which are the characteristics of two-dimensional halide structure, along with the band-to-band emission at 400 nm at an excitation wavelength of 340 nm. The resulting bluish-white light PL emission makes two-dimensional CsTiBr3 perovskite an alternative material to the traditional lead-based perovskite in LEDs, display technology, solid-state lighting, and various optoelectronic devices, addressing environmental concerns.

Paper-based sensor based on lead-free manganese halide for the determination of water content in organic solvents

A highly stable and luminescent lead-free manganese(II) halide hybrid MnBr₄(TMN)₂ (C₃₄H₄₂Br₄MnN₄) was designed and synthesized by introducing a large cationic organic spacer. The MnBr₄(TMN)₂ displays high luminescence with quantum yields up to 77% and possesses turn-off fluorescence behavior (E_x/E_m=365/546 nm) for water. These properties make the MnBr₄(TMN)₂ a promising candidate as an alternative indicator for the detection of water with potential applications for the fabrication of LEDs. Herein, a paper-based sensor based on MnBr₄(TMN)₂ is described for the determination of water content in organic solvents. The mechanism of water sensing can be tentatively explained by fluorescence quenching originating from the destruction of water due to the Mn-Br bonds of MnBr₄(TMN)₂. The MnBr₄(TMN)₂-based paper sensor exhibits an excellent discrimination ability of water content in the range 0-25.0% with a detection limit of 0.27%. Satisfactory recoveries (94.91±4.09% to 103.23±2.38%) are obtained in spiked ethanol solvent samples, which demonstrate that the MnBr₄(TMN)₂-based paper sensor is capable of detecting water content in real ethanol solvent samples.

Ligand Engineering in Tin-Based Perovskite Solar Cells

Perovskite solar cells (PSCs) have attracted aggressive attention in the photovoltaic field in light of the rapid increasing power conversion efficiency. However, their large-scale application and commercialization are limited by the toxicity issue of lead (Pb). Among all the lead-free perovskites, tin (Sn)-based perovskites have shown potential due to their low toxicity, ideal bandgap structure, high carrier mobility, and long hot carrier lifetime. Great progress of Sn-based PSCs has been realized in recent years, and the certified efficiency has now reached over 14%. Nevertheless, this record still falls far behind the theoretical calculations. This is likely due to the uncontrolled nucleation states and pronounced Sn (IV) vacancies. With insights into the methodologies resolving both issues, ligand engineering-assisted perovskite film fabrication dictates the state-of-the-art Sn-based PSCs. Herein, we summarize the role of ligand engineering during each state of film fabrication, ranging from the starting precursors to the ending fabricated bulks. The incorporation of ligands to suppress Sn2+ oxidation, passivate bulk defects, optimize crystal orientation, and improve stability is discussed, respectively. Finally, the remained challenges and perspectives toward advancing the performance of Sn-based PSCs are presented. We expect this review can draw a clear roadmap to facilitate Sn-based PSCs via ligand engineering.

Large Energy Capacitive High-Entropy Lead-Free Ferroelectrics

Advanced lead-free energy storage ceramics play an indispensable role in next-generation pulse power capacitors market. Here, an ultrahigh energy storage density of ~ 13.8 J cm-3 and a large efficiency of ~ 82.4% are achieved in high-entropy lead-free relaxor ferroelectrics by increasing configuration entropy, named high-entropy strategy, realizing nearly ten times growth of energy storage density compared with low-entropy material. Evolution of energy storage performance and domain structure with increasing configuration entropy is systematically revealed for the first time. The achievement of excellent energy storage properties should be attributed to the enhanced random field, decreased nanodomain size, strong multiple local distortions, and improved breakdown field. Furthermore, the excellent frequency and fatigue stability as well as charge/discharge properties with superior thermal stability are also realized. The significantly enhanced comprehensive energy storage performance by increasing configuration entropy demonstrates that high entropy is an effective but convenient strategy to design new high-performance dielectrics, promoting the development of advanced capacitors .

Lead-Free Perovskite Materials for Solar Cells

The toxicity issue of lead hinders large-scale commercial production and photovoltaic field application of lead halide perovskites. Some novel non- or low-toxic perovskite materials have been explored for development of environmentally friendly lead-free perovskite solar cells (PSCs). This review studies the substitution of equivalent/heterovalent metals for Pb based on first-principles calculation, summarizes the theoretical basis of lead-free perovskites, and screens out some promising lead-free candidates with suitable bandgap, optical, and electrical properties. Then, it reports notable achievements for the experimental studies of lead-free perovskites to date, including the crystal structure and material bandgap for all of lead-free materials and photovoltaic performance and stability for corresponding devices. The review finally discusses challenges facing the successful development and commercialization of lead-free PSCs and predicts the prospect of lead-free PSCs in the future.

Investigating the property of water driven lead-free stable inorganic halide double perovskites

Lead free halide double perovskite materials, A₂BB́X₆ (where A, B and B́ are cations and X is a halide anion) have achieved considerable attention in the field of optoelectronic devices due to their high thermal along with the moisture stability and less toxicity as lead halide perovskites suffer from the stability and toxicity issues which inhibit them to be commercialized. Therefore, synthesis of low cost and stable perovskite materials are the main focus of perovskite family nowadays. Herein, we have reported lead free Cs₂AgBiCl₆ and Cs₂AgBiBr₆ double perovskite microcrystals in both organic and a mixture of the aqueous-organic medium. Our studies are not only eradicating the toxicity of lead but also explored towards the stability of perovskite materials in the aqueous medium. Morphology is investigated using SEM and TEM imaging along with the enhancement in emission peak by increasing the content of water.

China's progress of perovskite solar cells in 2019

Perovskite solar cells (PSCs) have attracted worldwide attention due to their high efficiency and low manufacturing cost. As the largest supplier of photovoltaic modules, China has made huge endeavors in the research on PSCs. In 2019, Chinese research groups were still holding the top position for paper publications in the world. Both the efficiency and the stability of the device have been steadily increasing, pushing forward the commercialization of PSCs step by step. This review summarizes the highlights of China's PSC research progress in 2019 and briefly introduces the development of PSC modules in industry.

Inorganic antimony halide hybrids with broad yellow emissions

Lead halide perovskites exhibit unexceptionable photoelectric properties. However, these materials are unsatisfactory in terms of stability and toxicity. Herein, we report Rb₇Sb₃Cl₁₆ as a new kind of lead free perovskite variants. This material can be easily obtained through hydrothermal reactions. The composition is determined through structure refinement, elemental analysis and X-ray photoelectron spectra. Rb₇Sb₃Cl₁₆ exhibits a broad yellow emission at 560 nm, with a Stokes shift of 175 nm and a photoluminescence quantum yield (PLQY) around 26%. Rb₇Sb₃Cl₁₆ also shows good thermal and water stability due to its inorganic composition. White light-emitting diodes (LEDs) are constructed by combining Rb₇Sb₃Cl₁₆ as yellow phosphors, our previously reported Cs₂SnCl₆:2.75%Bi as blue phosphors, and commercial UV LED chips as the excitation source, producing a white light with the Commission Internationale de'Eclairage (CIE) color coordinates at (0.39, 0.38).

Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 lead-free piezoceramic system

This paper is concerned with the development of a piezoelectric d₁₅ shear-induced torsion actuator made of a lead-free piezoceramic material exhibiting giant piezoelectric shear stress coefficient (e₁₅) and piezoelectric transverse shear actuation force comparable to that of lead-based shear-mode piezoceramics. The Mn-modified 0.93(Na_0.5Bi_0.5TiO₃)-0.07BaTiO₃ (NBT-BT-Mn) composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C m^-2. The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d₁₅ mode piezoceramic shear patches, provided a rate of twist of 0.08 mm m^-1 V^-1 under quasi-static 150 V drive. The high value of piezoelectric shear d₁₅ coefficient in NBT-BT-Mn sample further demonstrated its potential in practical applications. These results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts.

Effect of ultrasonic vibration time on the Cu/Sn-Ag-Cu/Cu joint soldered by low-power-high-frequency ultrasonic-assisted reflow soldering

Techniques to improve solder joint reliability have been the recent research focus in the electronic packaging industry. In this study, Cu/SAC305/Cu solder joints were fabricated using a low-power high-frequency ultrasonic-assisted reflow soldering approach where non-ultrasonic-treated samples were served as control sample. The effect of ultrasonic vibration (USV) time (within 6s) on the solder joint properties was characterized systematically. Results showed that the solder matrix microstructure was refined at 1.5s of USV, but coarsen when the USV time reached 3s and above. The solder matrix hardness increased when the solder matrix was refined, but decreased when the solder matrix coarsened. The interfacial intermetallic compound (IMC) layer thickness was found to decrease with increasing USV time, except for the USV-treated sample with 1.5s. This is attributed to the insufficient USV time during the reflow stage and consequently accelerated the Cu dissolution at the joint interface during the post-ultrasonic reflow stage. All the USV-treated samples possessed higher shear strength than the control sample due to the USV-induced-degassing effect. The shear strength of the USV-treated sample with 6s was the lowest among the USV-treated samples due to the formation of plate-like Ag₃Sn that may act as the crack initiation site.

Core-shell grain structures and ferroelectric properties of Na0.5K0.5NbO3-LiTaO3-BiScO3 piezoelectric ceramics

Legislation arising from health and environmental concerns has intensified research into finding suitable alternatives to lead-based piezoceramics. Recently, solid solutions based on sodium potassium niobate (K,Na)NbO3 (KNN) have become one of the globally-important lead-free counterparts, due to their favourable dielectric and piezoelectric properties. This data article provides information on the ferroelectric properties and core-shell grain structures for the system, (1-y)[(1-x)Na0.5K0.5NbO3 - xLiTaO3] - yBiScO3 (x=0-0.1, y=0.02, abbreviated as KNN-xLT-2BS). We show elemental analysis with aid of TEM spot-EDX to identify three-type grain-types in the KNN-LT-BS ternary system. Melting behaviour has been assessed using a tube furnace with build-in camera. Details for the ferroelectric properties and core-shell chemical segregation are illustrated.