In-Situ Construction of Electronically Insulating and Air-Stable Ionic Conductor Layer on Electrolyte Surface and Grain Boundary to Enable High-Performance Garnet-Type Solid-State Batteries.

Lithophobic Li2CO3/LiOH contaminants and high-resistance lithium-deficient phases produced from the exposure of garnet electrolyte to air leads to a decrease in electrolyte ion transfer ability. Additionally, garnet electrolyte grain boundaries (GBs) with narrow bandgap and high electron conductivity are potential channels for current leakage, which accelerate Li dendrites generation, ultimately leading to short-circuiting of all-solid-state batteries (ASSBs). Herein, a stably lithiophilic Li2ZO3 is in situ constructed at garnet electrolyte surface and GBs by interfacial modification with ZrO2 and Li2CO3 (Z+C) co-sintering to eliminate the detrimental contaminants and lithium-deficient phases. The Li2ZO3 formed on the modified electrolyte (LLZTO-(Z+C)) surface effectively improves the interfacial compatibility and air stability of the electrolyte. Li2ZO3 formed at GBs broadens the energy bandgaps of LLZTO-(Z+C) and significantly inhibits lithium dendrite generation. More Li+ transport paths found in LLZTO-Z+C by first-principles calculations increase Li+ conductivity from 1.04×10-4 to 7.45×10-4 S cm-1. Eventually, the Li|LLZTO-(Z+C)|Li symmetric cell maintains stable cycling for over 2000 h at 0.8 mA cm-2. The capacity retention of LiFePO4|LLZTO-(Z+C)|Li battery retains 70.5% after 5800 ultralong cycles at 4 C. This work provides a potential solution to simultaneously enhance the air stability and modulate chemical characteristics of the garnet electrolyte surface and GBs for ASSBs.

An ITO-Free Kesterite Solar Cell.

Photovoltaic thin film solar cells based on kesterite Cu2 ZnSn(S, Se)4 (CZTSSe) have reached 13.8% sunlight-to-electricity conversion efficiency. However, this efficiency is still far from the Shockley-Queisser radiative limit and is hindered by the significant deficit in open circuit voltage (VOC ). The presence of high-density interface states between the absorber layer and buffer or window layer leads to the recombination of photogenerated carriers, thereby reducing effective carrier collection. To tackle this issue, a new window structure ZnO/AgNW/ZnO/AgNW (ZAZA) comprising layers of ZnO and silver nanowires (AgNWs) is proposed. This structure offers a simple and low-damage processing method, resulting in improved optoelectronic properties and junction quality. The ZAZA-based devices exhibit enhanced VOC due to the higher built-in voltage (Vbi ) and reduced interface recombination compared to the usual indium tin oxide (ITO) based structures. Additionally, improved carrier collection is demonstrated as a result of the shortened collection paths and the more uniform carrier lifetime distribution. These advances enable the fabrication of the first ITO-free CZTSSe solar cells with over 10% efficiency without an anti-reflective coating.

The Multiple Roles of Na Ions in Highly Efficient CZTSSe Solar Cells.

Sodium (Na) doping is a well-established technique employed in chalcopyrite and kesterite solar cells. While various improvements can be achieved in crystalline quality, electrical properties, or defect passivation of the absorber materials by incorporating Na, a comprehensive demonstration of the desired Na distribution in CZTSSe is still lacking. Herein, a straightforward Na doping approach by dissolving NaCl into the CZTS precursor solution is proposed. It is demonstrated that a favorable Na ion distribution should comprise a precisely controlled Na+ concentration at the front surface and an enhanced distribution within the bottom region of the absorber layer. These findings demonstrated that Na ions play several positive roles within the device, leading to an overall power conversion efficiency of 12.51%.

A photodetector fabricated from 2H-PbI2 micro-crystals recycled from waste lead acid batteries.

Recycling Pb from lead acid batteries is rather important in environmental protection, but current strategies need a high temperature or produce secondary pollution. Herein, we present a green reactant recycling method to synthesize PbI2 micro-crystals by extracting the Pb from waste lead acid batteries. Systematical characterizations indicate that the as-prepared PbI2 micro-crystals show high purity, high crystal quality with a 2H-hexagonal crystal structure, and excellent optical properties with a bandgap of 2.3 eV. Based on the recycled 2H-PbI2 micro-crystals, a symmetrically structured ITO/PbI2/ITO photodetector is fabricated. Under 10 V bias voltage, the device reveals a distinct photo-response to UV-visible light and superior performance, with a dark current of 1.06 nA, an on-off ratio of 103, a responsivity of 15.5 mA/W, and a detectivity of 4.7 × 1010 Hz1/2 W-1. In addition, the photodetector also exhibits relatively rapid response speeds of 69 ms (rise time) and 64 ms (decay time). Our study provides an innovative and green strategy for producing a UV-visible photodetector based on recycled lead acid batteries, which is significant in environmental protection and the recycling economy.

Sulfur-graded kesterite structured film drives improvement of VOC.

Realizing the graded bandgap in absorber layer is very essential for high efficient thin film solar cells. However, such bandgap modification in kesterite-structured Cu2ZnSnSe4 is normally realized via high temperature sulfurization process (above 500°C), which is not only difficult to control the sulfurization depth, but also introduces additional deep defects because of the decomposition of absorber layer at such high temperature. In this study, a low-temperature sulfurization process (150°C) is developed. Such process not only inhibits the decomposition of Cu2ZnSnSe4 films and controls the elemental distribution very well, but also increase the surface bandgap of the absorber layer and form a gradient energy bandgap. Also, the density of deep-level defects in the Cu2ZnSnSe4 layer is reduced. As a consequence, the open circuit voltage of the solar cell is improved by 60 mV. This study paves the way towards the high efficient kesterite solar cell and other solar cells.

Subsurface Engineering Induced Fermi Level De-pinning in Metal Oxide Semiconductors for Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-Ov ) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-Ov were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated Ov located at sub ∼2-5 nm region. Mott-Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm-2 at 1.23 V vs. RHE were achieved on BiVO4 , Bi2 O3 , TiO2 with outstanding stability for 72 h, outperforming most reported works under the identical conditions.

Study on the Adhesion Force Between Ga-Doped ZnO Thin Films and Polymer Substrates.

Flexible Ga doped ZnO (GZO) transparent conductive thin films were prepared on polycarbonate (PC) substrates at room temperature by magnetron sputtering. The adhesive property between the GZO film and the PC substrate was investigated quantitatively by the scratch test, which is designed for the quantitative assessment of the mechanical integrity of coated surfaces. The effect of the sputtering pressures on the adhesion forces for the GZO films was investigated. When the sputtering pressure varied from 0.2 to 0.5 Pa, no obvious adhesion force alteration was observed. However, when the sputtering pressure was increased to 0.7 Pa, the adhesion force was decreased. The lowest square resistance of the GZO film was 18.6 Ω/sq. Regardless of the sputtering pressure, the transmittance in the visible light was about 90%. When the sputtering pressure was 0.4 Pa, the optimal figure of merit (ΦTC) was 2.5×10-2 Ω-1, indicating that the optimal pressure was 0.4 Pa.

Transmission electron microscopy analysis for the process of crystallization of Cu2ZnSnS4 film from sputtered Zn/CuSn precursor.

The mechanism of crystallization of Cu2ZnSnS4 (CZTS) made by the sulfurization of a sputtered Zn/CuSn stack was studied by transmission electron microscopy. At 250 °C, the Zn buried at the bottom of the metallic stack was found to be driven to the upper layer by alloying with Cu and reacting with S to form ZnS. At 500 °C, CZTS was found to be formed and elemental Sn was observed in the vicinity of the back contact region, while large quantities of Cu2S and ZnS were segregated at the film surface. At 575 °C, Cu2SnS3 was found, while all the elemental Sn had vanished. Upon extending the duration of the annealing to 10 min, at 575 °C, all the secondary phases except ZnS were consumed and the CZTS formation was completed, while around 200 nm of MoS2 was formed between the CZTS layer and Mo back contact. The finished solar cell exhibits an efficiency of 2.66%, an open-circuit voltage of 666.9 mV and a short-circuit current density of 9.14 mA cm⁻². The solar cell performance is possibly limited by the thick MoS2 layer and the large density of voids in the back contact region due to the Sn loss at high sulfurization temperatures.

Self-assembling behavior of cellulose nanoparticles during freeze-drying: effect of suspension concentration, particle size, crystal structure, and surface charge.

Cellulose nanocrystals and cellulose nanofibers with I and II crystalline allomorphs (designated as CNC I, CNC II, CNF I, and CNF II) were isolated from bleached wood fibers by alkaline pretreatment and acid hydrolysis. The effects of concentration, particle size, surface charge, and crystal structure on the lyophilization-induced self-assembly of cellulose particles in aqueous suspensions were studied. Within the concentration range of 0.5 to 1.0 wt %, cellulose particles self-organized into lamellar structured foam composed of aligned membrane layers with widths between 0.5 and 3 µm. At 0.05 wt %, CNC I, CNF I, CNC II, and CNF II self-assembled into oriented ultrafine fibers with mean diameters of 0.57, 1.02, 1.50, and 1.00 µm, respectively. The size of self-assembled fibers became larger when more hydroxyl groups and fewer sulfates (weaker electrostatic repulsion) were on cellulose surfaces. Possible formation mechanism was inferred from ice growth and interaction between cellulose nanoparticles in liquid-crystalline suspensions.

Tailoring particle size of PbI2 towards efficient perovskite solar cells under ambient air conditions.

PbI2 films as templates are essential to the quality of perovskite (PVK) film in a two-step sequential deposition process. Herein, we demonstrate that PbI2 microcrystal powder (P-PbI2) of micrometer size is beneficial for preparing higher-quality PbI2 films in contrast to millimeter-sized PbI2 crystals (C-PbI2) under low relative humidity (RH) conditions. Surprisingly, C-PbI2 allowed the growth of denser films than P-PbI2 under heavy RH conditions. Ultimately, P-PbI2 gave PVK solar cells (PSCs) a best power conversion efficiency (PCE) of 23.30% under a low RH of 30 ± 5%, and C-PbI2 derived an impressive PCE of 21.09% when fabricated under conditions with RH = 50 ± 5%. This work provides ideas for the selection of lead iodide for the fabrication of PSCs under air conditions.

Nanoscale interface engineering of inorganic Solid-State electrolytes for High-Performance alkali metal batteries.

All-solid-state metal batteries (ASSMBs) have been regarded as the ideal candidate for the next-generation high-energy storage system due to their ultrahigh specific capacity and the lowest redox potential. However, the uncontrollable chemical reactivity during cycling which directly determines the growth behaviour of metal dendrites, the low coulombic efficiency and the safety concerns severely limit their real-world applications.. Crystallographic optimization based on solid-state electrolytes (SSEs) provides an atomic-scale and fundamental solution for the inhibition of dendrite growth in metal anodes, which has attracted widespread attentions. From this perspective, we summarize the recent advance of the crystallographic optimization for various classes of solid-state electrolytes. We highlight the recent experimental findings of crystallographic optimization for a new generation of all-solid-state batteries, including lithium-ion batteries, sodium-ion batteries, magnesium-ion batteries, with the aim of providing a deeper understanding of the crystallographic reactions in ASSMBs. The challenges and prospects for the future design and engineering of crystallographic optimization of SSEs are discussed, providing ideas for further research into crystallographic optimization to improve the performance of rechargeable batteries.

Highly Efficient Electrocatalytic N2 Reduction to Ammonia over Metallic 1T Phase of MoS2 Enabled by Active Sites Separation Mechanism.

The 1T phase of MoS2 has been widely reported to be highly active toward the hydrogen evolution reaction (HER), which is expected to restrict the competitive nitrogen reduction reaction (NRR). However, in this work, a prototype of active sites separation over 1T-MoS2 is proposed by DFT calculations that the Mo-edge and S atoms on the basal plane exhibit different catalytic NRR and HER selectivity, and a new role-playing synergistic mechanism is also well enabled for the multistep NRR, which is further experimentally confirmed. More importantly, a self-sacrificial strategy using g-C3 N4 as templates is proposed to synthesize 1T-MoS2 with an ultrahigh 1T content (75.44%, named as CNMS, representing the composition elements of C, N, Mo, and S), which yields excellent NRR performances with an ammonia formation rate of 71.07 µg h-1 mg-1 cat. at -0.5 V versus RHE and a Faradic efficiency of 21.01%. This work provides a promising new orientation of synchronizing the selectivity and activity for the multistep catalytic reactions.

Dual Protection of a Li-Ag Alloy Anode for All-Solid-State Lithium Metal Batteries with the Argyrodite Li6PS5Cl Solid Electrolyte.

All-solid-state lithium metal batteries (ASSLMBs) are considered promising candidates for next-generation energy storage systems. However, the growth of Li dendrites and interface side reactions hinder the practical application of ASSLMBs. To address these issues, a preformed Li-Ag alloy anode for an ASSLMB with the Li6PS5Cl electrolyte was constructed. The preformed Li-Ag alloy anode contains two distinct alloy layers, i.e., Li3Ag and Li0.98Ag0.02, with the former as a protection layer and the latter as a Li deposition site. Besides, a beneficial stable interlayer (Ag-P-S-Cl compound) produced by the reaction between Ag and Li6PS5Cl could work as a secondary protection layer between the anode and electrolyte. The dual protection (Li3Ag and Ag-P-S-Cl compound) suppresses dendritic growth and other interfacial issues effectively and simultaneously. Consequently, a LiCoO2/Li6PS5Cl/Li-Ag all-solid-state battery exhibits a remarkable specific capacity and excellent cycle stability. The dual-protection effect from the preformed Li-Ag alloy anode and the investigation of its working mechanism may enlighten a simple strategy for promoting the development of ASSLMBs.

4-Terminal Inorganic Perovskite/Organic Tandem Solar Cells Offer 22% Efficiency.

After fast developing of single-junction perovskite solar cells and organic solar cells in the past 10 years, it is becoming harder and harder to improve their power conversion efficiencies. Tandem solar cells are receiving more and more attention because they have much higher theoretical efficiency than single-junction solar cells. Good device performance has been achieved for perovskite/silicon and perovskite/perovskite tandem solar cells, including 2-terminal and 4-terminal structures. However, very few studies have been done about 4-terminal inorganic perovskite/organic tandem solar cells. In this work, semi-transparent inorganic perovskite solar cells and organic solar cells are used to fabricate 4-terminal inorganic perovskite/organic tandem solar cells, achieving a power conversion efficiency of 21.25% for the tandem cells with spin-coated perovskite layer. By using drop-coating instead of spin-coating to make the inorganic perovskite films, 4-terminal tandem cells with an efficiency of 22.34% are made. The efficiency is higher than the reported 2-terminal and 4-terminal inorganic perovskite/organic tandem solar cells. In addition, equivalent 2-terminal tandem solar cells were fabricated by connecting the sub-cells in series. The stability of organic solar cells under continuous illumination is improved by using semi-transparent perovskite solar cells as filter.

Insights on the Properties of the O-Doped Argyrodite Sulfide Solid Electrolytes (Li6PS5-xClOx, x=0-1).

Argyrodite sulfide solid electrolytes, such as Li6PS5Cl (LPSC), have received much attention due to their high ionic conductivity (>1 mS cm-1) and success in all-solid-state batteries (long cycle performance, high energy density, etc.). Numerous efforts are spent on modifying the properties of the electrolyte itself. Here, we combine first-principles calculations with experiments to investigate O-doped argyrodite sulfide solid electrolytes (Li6PS5-xClOx, x = 0-1). It is found that Li6PS4.75ClO0.25 (LPSCO0.25) with x = 0.25 and cubic phase (F4̅3 m) shows the highest ion conductivity of 4.7 mS cm-1 (cold-pressed), higher than that of undoped Li6PS5Cl (4.2 mS cm-1). The bare LiCoO2/LPSCO0.25/Li-In all-solid-state battery exhibits an initial capacity of 131 mA h g-1 at 0.1 C and satisfactory cycling stability with 86% capacity retention after 250 cycles to the 4th cycle at 0.3 C under 25 °C. In addition, the NCM811/LPSCO0.25/Li-In cell is assembled using bare LiNi0.83Co0.06Mn0.11O2 cathode and shows an initial discharge capacity of 181 mA h g-1 at 0.1 C and 160 mA h g-1 at 0.3 C. The doping of oxygen-forming Li6PS5-xClOx also improves the stability to Li metal, proven by cyclic voltammetry and powder X-ray diffraction tests. The calculation results for the band structure reveals that LPSC has the lowest unoccupied molecular orbital than LPSCO0.25, further confirming the above conclusion.

Porous Heteroatom-Doped Ti3C2Tx MXene Microspheres Enable Strong Adsorption of Sodium Polysulfides for Long-Life Room-Temperature Sodium-Sulfur Batteries.

The practical application of Na-S batteries is largely hindered by their low mass loading, inferior rate capability, and poor cycling performance. Herein, we report a design strategy for encapsulation of sodium polysulfides using Ti3C2Tx MXene. Porous nitrogen-doped Ti3C2Tx MXene microspheres have been synthesized by a facile synthesis method. Porous nitrogen-doped Ti3C2Tx MXene microspheres contain abundant pore structures and heteroatom functional groups for structural and chemical synergistic encapsulation of sodium polysulfides. Sodium-sulfur batteries, based on the as-proposed cathode, demonstrated outstanding electrochemical performances, including a high reversible capacity (980 mAh g-1 at 0.5 C rate) and extended cycling stability (450.1 mAh g-1 at 2 C after 1000 cycles at a high areal sulfur loading of 5.5 mg cm-2). This MXene-based hybrid material is a promising cathode host material for polysulfide-retention, enabling high-performance Na-S batteries.

A Green Lead Recycling Strategy from Used Lead Acid Batteries for Efficient Inverted Perovskite Solar Cells.

Lead is widely used as a crucial elemental for lead acid batteries (LABs) and emerging halide perovskite solar cells (PSCs). However, the use of soluble lead will raise environmental concerns. For the purpose of Pb recycling, herein, we report a reactant-recycling strategy to extract Pb from used LABs and synthesize high-purity PbI2. The recycled PbI2 shows smaller grain size, higher crystallinity, and higher thermal stability compared to the commercial sources. Perovskite films deposited with the high-quality PbI2 show larger grain size and fewer defects than the commercial ones. Consequently, the synthesized PbI2 enables a power conversation efficiency of 20.45% for the inverted MAPbI3 (MA= methylammonium) PSCs with excellent air stability. This work offers a novel strategy for lead recovery from LABs and a green path for the realization of high-performance PSCs with high defect tolerance.

Perovskite-based tandem solar cells.

The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit. An effective approach to realize high efficiency is to develop multi-junction cells. These years have witnessed the rapid development of organic-inorganic perovskite solar cells. The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells, by combining with silicon, Cu(In,Ga)Se2 and organic solar cells. In this review, we present the recent progress of perovskite-based tandem solar cells, including perovskite/silicon, perovskite/perovskite, perovskite/Cu(In,Ga)Se2, and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed.

Device Postannealing Enabling over 12% Efficient Solution-Processed Cu2 ZnSnS4 Solar Cells with Cd2+ Substitution.

Kesterite Cu2 ZnSnS4 is a promising photovoltaic material containing low-cost, earth-abundant, and stable semiconductor elements. However, the highest power conversion efficiency of thin-film solar cells based on Cu2 ZnSnS4 is only about 11% due to low open-circuit voltage and fill factor mainly caused by antisite defects and unfavorable heterojunction interface. In this work, a postannealing procedure is proposed to complete a Cd-alloyed Cu2 ZnSnS4 device. The postannealing to complete the device significantly enhances the performance of the indium tin oxide and promotes the moderate interdiffusion of elements between the layers in the device. As a result of the diffusion of Cu, Zn, In, and Sn, the interfacial electron and hole densities are improved, leading to the achievement of a suitable band alignment for carrier transport. The postannealing also reduces the interface traps and deep-level defects, contributing to decreased nonradiative recombination. Therefore, the open-circuit voltage and fill factor are both improved, and an efficiency over 12% for pure sulfide-based kesterite thin-film solar cells is obtained.

Defect Control for 12.5% Efficiency Cu2 ZnSnSe4 Kesterite Thin-Film Solar Cells by Engineering of Local Chemical Environment.

Kesterite-based Cu2 ZnSn(S,Se)4 semiconductors are emerging as promising materials for low-cost, environment-benign, and high-efficiency thin-film photovoltaics. However, the current state-of-the-art Cu2 ZnSn(S,Se)4 devices suffer from cation-disordering defects and defect clusters, which generally result in severe potential fluctuation, low minority carrier lifetime, and ultimately unsatisfactory performance. Herein, critical growth conditions are reported for obtaining high-quality Cu2 ZnSnSe4 absorber layers with the formation of detrimental intrinsic defects largely suppressed. By controlling the oxidation states of cations and modifying the local chemical composition, the local chemical environment is essentially modified during the synthesis of kesterite phase, thereby effectively suppressing detrimental intrinsic defects and activating desirable shallow acceptor Cu vacancies. Consequently, a confirmed 12.5% efficiency is demonstrated with a high VOC of 491 mV, which is the new record efficiency of pure-selenide Cu2 ZnSnSe4 cells with lowest VOC deficit in the kesterite family by Eg /q-Voc. These encouraging results demonstrate an essential route to overcome the long-standing challenge of defect control in kesterite semiconductors, which may also be generally applicable to other multinary compound semiconductors.