Ionic Bonding Without Directionality Facilitates Efficient Interfacial Bridging for Perovskite Solar Cells.

Interface passivation through Lewis acid-base coordinate chemistry in perovskite solar cells (PSCs) is a universal strategy to reduce interface defects and hinder ion migration. However, the formation of coordinate covalent bonding demands strict directional alignment of coordinating atoms. Undoubtedly, this limits the selected range of the interface passivation molecules, because a successful molecular bridge between charge transport layer and perovskite bottom interface needs a well-placed molecular orientation. In this study, it is discovered that potassium ions can migrate to the hollow sites of multiple iodine ions from perovskite to form K-Ix ionic bonding, and the ionic bonds without directionality can support molecular backbone rotation to facilitate polar sites (carboxyl groups) chelating Pb at the bottom perovskite interface, finally forming a closed-loop bonding structure. The synergy of coordinate and ionic bonding significantly reduces interface defects, changes electric field distribution, and immobilizes iodine at the perovskite bottom interface, resulting in eliminating the hysteresis effect and enhancing the performance of PSCs. As a result, the corresponding devices achieve a high efficiency exceeding 24.5% (0.09 cm2 ), and a mini-module with 21% efficiency (12.4 cm2 ). These findings provide guidelines for designing molecular bridging strategies at the buried interface of PSCs.

TiCl4precursor affecting the performance of HTM-free carbon-based perovskite solar cell.

The presence of TiO2used as an efficient electron transport layer is crucial to achieving high-performance solar cells, especially for a hole transport material (HTM)-free carbon-based perovskite solar cell (PSC). The hydrolysis of TiCl4is one of the most widely used routes for forming TiO2layer in solar cells, which includes the stock solution preparation from TiCl4initial precursor and the thermal hydrolysis of the stock solution. The second thermal hydrolysis step has been extensively studied, while the initial hydrolysis reaction in the first step is not receiving sufficient attention, especially for its influence on the photovoltaic performance of HTM-free carbon-based devices. In this study, the role of TiCl4stock solution in the growth process of TiO2layer is examined. Based on the analysis of the Ti(IV) intermediate states for different TiCl4concentrations from Raman spectra, 2 M TiCl4precursor exhibits moderate nucleation and growth kinetics without generating too many intermediates which occurs in 3 M TiCl4precursor, yielding ∼300 nm size spherical TiO2agglomerates with a rutile phase. In the aspect of devices, the HTM-free carbon-based PSCs fabricated using 2 M TiCl4precursor deliver a conversion efficiency beyond 17%, which may be attributed to the reduced defect in compact TiO2layer.

Lithiated Phosphoryl Cellulose Nanocrystals Enhance Cycling Stability and Safety of Quasi-Solid-State Lithium Metal Batteries.

Cycling stability and safety are two of the main challenges facing lithium metal batteries with metallic lithium as anodes. Quasi-solid-state lithium metal batteries based on gel polymer electrolytes are one of the important development directions for lithium metal batteries addressing those challenges. Herein, we prepare lithiated phosphoryl cellulose nanocrystals (PCNC-Li) as a modification material for poly(vinylidene fluoride) (PVDF) gel polymer electrolyte to improve cycling stability and safety of quasi-solid-state lithium metal batteries. The synthesized PCNC-Li tends to form a uniform network structure on the surface of the PVDF membrane, in which the phosphoryl groups grafted regularly on celluloses can regulate the transport of lithium ions. As a result, a more uniform ion flux and more stable lithium anode interface support an obviously improved cycling stability for lithium metal batteries. Moreover, the introduction of the PCNC-Li coating layer makes the modified PVDF membranes have a better thermal stability and an enhanced mechanical strength, which is beneficial for improvement of safety of lithium metal batteries. This work provides a new alternative to fabricating a better composite gel polymer electrolyte for lithium metal batteries.

Thermal tolerance of perovskite quantum dots dependent on A-site cation and surface ligand.

A detailed picture of temperature dependent behavior of CsxFA1-xPbI3 perovskite quantum dots across the composition range is constructed by performing in situ optical spectroscopic and structural measurements, supported by theoretical calculations that focus on the relation between A-site chemical composition and surface ligand binding. The thermal degradation mechanism depends not only on the exact chemical composition, but also on the ligand binding energy. The thermal degradation of Cs-rich perovskite quantum dots is induced by a phase transition from black γ-phase to yellow δ-phase, while FA-rich perovskite quantum dots with higher ligand binding energy directly decompose into PbI2. Quantum dot growth to form large bulk size grain is observed for all CsxFA1-xPbI3 perovskite quantum dots at elevated temperatures. In addition, FA-rich quantum dots possess stronger electron-longitudinal optical phonon coupling, suggesting that photogenerated excitons in FA-rich quantum dots have higher probability to be dissociated by phonon scattering compared to Cs-rich quantum dots.

Fast Charge-Transport Interface on Primary Particles Boosts High-Rate Performance of Li-Rich Mn-Based Cathode Materials.

A Li-rich Mn-based layered oxide cathode (LLO) is one of the most promising cathode materials for achieving high-energy lithium-ion batteries. Nevertheless, the intrinsic problems including sluggish kinetics, oxygen evolution, and structural degradation lead to unsatisfactory performance in rate capability, initial Coulombic efficiency, and stability of LLO. Herein, different from the current typical surface modification, an interfacial optimization of primary particles is proposed to improve the simultaneous transport of ions and electrons. The modified interfaces containing AlPO4 and carbon can effectively increase the Li+ diffusion coefficient and decrease the interfacial charge-transfer resistance, thereby achieving fast charge-transport kinetics. Moreover, the in situ high-temperature X-ray diffraction confirms that the modified interface can improve the thermal stability of LLO by inhibiting the lattice oxygen release on the surface of the delithiated cathode material. In addition, the chemical and visual analysis of the cathode-electrolyte interface (CEI) composition clarifies that a highly stable and conductive CEI film generated on the modified electrode can facilitate interfacial kinetic transmission during cycling. As a result, the optimized LLO cathode exhibits a high initial Coulombic efficiency of 87.3% at a 0.2C rate and maintains superior high-rate stability with a capacity retention of 88.2% after 300 cycles at a 5C high rate.

Dimensionally Stable Composite Li Electrode with Cu Skeleton and Lithophilic Li-Mg Alloy Microstructure.

Lithium electrodes have gained increasing attention in recent years for their promising applications in high-energy-density secondary batteries. However, structural instability during cycling remains a considerable obstacle to development. In this study, a dimensionally stable Li-Mg/Cu composite electrode was fabricated. Cu foam as a plate grid can sustain the structure, and Li-Mg alloy as the active and lithophilic component can guide the uniform Li plating within the composite. Thus, Li-Mg/Cu electrode shows long-term stability in terms of dimensional change and surface morphology. This work provides a facile and practical way to fabricate composite Li electrodes with high dimensional stability for secondary batteries.

Organo-Soluble Decanoic Acid-Modified Ni-Rich Cathode Material LiNi0.90Co0.07Mn0.03O2 for Lithium-Ion Batteries.

Ni-rich layered oxides as cathode materials deliver a higher capacity than those used currently, in hopes of improving the energy density of Li-ion batteries. However, the surface residual alkali and the interfacial parasitic reactions caused by the rich nickel bring a series of problems such as surface slurrying, structure deterioration, mechanical fracture, and capacity decay. Herein, different from the common surface coating strategies with inorganics, an organo-soluble acid modification approach is proposed to meet the challenges. For LiNi0.90Co0.07Mn0.03O2 (NCM90), decanoic acid can react with the residual lithium salts on the surface to form an organic lithium salt-dominant modification layer. During cycling, an organic lithium-involved cathode/electrolyte interface (CEI) layer is rapidly formed. Specially, the solubility of decanoic acid in the organic electrolyte makes the CEI layer keep strong interaction with NCM90, thin but effective. Consequently, the modified NCM90 exhibits notable performances in terms of structural stability, mechanical integrity, and capacity retention.

Ocular phenotype related SNP analysis in Southern Han Chinese population from Guangdong province.

Ocular phenotype is recognizable among Asians, including eyelid fold, fissure inclination, and canthal index. Here we screened 27 facial phenotype-associated SNPs and reported a preliminary study in 246 Chinese individuals of Han origin in Guangdong province. Results showed that rs17760296 could explain 6.2% of the eyelid fold variation and double eyelids were more likely to appear when one's genotype was TT. With respect to the canthal index, rs4791774 and rs642961 were significantly associated with it. However, no individual SNP was associated with fissure inclination. We further constructed two models to predict eyelid fold and canthal index and evaluated them with receiver operating characteristic (ROC) curves and support vector machine (SVM) regression, respectively. The models showed a moderate-to-high predictive capacity (AUC = 0.75, sensitivity = 76%, and specificity = 72%) for the eyelid fold while a mild performance (R2 = 0.1074, MSE = 0.0005, P-value = 0.024) for the canthal index. In conclusion, our study indicates that rs17760296 could be selected into the facial phenotype prediction system for the Southern Han Chinese population. More SNPs are encouraged to improve the prediction accuracy of the canthal index besides rs4791774 and rs642961.

La2MoO6 as an Effective Catalyst for the Cathode Reactions of Lithium-Sulfur Batteries.

Lithium-sulfur batteries with high theoretical energy density have emerged as one of the most promising next-generation rechargeable batteries, while their discharge capacity and cycle stability are challenges mainly due to the shuttle effect of polysulfide intermediates. Employing an effective catalyst for the conversion of polysulfides in cathode reactions can promote the reaction kinetics to restrain the shuttle of polysulfides. Here, for the first time, La2MoO6 (LMO) as a catalyst is introduced into sulfur cathodes. To investigate the effect of La2MoO6, we prepare two different structures of La2MoO6/carbon nanofiber composites. One is carbon nanofiber-supported crystalline La2MoO6 nanoparticles (LMO@CNFs) and the other is amorphous La2MoO6 nanoparticles embedded in carbon nanofibers (LMO-in-CNFs). For sulfur electrodes with ∼73 wt % sulfur loading, LMO@CNFs/S and LMO-in-CNFs/S deliver initial gravimetric capacities of 1493.4 and 1246.7 mA h g-1, respectively, at a 0.1C rate, obviously higher than that of the control sample CNFs/S. Moreover, LMO@CNFs/S shows much better rate performance than LMO-in-CNFs/S, indicating strongly that La2MoO6 is a highly effective catalyst to promote kinetic conversion of polysulfides.

Coupling aqueous zinc batteries and perovskite solar cells for simultaneous energy harvest, conversion and storage.

Simultaneously harvesting, converting and storing solar energy in a single device represents an ideal technological approach for the next generation of power sources. Herein, we propose a device consisting of an integrated carbon-based perovskite solar cell module capable of harvesting solar energy (and converting it into electricity) and a rechargeable aqueous zinc metal cell. The electrochemical energy storage cell utilizes heterostructural Co2P-CoP-NiCoO2 nanometric arrays and zinc metal as the cathode and anode, respectively, and shows a capacity retention of approximately 78% after 25000 cycles at 32 A/g. In particular, the battery cathode and perovskite material of the solar cell are combined in a sandwich joint electrode unit. As a result, the device delivers a specific power of 54 kW/kg and specific energy of 366 Wh/kg at 32 A/g and 2 A/g, respectively. Moreover, benefiting from its narrow voltage range (1.40-1.90 V), the device demonstrates an efficiency of approximately 6%, which is stable for 200 photocharge and discharge cycles.

Colloidal Quantum Dot Solar Cells: Progressive Deposition Techniques and Future Prospects on Large-Area Fabrication.

Colloidally grown nanosized semiconductors yield extremely high-quality optoelectronic materials. Many examples have pointed to near perfect photoluminescence quantum yields, allowing for technology-leading materials such as high purity color centers in display technology. Furthermore, because of high chemical yield, and improved understanding of the surfaces, these materials, particularly colloidal quantum dots (QDs) can also be ideal candidates for other optoelectronic applications. Given the urgent necessity toward carbon neutrality, electricity from solar photovoltaics will play a large role in the power generation sector. QDs are developed and shown dramatic improvements over the past 15 years as photoactive materials in photovoltaics with various innovative deposition properties which can lead to exceptionally low-cost and high-performance devices. Once the key issues related to charge transport in optically thick arrays are addressed, QD-based photovoltaic technology can become a better candidate for practical application. In this article, the authors show how the possibilities of different deposition techniques can bring QD-based solar cells to the industrial level and discuss the challenges for perovskite QD solar cells in particular, to achieve large-area fabrication for further advancing technology to solve pivotal energy and environmental issues.

High-Efficiency Hybrid Sulfur Cathode Based on Electroactive Niobium Tungsten Oxide and Conductive Carbon Nanotubes for All-Solid-State Lithium-Sulfur Batteries.

All-solid-state lithium-sulfur batteries (ASSLSBs) have become a promising candidate because of their high energy density and safety. To ensure the high utilization and electrochemical capacity of sulfur in all-solid-state batteries, both the electronic and ionic conductivities of the sulfur cathode should be as high as possible. In this work, an intercalation-conversion hybrid cathode is proposed by distributing sulfur evenly on electroactive niobium tungsten oxide (Nb18W16O93) and conductive carbon nanotubes (CNTs) for achieving high performance ASSLSBs. Herein, Nb18W16O93 shows good electrochemical lithium storage in the hybrid cathode, which could serve as an effective Li-ion/electron conductor for the conversion of sulfur in the discharge/charge processes to achieve a high utilization of sulfur. However, CNTs could further increase the electronic conductivity of the hybrid cathode by constructing good conductive frameworks and suppress the volumetric fluctuation during the interconversion of sulfur and Li2S. With this strategy, the S/Nb18W16O93/CNT cathode achieves a high sulfur utilization of 91% after one cycle activation with a high gravimetric capacity of 1526 mA h g-1. In addition, excellent rate performance is also obtained at 0.5 C with a reversible capacity of 1262 mA h g-1 after 1000 cycles. This work offers a new perspective to develop ASSLSBs.

Elucidating the Effect of the Dopant Ionic Radius on the Structure and Electrochemical Performance of Ni-Rich Layered Oxides for Lithium-Ion Batteries.

The merits of Ni-rich layered oxide cathodes in specific capacity and material cost accelerate their practical applications in electric vehicles and grid energy storage. However, detrimental structural deterioration occurs inevitably during long-term cycling, leading to potential instability and capacity decay of the cathodes. In this work, we investigate the effect of the doped cation radius on the electrochemical performance and structural stability of Ni-rich cathode materials by doping with Mg and Ca ions in LiNi0.8Co0.1Mn0.1O2. The results reveal that an increase in the doping ion radius can enlarge the interlayer spacing but lead to the collapse of the layered structure if the ion radius is too large, which undermines the cycling stability of the cathode material. Compared with the Ca-doped sample and the pristine material, Mg-doped LiNi0.8Co0.1Mn0.1O2 presents improved structural stability and superior thermal stability due to the pillar and glue roles of medium-sized Mg ions in the lithium layer. The results of this study suggest that a suitable ionic radius of the dopant is critical for stabilizing the structure and improving the electrochemical properties of Ni-rich layered oxide cathode materials.

Congener Substitution Reinforced Li7P2.9Sb0.1S10.75O0.25 Glass-Ceramic Electrolytes for All-Solid-State Lithium-Sulfur Batteries.

Glass-ceramic sulfide solid electrolytes like Li7P3S11 are practicable propellants for safe and high-performance all-solid-state lithium-sulfur batteries (ASSLSBs); however, the stability and conductivity issues remain unsatisfactory. Herein, we propose a congener substitution strategy to optimize Li7P3S11 as Li7P2.9Sb0.1S10.75O0.25 via chemical bond and structure regulation. Specifically, Li7P2.9Sb0.1S10.75O0.25 is obtained by a Sb2O5 dopant to achieve partial Sb/P and O/S substitution. Benefiting from the strengthened oxysulfide structural unit of POS33- and P2OS64- with bridging oxygen atoms and a distorted lattice configuration of the Sb-S tetrahedron, the Li7P2.9Sb0.1S10.75O0.25 electrolyte exhibits prominent chemical stability and high ionic conductivity. Besides the improved air stability, the ionic conductivity of Li7P2.9Sb0.1S10.75O0.25 could reach 1.61 × 10-3 S cm-1 at room temperature with a wide electrochemical window of up to 5 V (vs Li/Li+), as well as good stability against Li and Li-In alloy anodes. Consequently, the ASSLSB with the Li7P2.9Sb0.1S10.75O0.25 electrolyte shows high discharge capacities of 1374.4 mAh g-1 (0.05C, 50th cycle) at room temperature and 1365.4 mAh g-1 (0.1C, 100th cycle) at 60 °C. The battery also presents remarkable rate performance (1158.3 mAh g-1 at 1C) and high Coulombic efficiency (>99.8%). This work provides a feasible technical route for fabricating ASSLSBs.

To Promote the Catalytic Conversion of Polysulfides Using Ni-B Alloy Nanoparticles on Carbon Nanotube Microspheres under High Sulfur Loading and a Lean Electrolyte.

Despite their high theoretical energy density, the application of lithium-sulfur batteries is seriously hindered by the polysulfide shuttle and sluggish kinetics, especially with high sulfur loading and under low electrolyte usage. Herein, to facilitate the conversion of lithium polysulfides, nickel-boron (Ni-B) alloy nanoparticles, dispersed uniformly on carbon nanotube microspheres (CNTMs), are used as sulfur hosts for lithium-sulfur batteries. It is demonstrated that Ni-B alloy nanoparticles can not only anchor polysulfides through Ni-S and B-S interactions but also exhibit high electrocatalytic capability toward the conversion of intermediate polysulfide species. In addition, the intertwined CNT microspheres provide an additional conductive scaffold in response to the fast electrochemical redox. The enhanced redox kinetics is beneficial to improve the specific capacity and cycling stability of the sulfur cathode, based on the fast conversion of lithium polysulfides and effective deposition of the final sulfide products. Conclusively, the S/Ni-B/CNTM composite delivers a high specific capacity (1112.7 mAh gs-1) along with good cycle performance under both high sulfur loading (8.3 mg cm-2) and a lean electrolyte (3 µL mgs-1). Consequently, this study opens up a path to design new sulfur hosts toward lithium-sulfur batteries.

Two-Terminal Perovskite-Based Tandem Solar Cells for Energy Conversion and Storage.

The organic-inorganic hybrid perovskite solar cells present a rapid improvement on power conversion efficiency from 3.8% to 25.5% in the past decades. Owing to the tuneable bandgaps, low-cost, and ease of fabrication, perovskites become ideal candidate materials for fabricating tandem solar cells, especially for efficient and high-voltage monolithic two-terminal devices. In this review, an overview of recent advances in various monolithic perovskite-based tandem solar cells with a focus on the key challenges is provided. Subsequently, the recombination layer materials, construction of wide-bandgap perovskite layer, stability of narrow-bandgap, and current matching principle in tandems are highlighted in order to optimize the output voltage and conversion efficiency of tandem solar cells. Finally, the recent progress is summarized with a focus on potential applications of tandem solar cells for energy conversion and storage, including hydrogen production by water splitting, CO2 reduction, supercapacitors, and rechargeable batteries, benefiting from the adjustable output voltage of tandem solar cells. It is hoped that this work can offer a feasible strategy to explore more possibilities for fabricating new two-terminal tandem solar cells with high voltage and high conversion efficiency for energy conversion and storage.

Crystalline Multi-Metallic Compounds as Host Materials in Cathode for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) battery is one of the most promising next-generation rechargeable batteries. Lots of fundamental research has been done for the problems during cycling like capacity fading and columbic efficiency reducing owing to severe diffusion and migration of polysulfide intermediates. In the early stage, a wide variety of carbon materials are used as host materials for sulfur to enhance electrical conductivity and adsorb soluble polysulfides. Beyond carbon materials, metal based polar compounds are introduced as host materials for sulfur because of their strong catalytic activity and adsorption ability to suppress the shuttle effect. In addition, relatively high density of metal compounds is helpful for increasing volumetric energy density of Li-S batteries. This review focuses on crystalline multi-metal compounds as host materials in sulfur cathodes. The multi-metal compounds involve not only transition metal composite oxides with specific crystalline structures, binary metal chalcogenides, double or complex salts, but also the metal compounds doped or partially substituted by other metal ions. Generally, for the multi-metal compounds, microstructure and morphologies in micro-nano scale are very significant for mass transfer in electrodes; moreover, adsorption and catalytic ability for polysulfides make fast kinetics in the electrode processes.

Yttrium Surface Gradient Doping for Enhancing Structure and Thermal Stability of High-Ni Layered Oxide as Cathode for Li-Ion Batteries.

The high-nickel layered oxides are potential candidate cathode materials of next-generation high energy lithium-ion batteries, in which higher nickel/lower cobalt strategy is effective for increasing specific capacity and reducing cost of cathode. Unfortunately, the fast decay of capacity/potential, and serious thermal concern are critical obstacles for the commercialization of high-nickel oxides due to structural instability. Herein, in order to improve the structure and thermal stability of high-nickel layered oxides, we demonstrate a feasible and simple strategy of the surface gradient doping with yttrium, without forming the hard interface between coating layer and bulk. As expected, after introducing yttrium, the surface gradient doping layer is formed tightly based on the oxidation induced segregation, leading to improved structure and thermal stability. Correspondingly, the good capacity retention and potential stability are obtained for the yttrium-doped sample, together with the superior thermal behavior. The excellent electrochemical performance of the yttrium-doped sample is primarily attributed to the strong yttrium-oxygen bonding and stable oxygen framework on the surface layer. Therefore, the surface manipulating strategy with the surface gradient doping is feasible and effective for improving the structure and thermal stability, as well as the capacity/potential stability during cycling for the high-Ni layered oxides.

A p-p+ Homojunction-Enhanced Hole Transfer in Inverted Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) have triggered a research trend in solar energy devices in view of their high power conversion efficiency and ease of fabrication. However, more delicate strategies are still required to suppress carrier recombination at charge transfer interfaces, which is the necessary path to high-efficiency solar cells. Here, a p-p+ homojunction was constructed on basis of NiO film to enhance hole transfer in an inverted planar perovskite solar cell. The homojunction was generated by fabricating a NiO/Cu:NiO bilayer film. The density functional theory calculation demonstrated the charge density difference in the two layers, which could generate a space charge region and a band bending at the junction, and the result was further proved by energy level structure analysis of NiO and Cu:NiO films. The designed homojunction could accelerate the hole transfer and inhibit carrier recombination at the interface between hole transfer layer and perovskite layer. Finally, the inverted planar perovskite solar cell with p-p+ homojunction showed an efficiency of 18.30 % and a high fill factor of 0.81, which were much higher than the counterpart of the PSCs individually using NiO or Cu:NiO as hole transfer layer. This work developed a new structure of hole transport layer to enhance the performance of PSCs, and also provided new ideas for design of charge transfer films.

From Dendrites to Hemispheres: Changing Lithium Deposition by Highly Ordered Charge Transfer Channels.

Metallic lithium as an anode is an ultimate ideal for rechargeable lithium batteries with high energy density such as lithium-oxygen batteries and lithium-sulfur batteries. However, the excess reactivity and asymmetrical dissolution-deposition of the metallic lithium anode make it impossible to support a stable long charge-discharge cycling. To protect the metallic lithium anode, apparently it needs to adjust the dissolution and deposition of lithium ions, but more essentially, it should reasonably change the distribution and transport of electrons on the surface and interface of the metallic lithium. In this work, anodic aluminum oxide (AAO) membranes are used to build highly ordered channels on the lithium anode surface in which lithium ions can transfer in the channels and electrons can be transported by the lithiation reaction of alumina with an oxygen vacancy-involved process. As a result, the cyclic reaction actually is partially transferred to the AAO surface, and lithium deposition occurs there as a hemispherical appearance but not as dendrites. Meanwhile, the highly ordered characteristics provide a physical effect to make the deposited lithium hemispheres a uniform distribution on the AAO surface. The AAO-regulated lithium anodes could be widely used to improve the cycling performance for metal lithium batteries.