Diffusion-Controlled Crystal Engineering with Diverse Antisolvent Intervention for the Preparation of High-Quality Hybrid Perovskite Films.

Antisolvent engineering is routinely used to modulate the crystallization of perovskite films as they can offer an additional driving force for nucleation. Actually, the intervention of antisolvent into nucleation is thought to involve some relatively fast and complex processes, which, however, are not fully understood so far. Here, the diffusion of the organic amine cation FA+ (one dominated precursor) and its distribution in a spin-coating process in different antisolvents is simulated by the computational fluid dynamics (CFD) model. It is suggested that a moderate diffusion rate (like that in the case of toluene as an antisolvent) not only enables to form a very uniform distribution of FA+ ions on the substrate, beneficial to the uniform nucleation of the intermediate phase, but also can balance the nucleation and growth rates of the intermediate phase, thereby suppressing undesired heterogeneous nucleation and growth. Results show that the perovskite film fabricated using toluene as an antisolvent has a high quality, based on which higher power conversion efficiencies of up to 24.32% are achieved for perovskite solar cells.

Uncovering Dynamic Edge-Sites in Atomic Co-N-C Electrocatalyst for Selective Hydrogen Peroxide Production.

Understanding the nature of single-atom catalytic sites and identifying their spectroscopic fingerprints are essential prerequisites for the rational design of target catalysts. Here, we apply correlated in situ X-ray absorption and infrared spectroscopy to probe the edge-site-specific chemistry of Co-N-C electrocatalyst during the oxygen reduction reaction (ORR) operation. The unique edge-hosted architecture affords single-atom Co site remarkable structural flexibility with adapted dynamic oxo adsorption and valence state shuttling between Co(2-δ)+ and Co2+ , in contrast to the rigid in-plane embedded Co1 -Nx counterpart. Theoretical calculations demonstrate that the synergistic interplay of in situ reconstructed Co1 -N2 -oxo with peripheral oxygen groups gives a rise to the near-optimal adsorption of *OOH intermediate and substantially increases the activation barrier for its dissociation, accounting for a robust acidic ORR activity and 2e- selectivity for H2 O2 production.

Rational Selection of the Lewis Base Molecules Targeted for Lead-Based Defects of Perovskite Solar Cells: The Synergetic Co-passivation of Carbonyl and Carboxyl Groups.

Defect passivation through Lewis acid-base chemistry has recently attracted significant interest because of its proven ability to improve the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). However, tedious trial-and-error procedures are commonly used for the selection of Lewis molecules due to their abundant variety. Herein, two typical Lewis base molecules, the M molecule containing only carbonyl groups and the 3M molecule containing both carbonyl and carboxyl groups, are proposed to passivate the Pb-based defects and mitigate their negative impacts on PSC performance. The results indicated that much stronger coordination bonds can be formed between the 3M molecule and uncoordinated Pb2+ than with the M molecule. Because of the benefit from the synergetic co-passivation effect of carbonyl and carboxyl groups, an impressive maximum PCE of 24.07% was achieved via 3M modification. More importantly, the modified devices demonstrated remarkably improved operational stability.

CD73/NT5E is a Potential Biomarker for Cancer Prognosis and Immunotherapy for Multiple Types of Cancers.

Cluster of Differentiations 73 (CD73)/ecto-5'-nucleotidase (NT5E) is a novel type of immune molecular marker expressed on many tumor cells and involved in regulating the essential immune functions and affecting the prognosis of cancer patients. However, it is not clear how the NT5E is linked to the infiltration levels of the immune cells in pan-cancer patients and their final prognosis. This study explores the role of NT5E in 33 tumor types using GEPIA, TIMER, Oncomine, BioGPS databases, and several bioinformatic tools. The findings reveal that the NT5E is abnormally expressed in a majority of the types of cancers and can be used for determining the prognosis prediction ability of different cancers. Moreover, NT5E is significantly related to the infiltration status of numerous immune cells, immune-activated pathways, and immunoregulator expressions. Last, specific inhibitor molecules, like NORNICOTINE, AS-703026, and FOSTAMATINIB, which inhibit the expression of NT5E in various types of cancers, are screened with the CMap. Thus, it is proposed that NT5E can be utilized as a potential biomarker for predicting the prognosis of cancer patients and determining the infiltration of various immune cells in different types of cancers.

In-Situ Grafting of Single-Atomic Titanium-Nitrogen Moiety onto Carbon Nanostructures for Efficient Photovoltaic Devices.

Early transition metals offer promising orthogonal reactivity to catalytic processes promoted by late transition metals. Nevertheless, exploiting variable single-atomic configurations as reactive centers is hitherto not well documented owing to their oxophilic nature. Herein we report an in-situ grafting strategy that employs nitrogenated holey carbon nitrides as a scaffold and invokes the reasonably good match of temperature-dependent pyrolysis to stabilize an atomic titanium-nitrogen (Ti1N2OH) moiety onto the hierarchical porous carbon support (Ti1/NC-SAC). The Ti1/NC-SAC as the cathode in dye-sensitized solar cells assembly exhibited superior electrocatalytic activity toward the triiodine reduction reaction, comparable to the conventional Pt cathode. DFT studies theoretically identified that the intrinsic robust triiodine reduction activity is essentially governed by the unique edge-hosted Ti sites, from both aspects, near-optimal adsorption of I intermediate and electron-donating ability. This work sheds light on the rational design of Ti-based SACs and their applications in photovoltaic fields.

Suppressing ion migration in metal halide perovskite via interstitial doping with a trace amount of multivalent cations.

Cations with suitable sizes to occupy an interstitial site of perovskite crystals have been widely used to inhibit ion migration and promote the performance and stability of perovskite optoelectronics. However, such interstitial doping inevitably leads to lattice microstrain that impairs the long-range ordering and stability of the crystals, causing a sacrificial trade-off. Here, we unravel the evident influence of the valence states of the interstitial cations on their efficacy to suppress the ion migration. Incorporation of a trivalent neodymium cation (Nd3+) effectively mitigates the ion migration in the perovskite lattice with a reduced dosage (0.08%) compared to a widely used monovalent cation dopant (Na+, 0.45%). The photovoltaic performances and operational stability of the prototypical perovskite solar cells are enhanced with a trace amount of Nd3+ doping while minimizing the sacrificial trade-off.

Synergistically Enhanced Single-Atom Nickel Catalysis for Alkaline Hydrogen Evolution Reaction.

The feature endowing atomic Ni-N-C electrocatalysts with exceptional intrinsic alkaline hydrogen evolution activity is hitherto not well-documented and remains elusive. To this end, we rationally exploited the hierarchical porous carbon microstructures as scaffolds to construct unique Ni-N2+2-S active sites to boost the sluggish Volmer reaction kinetics. Density functional theory reveals an obvious d-band center (ϵd) upshift of the edge-hosted Ni-N2+2-S sites compared with pristine Ni-N4, which translates to a more stabilized OH adsorption. Moreover, the synergetic dual-site (Ni and S atom) interplay gives rise to a decoupled regulation of the adsorption strength of intermediate species (OHad, Had) and thereby energetic water dissociation kinetics. Bearing these in mind, sodium thiosulfate was deliberately adopted as an additive in the molten salt system for controllable synthesis, considering the simultaneous catalyst morphology and active-site modulation. The target Ni-N2+2-S catalyst delivers a low working overpotential (83 mV@10 mA cm-2) and Tafel slope (100.5 mV dec-1) comparable to those of representative transition metal-based electrodes in alkaline media. The present study provides insights into the metal active-site geometry and promising synergistic effects over single-atom catalysis.

Imaging the Moisture-Induced Degradation Process of 2D Organolead Halide Perovskites.

Two-dimensional (2D) and quasi-2D Ruddlesden-Popper (RP) phase organolead halide perovskites are promising materials for both photovoltaic and optoelectronic devices. Although they are known to be more stable when exposed to moisture than their 3D counterpart, chemical degradation of these materials under moisture, which not only leads to a significant drop in device performance but also leads to lead leakage, yet remains one of the most serious hurdles for their practical applications. To gain insight into the degradation mechanism of 2D/quasi-2D perovskites under moisture conditions, the degradation pathway of 2D/quasi-2D (PEA)2(MA) n-1PbnI3n+1 (PEA = C6H5C2H4NH3 +, MA = CH3NH3 +, and n is the number of perovskite layers between adjacent organic spacer layers) perovskite single crystals (SCs) and thin film are explored. We observe the degradation process by mapping the photoluminescence of the 2D perovskites and demonstrate that the larger-n phases all directly degrade into the relative stable n = 1 phase and MAI and PbI2, which is a mechanism different from that in previous reports and further confirmed in the 2D perovskite thin film. This degradation process is also found to be independent of the boundary and morphology of the SCs. This discovery provides a new perspective for understanding the chemical degradation of the 2D perovskite materials and may inspire new solutions for improving their moisture stability.

Accelerating Photogenerated Hole Tunneling through Passivation Layers via Reducing Interplanar Spacing for Efficient and Stable Perovskite Solar Cells.

Interfacial passivation engineering plays a crucial role in the explosive development of perovskite solar cells (PSCs). However, previous studies on passivation layers mainly focused on the defect-passivation mechanism rather than the interfacial charge transport efficiency. Here, by precisely tuning the interplanar spacing of the ammonium iodide passivation layer, we elucidate the promoting effect of the reduced interplanar spacing of the passivation layer on the photogenerated hole tunneling efficiency at the interface of the hole transport layer and perovskite. Compared with the commonly used phenethylammonium iodide passivation layer with a wider interplanar spacing, 2-chlorobenzylammonium iodide with a narrower interplanar spacing can help break through the thickness limitation of the passivation layer, thus showing a better comprehensive passivation effect. Therefore, we demonstrate photovoltaic devices with an enhanced fill factor (FF) and open-circuit voltage (VOC), which yield a high power conversion efficiency (PCE) of up to 23.1%. We thus identify an efficient scheme to achieve optimal passivation conditions for high-performance PSCs.

Discrete dynamical models on Wolbachia infection frequency in mosquito populations with biased release ratios.

We develop two discrete models to study how supplemental releases affect the Wolbachia spreading dynamics in cage mosquito populations. The first model focuses on the case when only infected males are released at each generation. This release strategy has been proved to be capable of speeding up the Wolbachia persistence by suppressing the compatible matings between uninfected individuals. The second model targets the case when only infected females are released at each generation. For both models, detailed model formulation, enumeration of the positive equilibria and their stability analysis are provided. Theoretical results show that the two models can generate bistable dynamics when there are three positive equilibrium points, semi-stable dynamics for the case of two positive equilibrium points. And when the positive equilibrium point is unique, it is globally asymptotically stable. Some numerical simulations are offered to get helpful implications on the design of the release strategy.

Efficient Planar Perovskite Solar Cells with Carbon Quantum Dot-Modified spiro-MeOTAD as a Composite Hole Transport Layer.

In perovskite solar cells (PSCs), the hole-transport layer (HTL) plays an essential role in effective charge transport and extraction from the photoexcited perovskite, thus being significant for overall power conversion efficiency (PCE) and operational stability. So far, spiro-MeOTAD has been the most widely used HTL despite its inherent drawbacks, such as highly hygroscopic nature, poor conductivity, and mismatched energy-level alignment with the perovskite active layer. Here, a spiro-MeOTAD-based composite HTL modified by microwave method-synthesized carbon quantum dots (CQDs) was proposed and demonstrated as a promising HTL candidate for high-performance PSCs. The results demonstrated that the CQDs/spiro-MeOTAD composite HTL possesses several appealing characteristics for PSC applications, such as suitable energy levels for hole extraction, passivated interfacial trap states, and reduced recombination losses. Consequently, as compared to the control one using an unmodified spiro-MeOTAD HTL, (FAPbI3)0.95(MAPbBr3)0.05-based planar PSCs with composite HTL exhibit notably enhanced PCE and operational stability. Remarkably, an encouraging PCE of 20.41% was achieved for the champion device, and much improved operational stability was also demonstrated under continuous AM1.5 illumination with maximum power point (MPP) tracking conditions.

Unsupported Nanoporous Platinum-Iron Bimetallic Catalyst for the Chemoselective Hydrogenation of Halonitrobenzenes to Haloanilines.

An unsupported nanoporous platinum-iron bimetallic catalyst (PtFeNPore) was prepared with an electrochemical dealloying technique. Its structure and composition were characterized through various measurement methods, such as X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS). An intermetallic compound and iron oxide species were both found in the PtFeNPore catalyst. The nanoporous structure and Lewis acidity (caused by iron oxide species) of the PtFeNPore catalyst resulted in superior catalytic activity and high selectivity. The PtFeNPore-catalyzed hydrogenation of various halonitrobenzenes proceeded successfully under mild reaction conditions and produced good to excellent yields of the corresponding haloanilines with high selectivity. PtFeNPore can be recycled through magnetic separation easily and reused five times without significant deactivation.

Single-atom-catalyst with abundant Co-S4 sites for use as a counter electrode in photovoltaics.

Herein, a 7.35 wt% Co loading C-SAC is synthesized by pyrolysis of Co-MOF-74 in a strongly polar molten salt system. In dye-sensitized solar cells, this SAC based counter electrode shows higher photoelectric conversion efficiency than the Pt counter electrode. This work provides new insights for the preparation and application of C-SACs.

An insight into the reaction mechanism of CO2 photoreduction catalyzed by atomically dispersed Fe atoms supported on graphitic carbon nitride.

We report a combination of experimental and computational mechanistic studies for the photoreduction of CO2 to CO with water, catalyzed by single-atom Fe supported on graphitic carbon nitride (g-C3N4). Density functional theory (DFT) and time-dependent DFT (TDDFT) methods were utilized to explore the behavior of single-atom Fe in g-C3N4, which is of vital importance to the understanding of the CO2 reduction reaction (CO2RR) mechanism. The calculation results reveal that the rate-limiting step of the hydrogen-bonded complex in the absence of Fe atoms is the cleavage of C-O bonds in COOH radicals during the whole CO2RR, which includes the photophysical and photochemical processes. The presence of Fe atoms not only activated CO2 in the ground state and increased the rate constant of the limiting step in the photophysical process, but also functioned as the catalytic active center, lowering the reaction barrier of the C-O bond cleavage in COOH˙ in the photochemical process and resulting in improved photocatalytic activity. In addition, DFT calculations further demonstrated that the electron and proton transfer involved in the photophysical and photochemical processes is closely related to and induced by the hydrogen bonds in the excited state.

Interpenetrating interfaces for efficient perovskite solar cells with high operational stability and mechanical robustness.

The perovskite solar cell has emerged rapidly in the field of photovoltaics as it combines the merits of low cost, high efficiency, and excellent mechanical flexibility for versatile applications. However, there are significant concerns regarding its operational stability and mechanical robustness. Most of the previously reported approaches to address these concerns entail separate engineering of perovskite and charge-transporting layers. Herein we present a holistic design of perovskite and charge-transporting layers by synthesizing an interpenetrating perovskite/electron-transporting-layer interface. This interface is reaction-formed between a tin dioxide layer containing excess organic halide and a perovskite layer containing excess lead halide. Perovskite solar cells with such interfaces deliver efficiencies up to 22.2% and 20.1% for rigid and flexible versions, respectively. Long-term (1000 h) operational stability is demonstrated and the flexible devices show high endurance against mechanical-bending (2500 cycles) fatigue. Mechanistic insights into the relationship between the interpenetrating interface structure and performance enhancement are provided based on comprehensive, advanced, microscopic characterizations. This study highlights interface integrity as an important factor for designing efficient, operationally-stable, and mechanically-robust solar cells.

Salt melt synthesis of Chlorella-derived nitrogen-doped porous carbon with atomically dispersed CoN4 sites for efficient oxygen reduction reaction.

Carbon-supported single-atom catalysts (C-SACs) demonstrate great potential in various key electrochemical reactions. Nevertheless, the development of facile and economical strategies is highly appealing yet challenging given that the commonly used pyrolysis method has strict requirements on the structure and composition of precursors. Here, we demonstrate for the first time a facile and low-cost pyrolysis strategy assisted by molten salts at high temperature for preparing porous C-SACs with well-dispersed Co-N4 sites directly from a Chlorella precursor. Based on the X-ray absorption fine structure results and aberration-corrected scanning transmission electron microscopy images, we show that single atom Co-N4 moieties are anchored on a carbon matrix. A porous structure with a large specific surface area (2907 m2 g-1) and atomically dispersed active sites of Co provide the as-prepared Co-N/C-SAC with excellent electrocatalytic activity and stability for the ORR. The electrochemical measurements show that the half-wave potential and limited current density of this material are 0.83 V vs. RHE and 5.5 mA cm-2, respectively, which are comparable to those of commercial Pt/C.

Enhancing the Interface Contact of Stacking Perovskite Solar Cells with Hexamethylenediammonium Diiodide-Modified PEDOT:PSS as an Electrode.

As an indispensable component of perovskite solar cells (PSCs), the commonly used Au and Ag electrodes still have some problems such as high cost and instability issues with regard to being corroded by iodide ions. In this paper, we report stacking perovskite solar cells (S-PSCs), which can avoid the use of precious metal electrodes and reduce the cost of devices and the requirements of equipment compared to conventional PSCs. The S-PSCs are composed of two semicells: a photoanode and a counter electrode (CE). For stacked devices, effective contact of the photoanode/CE interface is very important to the performance of the device. We used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the electrode and modified it by hexamethylenediammonium diiodide (HDADI2) to improve its physical and electrical properties. The surface of the HDADI2-modified PEDOT:PSS becomes rough and achieves higher adhesion, which enables the photoanode and CE to be sufficiently connected. In addition, the energy-level structure of the HDADI2-modified PEDOT:PSS matches better with that of the adjacent functional layers. Therefore, the S-PSCs performance has been significantly improved. Under an illumination area of 1 cm2, the power-conversion efficiency (PCE) of the S-PSCs can reach 15.21%. Moreover, the S-PSCs can be disassembled and assembled flexibly and repeatedly disassembled 500 times with almost no change in the PCE. This has a positive impact on cell maintenance and modular production.

Wolbachia infection enhancing and decaying domains in mosquito population based on discrete models.

In this article, we formulate and study a discrete equation model depicting the pattern of Wolbachia infection in a mosquito population. A domain in [Formula: see text] is called a Wolbachia infection enhancing (or decaying) domain if in which the Wolbachia infection frequency of the next generation is always bigger (or smaller) than that of the current generation. We first give a complete analysis of the equivalent Wolbachia infection frequency curves. And then we clearly characterize the Wolbachia infection enhancing domain and decaying domain for all of the parameters, respectively. Finally, some numerical examples are also provided to illustrate our theoretical results.

A Novel Single-Atom Electrocatalyst Ti1 /rGO for Efficient Cathodic Reduction in Hybrid Photovoltaics.

Single-atom catalysts (SACs) are a frontier research topic in the catalysis community. Carbon materials decorated with atomically dispersed Ti are theoretically predicted with many attractive applications. However, such material has not been achieved so far. Herein, a Ti-based SAC, consisting of isolated Ti anchored by oxygen atoms on reduced graphene oxide (rGO) (termed as Ti1 /rGO), is successfully synthesized. The structure of Ti1 /rGO is characterized by high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy, being determined to have a five coordinated local structure TiO5 . When serving as non-Pt cathode material in dye-sensitized solar cells (DSCs), Ti1 /rGO exhibits high electrocatalytic activity toward the tri-iodide reduction reaction. The power conversion efficiency of DSCs based on Ti1 /rGO is comparable to that using conventional Pt cathode. The unique structure of TiO5 moieties and the crucial role of atomically dispersed Ti in Ti1 /rGO are well understood by experiments and density functional theory calculations. This emerging material shows potential applications in energy conversion and storage devices.

Ozone-Mediated Controllable Hydrolysis for a High-Quality Amorphous NbOx Electron Transport Layer in Efficient Perovskite Solar Cells.

Amorphous NbOx electron transport layer (ETL) shows great potential for boosting the power conversion efficiency (PCE) of perovskite solar cells (PSCs) at low temperatures (<100 °C). To date, it is still a challenge to simultaneously control the hydrolysis of the NbOx precursor solution and reduce the impurities of NbOx ETLs during low-temperature solution processing under ambient conditions. Herein, for the first time, we report ozone (O3) as a strong ligand to stabilize Nb salt solutions under ambient conditions. The above procedure not only enables the formation of a highly repeatable amorphous NbOx film by suppressing the hydrolysis of the solution but also reduces the OH content in the film, which decreases the defect intensity and improves the conductivity of the NbOx ETL. Thus, the formation of highly repeatable NbOx ETL-based PSCs are obtained; moreover, these PSCs have high PCE values of 19.54 and 16.42% on rigid and flexible substrates, respectively, much higher than the devices based on ETLs from a solution without an O3 treatment.