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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.

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-N

Semi-transparent organic photovoltaics (OPVs) are an emerging solar-energy-harvesting technology with promising applications, such as rooftop energy supplies for environmentally friendly greenhouses. However, the poor operational stability of OPVs poses challenges to their feasibility as incessantly serving facilities. Here we report a reductive interlayer structure for semi-transparent OPVs that improves the operational stability of OPVs under continuous solar radiation. The interlayer effectively suppresses the generation of radicals from the electron transport layer under sunlight and prevents the structural decomposition of the organic photoactive layer during operation. The defects that serve as the charge carrier recombination sites are nullified by the electron-donating functional groups of the reduced molecules, which improves photovoltaic performance. The semi-transparent OPVs demonstrate a power conversion efficiency of 13.5% and an average visible transmittance of 21.5%, with remarkable operational stability (84.8% retention after 1,008 h) under continuous illumination. Greenhouse results show that the semi-transparent OPV roof benefits the survival rate and growth of the crops, indicating the importance of our approach in addressing food and energy challenges.

In this article, we develop a continuous periodic switching model depicting Wolbachia infection frequency dynamics in mosquito populations by releasing Wolbachia-infected mosquitoes, which is different from the discrete modeling efforts in the literature. We obtain sufficient conditions on the existence of a unique and exactly two periodic solutions and analyze the stability of each periodic solution, respectively. We also provide a brief discussion and several numerical examples to illustrate our theoretical results.

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)

We describe highly efficient and stable bifacial perovskite solar cells incorporating carbon nanotube network films as a back contact enabling perovskite/CIS 4-terminal tandem solar cells to reach apower conversion efficiency of over 27%.

Precise control of the growth of 2D perovskites on 3D perovskites to form “trans-grain boundaries” 2D/3D structure for the preparation of flexible perovskite solar cells with a certified PCE up to 22.1% and excellent mechanical stability.

Glycolaldehyde, a C2 compound, is the simplest sugar molecule, but whether it inherently exists in plants remains unclear due to its complicated existence form in different reaction conditions.

Due to the lack of professional development time and awareness, well-directed training content, respect for teachers and value for education, the professional development of rural border elementary school teachers is a problem that needs to be solved urgently. The study suggests that the teaching faculty should be complemented and strengthened, the contents of teacher training should be “localized,” the internal drive of teachers should be stimulated, the respect for teachers and education should be promoted, thus improving the overall quality of the teaching faculty and promoting the balanced development of compulsory education.

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, (FAPbI

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.

Summary Although great progress is being made toward improving the power conversion efficiency (PCE) and the operational stability of perovskite solar cells (PSCs), little attention is being paid to their mechanical reliability, which is particularly important for flexible PSCs (f-PCSs). Here, we have grown low-dimensional (LD) metal-halide perovskite (MHP) thin capping layer over the 3D MHP light-absorber thin film in f-PSCs in situ to improve their mechanical reliability. This resulted in f-PSCs with unprecedented, simultaneous improvements in PCE (21.0%), operational stability (T90, retention of 90% of the initial PCE, >800 h), and bending durability (T80 = 20,000 tension-only bending cycles). These synergistic virtuous effects are attributed to the LD MHP capping layer enhancing photocarriers extraction, providing protection against the environment, and “sealing” surface flaws on the 3D MHP thin film. The latter reduces the propensity for cracking in bending, which results in improved environmental stability and bending durability.

Precisely controlled synthesis is one of the key issues for single-atom catalysts (SACs) due to isolated atoms have high surface-free-energy toward aggregation. Here, we propose a facile cooperativ...

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.

Currently, pyrolysis as the most widely used method still has some key issues not well resolved for synthesis of carbon-supported single-atom catalysts (C-SACs), e.g., the sintering of metal atoms at high temperature as well as the high cost and complicated preparations of precursors. In this report, molten salts are demonstrated to be marvellous medium for preparation of C-SACs by pyrolysis of small molecular precursors (ionic liquid). The ultrastrong polarity on one hand establishes robust interaction with precursor and enables better carbonization, resulting in largely enhanced yield. On the other hand, the aggregation of metal atoms is effectively refrained while no nanoparticle or cluster is formed. By this strategy, a C-SAC with atomically dispersed Fe-N4 sites and a high specific area over 2000 m2 g−1 is obtained, which illustrates high ORR activity in both acid and alkaline media. Moreover, this SAC exhibits superior methanol tolerance and stability after acid soaking at 85 °C for 48 h. It is believed that the molten-salts-assisted pyrolysis can be developed into a routine strategy as it not only can largely simply the synthesis of C-SACs, but also can be extended to prepare other types of SACs.

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., Operational stability and mechanical robustness remain as engineering bottlenecks in perovskite solar cells technology. Here, Dong et al. introduce an interpenetrating perovskite at the electron-transporting-layer interface that enables a 1000-hour stable operation and high endurance against bending fatigue over 2500 cycles.

Due to their outstanding advantages like excellent moisture resistance and compatibility with up-scalable manufacturing processes, carbon (C) electrode hole transport layer (HTL)-free perovskite solar cells (PSCs) represent an excellent solution to the serious limitations caused by the commonly used HTL and expensive noble metal electrode. The C-electrode can be deposited using different techniques from various carbon allotropes and their derivatives. However, the choice of optimal carbon sources is still open to debate, which will certainly have a strong effect on the performance and long-term stability of the resulting PSCs. Here, the modular HTL-free C-PSCs were assembled by the lamination of two independently processed half-stacks of a semi-cell and a charge collector, where the C-electrodes were processed using a simple spray coating technique at low temperature (85 °C). Three typical carbon sources were used, i.e., multiwall carbon nanotube (MWCNT), carbon nanocoil (CNC), and graphene. A comparative study was conducted to determine the best candidate. Results indicated that MWCNT might be more preferable as the back electrode in HTL-free PSCs in terms of well-aligned band alignment, superior ability in extraction and collection of photo-generated holes. As a result, an improved power conversion efficiency (PCE) of 11.2% was achieved for modular MWCNT-based PSCs, and much improved thermal and humidity stabilities were also demonstrated. Our achievement demonstrates the irreplaceable role of tri-functional MWCNT in C-based HTL-free PSCs with integrated function: (i) back electrode; (ii) hole extraction and collection; and (iii) excellent moisture barrier.

Carbon-based single-atom catalysts (C-SACs), featured with flexible, well-defined atomic geometry and superior electrical conductivity, have experienced a rapid development in the last decade and proved unique opportunities in selective oxygen reduction reaction (ORR) electrocatalysis via direct 4e- pathway or alternative 2e- pathway for sustainable energy conversion and chemical synthesis. This concise review summarizes recent experimental efforts aiming at tailored selectivity, activities and derived progressive guidelines for catalyst design. First, the current exploration and development of synthetic methodologies of diverse C-SACs for ORR is briefly outlined. Then we present a key overview on structure-dependent catalytic selectivity and activity properties, in particular emphasizing on the microenvironment modulation of single-atom active sites from the aspects of regulating the central metal atoms, coordination environment and support properties. Besides, the dual active sites enabled synergistic catalysis for breaking conventional scaling relation are also highlighted. Finally, the current remaining challenges in C-SACs for ORR and related perspectives are proposed to shed some light on the further developments toward industrialization in the future.

Glycolaldehyde (HOCH2CHO, GA), the simplest molecule containing both hydroxyl and aldehyde groups, is structurally the most elementary member of monosaccharide sugars, which may provide new clues for probing the origin of life on planets like the Earth. Uncovering the existing state of GA in solution systems is an important scientific issue. Generally, methanol is used as the main mobile phase in the liquid chromatography analysis of GA, but the state of GA existing in methanol solution remains unknown, thus making it difficult to analyse GA accurately. Herein, the state and dynamic equilibrium of GA in methanol solution were systematically studied by UV-visible spectroscopy, nuclear magnetic resonance (1H-NMR) spectroscopy, liquid chromatography mass spectrometry (LC–MS) and density functional theory (DFT) calculations. The results demonstrated that the equilibrium component of GA in methanol solution is different from that in aqueous solution and that glycolaldehyde hemiacetal (GAHA) is a dominant component (>90%). Laying the foundation for experimental analysis, the transformation of different components at equilibrium was studied using DFT. The results confirm that hydrogen bonding-induced proton transfer occurs between the components at equilibrium. This work provides an important reference for the analysis of sugars and related compounds in various biochemical reactions.

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.

Carbon-supported single-atom catalysts (C-SACs) are promising candidates for numerous electrocatalysis reactions. However, the controllable and economical synthesis of C-SACs remains a challenge since most of the examples were synthesized via multi-procedures and required elaborate selection of precursors, as well as severe sintering of the metal atoms as well. Herein, through high temperature carbonization in molten salts, we for the first time demonstrate a facile and low-cost strategy for the direct transformation of raw biomass into porous C-SACs with well-defined Fe–N4 sites (termed as Fe–N/C-SAC). The high polarity of molten salts mentioned above can provide a unique environment in which the aggregation of metal atoms is strictly restricted, and instead they are trapped by N atoms from the precursor of pig liver, a cheap raw biomass containing abundant proteins. As an ORR catalyst in an alkaline medium, Fe–N/C-SAC not only exhibits a considerable onset potential (Eonset = 0.89 V vs. RHE) but also gives a high limiting current density (5.64 mA cm−2 at 0.6 V), which is comparable to that of commercial Pt/C (5.80 mA cm−2). In addition, this C-SACs also illustrate excellent stability and methanol tolerance.

Converting CO2 to carbon-containing fuels is an effective approach to relieving energy shortages. Carbon quantum dots (CQDs) have shown distinct properties and attracted tremendous interest in CO2 reduction. Herein, we report a joint experimental-computational mechanistic study of photoreduction CO2 to CO on the model catalyst 9-hydroxyphenal-1-one (HPHN) CQDs with known structure. Our theoretical calculations reveal that the rate-determining step is COOH∙ formation, which is closely related to the proton and electron transfer induced by hydrogen bonding in the excited state. According to the calculated volcano plot, the solution we proposed is addition Zn2+ ions. The active center changed from the hydroxyl oxygen atom to the Zn atom and the barrier of the COOH∙ formation step is noticeably decreased when Zn2+ ions are added. It is further confirmed by the experimental data that the activity of CO2 reduction increases 2.9 times when Zn2+ ions are added.

Perovskite solar cells (PSCs) as an emerging photovoltaic technique have achieved exceptional power conversion efficiency (PCE) up to 25.7% after fast development over the past decade. But currently some critical issues are still not well addressed in terms of realizing large-scale fabrication, for example, fast fabrication of high-quality perovskite film with good stability. Here, we demonstrate the use of stable and fast-crystallizing low-dimensional (LD) perovskite thin films as the light absorber with only a 10 s annealing time at 250 degrees C, delivering a PCE of 18.16%. The crystallization and photoelectric properties of LD perovskite are well illustrated. The reduction in the annealing time will dramatically increase the productivity of PSCs. The PSCs based on rapidly annealed LD perovskite thin films exhibit excellent stability, with only 12% loss of PCE after 1000 h storage at 85 degrees C and 40-70% relative humidity.

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 (

Art is a very practical activity, especially music art. Quality music education at colleges and universities is vital for the ideological and moral schooling of students. Owing to the rapid expansion of music education at graduate level, the building of therapeutic evaluation of music instruction is critical. In fact, most of the music instruction in colleges and universities has not built a scientific and appropriate evaluation system based on the actual teaching quality of the classroom. This work combines the emerging neural network (NN) technology with standard method of music teaching evaluation and proposes a novel method—Music Teaching Quality Evaluation Network (MTQEN). To effectively improve performance of the model, the method uses a one-dimensional convolutional neural network (1D-CNN) being optimized from three aspects: expanding the receptive field, reducing training parameters, and enhancing operationality. Instead of the traditional convolution layer, the dilated convolution layer is utilized to increase scope of local receptive field and to improve the feature extraction efficacy. To improve training rate and to eliminate dependency on batch size, the filter response normalization (FRN) is used. Moreover, global pooling is used to reduce the requisite training parameters and to improve the training efficiency. Results of the evaluation show that performance of MTQEN in term accuracy (95.6%) and recall (93.3%) is better than the other contemporary models. The method proposed has great significance in pedagogy of music and arts, whereas the network designed may be enhanced to effectively evaluate teaching in related domains as well.

In this work, we investigate the existence and stability of periodic orbits of a mosquito population suppression model based on sterile mosquitoes. The model switches between two sub-equations as the actual number of sterile mosquitoes in the wild is assumed to take two constant values alternately. Employing the Poincaré map method, we show that the model has at most two T-periodic solutions when the release amount is not sufficient to eradicate the wild mosquitoes, and then obtain some sufficient conditions for the model to admit a unique or exactly two T-periodic solutions. In particular, we observe that the model displays bistability when it admits exactly two T-periodic solutions: the origin and the larger periodic solution are asymptotically stable, and the smaller periodic solution is unstable. Finally, we give two numerical examples to support our lemmas and theorems.

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.

With the rapidly increasing development in photovoltaics, perovskite solar cells (PSCs) have become a star in this field. The intrinsic characteristics of perovskites have been deeply researched, b...

Tin-based halide perovskite solar cells (PSCs) hold the most promise among lead-free PSCs, but they are plagued with inadequate environmental stability and power-conversion efficiency (PCE). Here w...

Amorphous NbOx electron transport layer (ETL) shows great potential for boosting the power conversion efficiency (PCE) of perovskite solar cells (PSCs) at low temperatures (