Defect Passivation and Lithium Ion Coordination Via Hole Transporting Layer Modification for High Performance Inorganic Perovskite Solar Cells.

Metal halide inorganic perovskite solar cells (PSCs) have great potential to achieve high efficiency with excellent thermal stability. However, the surface defect traps restrain the achievement of high open circuit voltage (VOC ) and power conversion efficiency (PCE) of the devices due to the severe nonradiative charge recombination. Moreover, the state-of-the-art hole transporting layer (HTL) significantly hampers device moisture stability, even though it renders the highest solar cell efficiency. Herein, a one-stone-two-birds strategy is proposed using a biocompatible material tryptamine (TA) as an additive in HTL. First, TA bearing electron rich moieties can favorably passivate the surface defects of inorganic perovskite films, significantly reducing trap density and prolonging charge lifetime. It results in a drastic improvement of VOC from 1.192 to 1.251 V, with a VOC loss of 0.48 V. The corresponding PSCs achieve a 21.8% PCE under 100 mW cm-2 illumination. Second, TA in HTL can coordinate with lithium cations, retarding their reaction with moisture and increasing the moisture stability of HTL. Consequently, the black phase of inorganic perovskite films is well preserved, and the corresponding PSCs maintain 90% of the initial PCE after 800 h storage at relative humidity of 25-35%, much higher than the control devices.

Lake shrinkage-induced terrestrial ecological environmental quality degradation in a semiarid lake basin.

Lake water environmental problems caused by lake shrinkage in semiarid zones have attracted widespread attention, but few studies have quantified the impact of lake shrinkage on the terrestrial ecological environmental quality of watersheds. In this study, remote sensing image inversion, digital elevation modeling, and statistical analysis were applied to explore the impact of Lake Daihai shrinkage on the terrestrial ecological environmental quality of its receding water areas from 1986 to 2019. The results showed that the area of Lake Daihai shrank from 170.7 km2 in 1961 to 50.67 km2 in 2019, a shrinkage of 70.32%. The average annual shrinkage was 2.07 km2 during the period of 1986-2019 (r = -0.99, p < 0.01). The main conclusions of this study are as follows: The mean remote sensing ecological index values decreased significantly from 0.628 in 1986 to 0.441 in 2019 (r = -0.78, p < 0.05), which means that the terrestrial ecological environmental quality of the water receding area degraded from a good grade to a moderate grade. The increase in water use by residents in the basin was an important reason for the shrinkage of Lake Dahai. Approximately 90% of the wetlands in the receding water areas formed after the shrinkage of Lake Daihai were converted to farmland by local residents, which significantly degraded the terrestrial ecological environmental quality of these areas from good to moderate grade over the 34-year period (r = -0.83, p < 0.05). Correlation analysis indicated that the remote sensing ecological index was positively correlated with lake area (r = 0.85, p < 0.01). The results indicate that steps should be taken to decrease the impact of human activities on the terrestrial ecological environmental quality of lake basins in semiarid zones.

Strengthened Surface Modification for High-Performance Inorganic Perovskite Solar Cells with 21.3% Efficiency.

Metal halide inorganic perovskites show excellent thermal stability compared to organic-inorganic perovskites. However, the performance of inorganic perovskite solar cells (PSCs) is far from theoretical values, together with unsatisfactory stability, mainly due to the poor interfacial properties. In this work, a facial but effective method is reported to realize high-performance inorganic PSCs by post-modifying the perovskite surface with 2-thiophene ethylamine (TEA). It is found that amine group from TEA can favorably interact with the undercoordinated Pb2+ via Lewis acid-based coordination, while thiophene ring with electron-rich sulfur assists such interaction by functioning as an electron donor. The synergetic interaction allows TEA to passivate perovskite film defects more efficiently, as compared to phenethylamine (PEA) with less electron-donating ability. Moreover, perovskite valence band is slightly upward shift to match with hole transport material and facilitate hole transfer. These combinations result in a reduced non-radiative charge recombination and improved charge carrier lifetime. Consequently, PSCs with TEA modification shows a drastic improvement of VOC by 54 mV, yielding a champion PCE of 21.3%, much higher than the control PSCs (19.3%), along with improved ambient stability. This work demonstrates that surface modifier with an electron-rich moiety is critical for achieving efficient and stable inorganic PSCs.

Tailored Cysteine-Derived Molecular Structures toward Efficient and Stable Inorganic Perovskite Solar Cells.

Surface-defect-triggered non-radiative charge recombination and poor stability have become the main roadblock to continued improvement in inorganic perovskite solar cells (PSCs). Herein, the main culprits are identified on the inorganic perovskite surface by first-principles calculations, and to purposefully design a brand-new passivator, Boc-S-4-methoxy-benzyl-l-cysteine (BMBC), whose multiple Lewis-based functional groups (NH, S and CO) to suppress halide vacancies and coordinate with undercoordinated Pb2+ through typical Lewis baseacid reactions. The tailored electron-donating methoxyl group (CH3 O-) can cause an increased electron density on the benzene ring, which strengthens the interaction with undercoordinated Pb2+ via electrostatic interactions. This BMBC passivation can reduce the surface trap density, enlarge grains, prolong the charge lifetime, and cause a more suitable energy-level alignment. In addition, the hydrophobic tert-butyl in butoxycarbonyl (Boc-) group ensures that BMBC is uniformly covered and prevents harmful aggregation through steric repulsion at the perovskite/hole-transporting layer (HTL) interface, thus providing a hydrophobic umbrella to resist moisture invasion. Consequently, the combination of the above increases the efficiency of CsPbI3-x Brx PSC from 18.6% to 21.8%, the highest efficiency for this type of inorganic metal halide PSCs so far, as far as it is known. Moreover, the device exhibits higher environmental and thermal stability.

Lead(II) 2-Ethylhexanoate for Simultaneous Modulated Crystallization and Surface Shielding to Boost Perovskite Solar Cell Efficiency and Stability.

The bulk and surface of a perovskite light-harvesting layer are two pivotal aspects affecting its carrier transport and long-term stability. In this work, lead(II) 2-ethylhexanoate (LDE) is introduced via an antisolvent process into perovskite films to change the reaction kinetics of the crystallization process, resulting in a high-quality perovskite film. Meanwhile, a carboxyl functional group with a long alkyl chain coordinates with the Pb cation, reducing the defect density related to unsaturated Pb atoms. Moreover, the long alkyl chains form a protecting layer at the surface of the perovskite film to prevent chemical attack by water and air, prolonging the lifetime of perovskite devices. Consequently, the assembled device demonstrates a power conversion efficiency (PCE) of 24.84%. Both of the thermal and operational stability are significantly improved due to reduced ion-migration channels.

Establishment and Application of a Predictive Growth Kinetic Model of Salmonella with the Appearance of Two Other Dominant Background Bacteria in Fresh Pork.

To better guide microbial risk management and control, growth kinetic models of Salmonella with the coexistence of two other dominant background bacteria in pork were constructed. Sterilized pork cutlets were inoculated with a cocktail of Salmonella Derby (S. Derby), Pseudomonas aeruginosa (P. aeruginosa), and Escherichia coli (E. coli), and incubated at various temperatures (4-37 °C). The predictive growth models were developed based on the observed growth data. By comparing R2 of primary models, Baranyi models were preferred to fit the growth curves of S. Derby and P. aeruginosa, while the Huang model was preferred for E. coli (all R2 ≥ 0.997). The secondary Ratkowsky square root model can well describe the relationship between temperature and µmax (all R2 ≥ 0.97) or Lag (all R2 ≥ 0.98). Growth models were validated by the actual test values, with Bf and Af close to 1, and MSE around 0.001. The time for S. Derby to reach a pathogenic dose (105 CFU/g) at each temperature in pork was predicted accordingly and found to be earlier than the time when the pork began to be judged nearly fresh according to the sensory indicators. Therefore, the predictive microbiology model can be applied to more accurately predict the shelf life of pork to secure its quality and safety.

Chelate Coordination Strengthens Surface Termination to Attain High-Efficiency Perovskite Solar Cells.

Solar cell efficiency and stability are two key metrics to determine whether a photovoltaic device is viable for commercial applications. The surface termination of the perovskite layer plays a pivotal role in not only the photoelectric conversion efficiency (PCE) but also the stability of assembled perovskite solar cells (PSCs). Herein, a strong chelate coordination bond is designed to terminate the surface of the perovskite absorber layer. On the one hand, the ligand anions bind with Pb cations via a bidentate chelating bond to restrict the ion migration, and the chelate surface termination changes the surface from hydrophilic to hydrophobic. Both are beneficial to improving the long-term stability. On the other hand, the formation of the chelating bonding effectively eliminates the deep-level defects including PbI and Pb clusters on the Pb-I and FA-I terminations, respectively, as confirmed by theoretical simulation and experimental results. Consequently, the PCE is increased to 24.52%, open circuit voltage to 1.19 V, and fill factor to 81.53%; all three are among the highest for hybrid perovskite cells. The present strategy provides a straightforward means to enhance both the PCE and long-term stability of PSCs.

Polar Species for Effective Dielectric Regulation to Achieve High-Performance CsPbI3 Solar Cells.

Nonradiative losses caused by defects are the main obstacles to further advancing the efficiency and stability of perovskite solar cells (PSCs). There is focused research to boost the device performance by reducing the number of defects and deactivating defects; however, little attention is paid to the defect-capture capacity. Here, upon systematically examining the defect-capture capacity, highly polarized fluorinated species are designed to modulate the dielectric properties of the perovskite material to minimize its defect-capture radius. On the one hand, fluorinated polar species strengthen the defect dielectric-screening effect via enhancing the dielectric constant of the perovskite film, thus reducing the defect-capture radius. On the other, the fluorinated iodized salt replenishes the I-vacancy defects at the surface, hence lowering the defect density. Consequently, the power-conversion efficiency of an all-inorganic CsPbI3 PSC is increased to as high as 20.5% with an open-circuit voltage of 1.2 V and a fill factor of 82.87%, all of which are among the highest in their respective categories. Furthermore, the fluorinated species modification also produces a hydrophobic umbrella yielding significantly improved humidity tolerance, and hence long-term stability. The present strategy provides a general approach to effectually regulate the defect-capture radius, thus enhancing the optoelectronic performance.

Analysis of Key Control Points of Microbial Contamination Risk in Pork Production Processes Using a Quantitative Exposure Assessment Model.

Pork is one of the most common foods causing microbial foodborne diseases. Since pork directly enters the market after slaughtering, the control of microbial contamination in the slaughtering processes is the key to ensuring the quality and safety of pork. The contamination level of Escherichia coli, a health-indicator bacterium, can reflect the risk level of potential pathogens. In order to assess the E. coli exposure risk of pork during slaughtering and to identify the key control points, we established an E. coli quantitative exposure assessment model for swine-slaughtering processes in slaughterhouses of different sizes. The model simulation data indicated the E. coli contamination pattern on the surfaces of swine carcasses during slaughtering. The changes in E. coli contamination were analyzed according to the simulation data of each slaughtering process. It was found that the number of E. coli after trimming in big and small slaughterhouses increased to the maximum values for the whole processes, which were 3.63 and 3.52 log10 CFU/100 cm2, respectively. The risk contribution of each slaughtering process to the E. coli contamination on the surface of terminal swine carcasses can be determined by correlation analysis. Because the absolute value of correlation coefficient during the trimming process was maximum (0.49), it was regarded as the most important key control point. This result can be further proved via the multilocus sequence typing of E. coli. The dominant sequence type before trimming processes was ST10. ST1434 began to appear in the trimming process and then became the dominant sequence type in the trimming and pre-cooling processes. The model can provide a theoretical basis for microbial hygiene supervision and risk control in swine-slaughtering processes.

Strong spring winds accelerated the recruitment and reinvasion of cyanobacteria.

The reinvasion and recruitment of overwintering cyanobacteria in sediments in spring have an important impact on cyanobacterial blooms in summer and autumn, but until now, this process has not been observed in natural water bodies. In this study, wireless sensors and automatic water sample collection systems were used to carry out continuous high-frequency monitoring of cyanobacteria and related environmental indicators in Meiliang Bay, Lake Taihu, during a northwest wind event in spring. The results showed that there were many dormant cyanobacteria seeds in the sediments of Lake Taihu. These cyanobacterial seeds were easily resuspended from sediments, allowing them to reinvade and remain in the overlying water. Simultaneously, the water temperature exceeded the recovery temperature after the northwest wind event and the available light was sufficient to allow the reinvading cyanobacteria to recruit. The circadian photosynthetic rhythm of these recruited cyanobacteria eventually led to a rapid increase in dissolved oxygen in the water body during the south wind phase to a supersaturated state, and periodic diurnal fluctuations of the water body dissolved oxygen saturation curve. This study provided direct evidence for fully understanding the annual cycle of cyanobacterial blooms.

In-situ observations of internal dissolved heavy metal release in relation to sediment suspension in lake Taihu, China.

Despite laboratory experiments that have been performed to study internal heavy metal release, our understanding of how heavy metals release in shallow eutrophic lakes remains limited for lacking in-situ evidence. This study used automatic environmental sensors and a water sampling system to conduct high-frequency in-situ observations (1-hr intervals) of water environmental variables and to collect water samples (3-hr intervals), with which to examine the release of internal heavy metals in Lake Taihu, China. Under conditions of disturbance by strong northerly winds, sediment resuspension in both the estuary area and the lake center caused particulate heavy metal resuspension. However, the patterns of concentrations of dissolved heavy metals in these two areas were complex. The concentrations of dissolved Se and Mo increased in both areas, indicating that release of internal dissolved Se and Mo is triggered by sediment resuspension. The concentrations of dissolved Ni, Zn, As, Mn, Cu, V, and Co tended to increase in the estuary area but decrease in the lake center. The different trends between these two areas were controlled by pH and cyanobacteria, which are related to eutrophication. During the strong northerly winds, the decrease in concentrations of dissolved heavy metals in the lake center was attributable primarily to absorption by the increased suspended solids, and to growth-related assimilation or surface adsorption by the increased cyanobacteria. The findings of this study suggest that, short-term changes of environmental conditions are very important in relation to reliable monitoring and risk assessment of heavy metals in shallow eutrophic lakes.

An Outer Membrane Protein Involved in the Uptake of Glucose Is Essential for Cytophaga hutchinsonii Cellulose Utilization.

Cytophaga hutchinsonii specializes in cellulose digestion by employing a collection of novel cell-associated proteins. Here, we identified a novel gene locus, CHU_1276, that is essential for C. hutchinsonii cellulose utilization. Disruption of CHU_1276 in C. hutchinsonii resulted in complete deficiency in cellulose degradation, as well as compromised assimilation of cellobiose or glucose at a low concentration. Further analysis showed that CHU_1276 was an outer membrane protein that could be induced by cellulose and low concentrations of glucose. Transcriptional profiling revealed that CHU_1276 exerted a profound effect on the genome-wide response to both glucose and Avicel and that the mutant lacking CHU_1276 displayed expression profiles very different from those of the wild-type strain under different culture conditions. Specifically, comparison of their transcriptional responses to cellulose led to the identification of a gene set potentially regulated by CHU_1276. These results suggest that CHU_1276 plays an essential role in cellulose utilization, probably by coordinating the extracellular hydrolysis of cellulose substrate with the intracellular uptake of the hydrolysis product in C. hutchinsonii.

A small periplasmic protein essential for Cytophaga hutchinsonii cellulose digestion.

Cytophaga hutchinsonii is a gliding cellulolytic bacterium that is ubiquitously distributed in soil. The mechanism by which C. hutchinsonii achieves cellulose digestion, however, is still largely unknown. In this study, we obtained a C. hutchinsonii mutant that was defective in utilizing filter paper or Avicel as the sole carbon source by transposon mutagenesis. The interrupted gene locus, CHU_2981, encodes a hypothetical protein with only 130 amino acids. Cell fractionation and western blot detection of CHU_2981 fused with a C-terminal green fluorescence protein (GFP) indicated that CHU_2981 is located in the periplasm. The CHU_2981-disrupted mutant cells exhibited a significant growth defect on Avicel but not on glucose and cellobiose. The absence of CHU_2981 also resulted in a significant defect in colony spreading and individual cell motility compared to wild-type cells. Further analysis demonstrated that the CHU_2981-disrupted mutant cells exhibited a different profile of cellulose-absorbed outer membrane proteins from that of wild-type cells, in which protein varieties and amounts were markedly decreased. Our results showed that CHU_2981, the periplasmic non-cellulolytic protein, plays an important role in both cellulose utilization and cell motility probably by being involved in the appropriate production of outer membrane proteins.

Outer membrane proteins related to SusC and SusD are not required for Cytophaga hutchinsonii cellulose utilization.

Cytophaga hutchinsonii, a member of the phylum Bacteroidetes, employs a novel collection of cell-associated proteins to digest crystalline cellulose. Other Bacteroidetes rely on cell surface proteins related to the starch utilization system (Sus) proteins SusC and SusD to bind oligosaccharides and import them across the outer membrane for further digestion. These bacteria typically produce dozens of SusC-like porins and SusD-like oligosaccharide-binding proteins to facilitate utilization of diverse polysaccharides. C. hutchinsonii specializes in cellulose digestion and its genome has only two susC-like genes and two susD-like genes. Single and multiple gene deletions were constructed to determine if the susC-like and susD-like genes have roles in cellulose utilization. A mutant lacking all susC-like and all susD-like genes digested cellulose and grew on cellulose as well as wild-type cells. Further, recombinantly expressed SusD-like proteins CHU_0547 and CHU_0554 failed to bind cellulose or ß-glucan hemicellulosic polysaccharides. The results suggest that the Bacteroidetes Sus paradigm for polysaccharide utilization may not apply to the cellulolytic bacterium C. hutchinsonii.

Identification and characterization of a novel locus in Cytophaga hutchinsonii involved in colony spreading and cellulose digestion.

Cytophaga hutchinsonii, an aerobic cellulolytic soil bacterium, is capable of degrading crystalline cellulose and gliding over surface rapidly. The involved mechanisms, however, are largely unknown. Here, we used the mariner-based transposon HimarEm1 to screen for C. hutchinsonii mutants deficient in utilizing filter paper as the sole carbon source. A novel gene locus, chu_1719, encoding a hypothetical protein was identified, whose inactivation resulted in a compromised growth of C. hutchinsonii on filter paper. Further analysis revealed that disruption of chu_1719 suppressed colony spreading but had no significant effect on Avicel degradation in liquid medium. Carboxymethylcellulase (CMCase) activity of the mutant membrane proteins was reduced by about 40% as compared with the wild-type strain. Moreover, profiles of cellulose-adsorbed outer membrane proteins were significantly different between the mutant and wild-type (WT) strains. These results suggest that chu_1719 plays an important role in controlling the spreading motility and cellulose utilization probably by affecting the appropriate production of membrane proteins in C. hutchinsonii.