Alkali Cation Doping for Improving the Structural Stability of 2D Perovskite in 3D/2D PSCs.

3D/2D hybrid perovskite systems have been intensively investigated to improve the stability of perovskite solar cells (PSCs), whereas undesired crystallization of 2D perovskite during the film formation process could undermine the structural stability of 2D perovskite materials, which causes serious hysteresis of PSCs after aging. This issue is, however, rarely studied. The stability study for 3D/2D hybrid systems to date is all under the one-direction scan, and the lack of detailed information on the hysteresis after aging compromises the credibility of the stability results. In this work, by correlating the hysteresis of the hybrid PSCs with the 2D crystal structure, we find that the prompt 2D perovskite formation process easily induces numerous crystal imperfections and structural defects. These defects are susceptible to humidity attack and decompose the 2D perovskite to insulating long-chain cations and 3D perovskite, which hinder charge transfer or generate charge accumulation. Therefore, a large hysteresis is exhibited after aging the 3D/2D hybrid PSCs in an ambient environment, even though the reverse-scan power conversion efficiency (PCE) is found to be well-preserved. To address this issue, alkali cations, K+ and Rb+, are introduced into the 2D perovskite to exquisitely modulate the crystal formation, which gives rise to a higher crystallinity of 2D perovskite and a better film morphology with fewer defects. We achieved PCE beyond 21% due to the preferable charge transfer process and reduced nonradiative recombination losses. The structural features also bring about impressive moisture stability, which results in the corresponding PSCs retaining 93% of its initial PCE and negligible hysteresis after aging in an ambient atmosphere for 1200 h.

2,5-hexanedione induces bone marrow mesenchymal stem cell apoptosis via inhibition of Akt/Bad signal pathway.

2,5-Hexanedione (HD) is an important bioactive metabolite of n-hexane and mediates the neurotoxicity of parent compound. Studies show that HD induces apoptotic death of neural progenitor cells. However, its underlying mechanism remains unknown. Mesenchymal stem cells (MSCs) are multipotential stem cells with the ability to differentiate into various cell types and have been used as cell model for studying the toxic effects of chemicals on stem cells. In this study, we exposed rat bone marrow MSCs to 0, 10, 20, and 40 mM HD in vitro. Apoptosis and disruption of mitochondrial transmembrane potential were estimated by immunochemistry staining. The expression of Akt, Bad, phosphorylated Akt (p-Akt), and Bad (p-Bad) as well as cytochrome c in mitochondria and cytosol were examined by Western blot. Moreover, caspase 3 activity, viability, and death of cells were measured by spectrophotometry. Our results showed that HD induced cell apoptosis and increased caspase 3 activity. HD down-regulated the expression levels of p-Akt, p-Bad and induced MMP depolarization, followed by cytochrome c release. Moreover, HD led to a concentration-dependent increase in the MSCs death, which was relative to MSCs apoptosis. However, these toxic effects of HD on the MSCs were significantly mitigated in the presence of IGF, which could activate PI3 K/Akt pathway. These results indicated that HD induced mitochondria-mediated apoptosis in the MSCs via inhibiting Akt/Bad signaling pathway and apoptotic death of MSCs via the signaling pathway. These results might provide some clues for studying further the mechanisms of HD-induced stem cell apoptosis and adverse effect on neurogenesis.

Synthesis of Ultrastable Ag Nanoplates/Polyethylenimine-Reduced Graphene Oxide and Its Application as a Versatile Electrochemical Sensor.

Investigations on Ag nanostructures/reduced graphene oxide composites have been frequently reported, yet the morphology control of those loaded Ag nanocrystals is still challenging. We herein develop a facile method to grow triangular Ag nanoplates (AgP) on polyethylenimine-modified reduced graphene oxide (AgP/PEI-rGO). The AgP/PEI-rGO hybrids show unexpected high stability against chloride ions (Cl(-) ) and hydrogen peroxide (H2 O2 ), which is possibly due to the strong interaction between surface Ag atoms with the amine groups of PEI. In the chronoamperometry measurements for detecting H2 O2 , N2 H4 , and NaNO2 , the AgP/PEI-rGO hybrid shows very wide linear ranges (usually 10(-6) -10(-2)  mol L(-1) for H2 O2 , N2 H4 , and NaNO2 ) and low detection limits (down to ≈1×10(-7)  mol L(-1) ), which demonstrate the promising electrochemical sensor applications of these metal/graphene hybrids with well-defined morphologies and facets. In addition, this strategy could be extended to the deposition of other noble metals on rGO with controlled morphologies.

Ultrathin (∼30 µm) flexible monolithic perovskite/silicon tandem solar cell.

The efficiency of rigid perovskite/silicon tandem solar cells has reached 33.9%. However, there has been no report on flexible perovskite/silicon tandem solar cells due to the challenge of overcoming the poor light absorption of ultrathin silicon bottom cells while maintaining their mechanical flexibility. Herein, we report the first demonstration of the perovskite/silicon tandem solar cell based on flexible ultrathin silicon. We show that reducing the wafer thicknesses and feature sizes of the light-trapping textures can significantly improve the flexibility of silicon without sacrificing light utilization. In addition, the capping of the perovskite top cells can further improve the device's mechanical durability by shifting the neutral plane toward the silicon surface that is prone to fracture. Finally, the resulting ultrathin (∼30 µm) flexible perovskite/silicon tandem solar cell achieves a certified stabilized efficiency of 22.8% with an extremely high power-to-weight ratio of 3.12 W g-1. Moreover, the flexible tandems exhibit remarkable bending durability, maintaining 98.2% of their initial performance after 3000 bending cycles at a radius of only 1 cm.

Visualizing Interfacial Energy Offset and Defects in Efficient 2D/3D Heterojunction Perovskite Solar Cells and Modules.

Currently, the full potential of perovskite solar cells (PSCs) is limited by chargecarrier recombination owing to imperfect passivation methods. Here, the recombination loss mechanisms owing to the interfacial energy offset and defects are quantified. The results show that a favorable energy offset can reduce minority carriers and suppress interfacial recombination losses more effectively than chemical passivation. To obtain high-efficiency PSCs, 2D perovskites are promising candidates, which offer powerful field effects and require only modest chemical passivation at the interface. The enhanced passivation and charge-carrier extraction offered by the 2D/3D heterojunction PSCs has boosted their power conversion efficiency to 25.32% (certified 25.04%) for small-size devices and to 21.48% for a large-area module (with a designated area of 29.0 cm2 ). Ion migration is also suppressed by the 2D/3D heterojunction, such that the unencapsulated small-size devices maintain 90% of their initial efficiency after 2000 h of continuous operation at the maximum power point.

Surface Reconstruction for Efficient and Stable Monolithic Perovskite/Silicon Tandem Solar Cells with Greatly Suppressed Residual Strain.

Despite the swift rise in power conversion efficiency (PCE) to more than 32%, the instability of perovskite/silicon tandem solar cells is still one of the key obstacles to practical application and is closely related to the residual strain of perovskite films. Herein, a simple surface reconstruction strategy is developed to achieve a global incorporation of butylammonium cations at both surface and bulk grain boundaries by post-treating perovskite films with a mixture of N,N-dimethylformamide and n-butylammonium iodide in isopropanol solvent, enabling strain-free perovskite films with simultaneously reduced defect density, suppressed ion migration, and improved energy level alignment. As a result, the corresponding single-junction perovskite solar cells yield a champion PCE of 21.8%, while maintaining 100% and 81% of their initial PCEs without encapsulation after storage for over 2500 h in N2 and 1800 h in air, respectively. Remarkably, a certified stabilized PCE of 29.0% for the monolithic perovskite/silicon tandems based on tunnel oxide passivated contacts is further demonstrated. The unencapsulated tandem device retains 86.6% of its initial performance after 306 h at maximum power point (MPP) tracking under continuous xenon-lamp illumination without filtering ultraviolet light (in air, 20-35 °C, 25-75%RH, most often ≈60%RH).

Long-chain anionic surfactants enabling stable perovskite/silicon tandems with greatly suppressed stress corrosion.

Despite the remarkable rise in the efficiency of perovskite-based solar cells, the stress-induced intrinsic instability of perovskite active layers is widely identified as a critical hurdle for upcoming commercialization. Herein, a long-alkyl-chain anionic surfactant additive is introduced to chemically ameliorate the perovskite crystallization kinetics via surface segregation and micellization, and physically construct a glue-like scaffold to eliminate the residual stresses. As a result, benefiting from the reduced defects, suppressed ion migration and improved energy level alignment, the corresponding unencapsulated perovskite single-junction and perovskite/silicon tandem devices exhibit impressive operational stability with 85.7% and 93.6% of their performance after 3000 h and 450 h at maximum power point tracking under continuous light illumination, providing one of the best stabilities to date under similar test conditions, respectively.

Additive Engineering of the CuSCN Hole Transport Layer for High-Performance Perovskite Semitransparent Solar Cells.

CuSCN has been widely considered a promising candidate for low-cost and high-stable hole transport material in perovskite semitransparent solar cells (STSCs). However, the low conductivity of the solution-processed CuSCN hole transport layer (HTL) hinders the hole extraction and transport in devices, which makes it hard to achieve devices with high performance. Herein, we report a facile additive engineering approach to optimize the p conductivity of CuSCN HTLs in perovskite STSCs. The n-butylammonium iodide additive facilitates the formation of Cu2+ and generates more Cu vacancies in the CuSCN HTL. This realizes a significant enhancement of the hole concentration and p conductivity of the film. Moreover, the additive improves the solubility of the CuSCN precursor solution and results in a uniform coverage on the perovskite active layer. Therefore, the perovskite STSC with a high power conversion efficiency (PCE) of 19.24% has been achieved, which is higher than that of the spiro-OMeTAD (18.83%) and CuSCN (17.45%) counterparts. In addition, the unencapsulated CuSCN-based device retains 87.5% of the initial PCE after 20 days in the ambient atmosphere.

Protective effects of Radix Codonopsis on ischemia-reperfusion injury in rats after kidney transplantation.

PURPOSE: Kidney ischemia-reperfusion injury (IRI) after kidney transplant remains a major problem, separate from immune rejection that can lead to kidney transplant failure and graft function loss. Free radicals, disturbance of microcirculation and the inflammatory cascade appear to be the main contributors. Radix Codonopsis, a traditional Chinese drug used in vascular diseases, is an antioxidant and free radical scavenger. This study investigates the protective effect and underlying mechanisms of Radix Codonopsis extract saponins on kidney transplantation. METHODS: Renal transplantation was performed after rat kidneys had been stored for 1 h at 4°C. Blood urea nitrogen (BUN), serum creatinine (Scr), superoxide dismutase (SOD) and malondialdehyde (MDA) were assayed; bcl-2 and bax mRNA expression was detected using RT-PCR; bcl-2 and bax protein expression was detected by immunohistochemistry (IHC). Terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) was used to detect apoptotic cells and determine the apoptosis index (AI). Analysis of variance (ANOVA) followed by Dunnett's test was used when more than two groups were compared. RESULTS: Saponin-treated animals showed increased SOD levels accompanied by decreased MDA, Scr and BUN levels (p < 0.05 vs. untreated controls); bcl-2 mRNA and protein levels were increased in transplanted kidney from treated animals, while bax mRNA and protein levels were decreased (p < 0.05 vs. untreated controls). AI was significantly decreased in transplanted kidneys from treated animals relative to untreated controls (p < 0.05 vs. untreated controls). CONCLUSION: This study clearly demonstrates the protective effects on IRI after kidney transplantation, which may be explained by decreased lipid peroxidation and inhibition of apoptosis.

Multiple Roles of Cobalt Pyrazol-Pyridine Complexes in High-Performing Perovskite Solar Cells.

Chemical doping is a ubiquitously applied strategy to improve the charge-transfer and conductivity characteristics of spiro-OMeTAD, a hole-transporting material (HTM) used widely in solution-processed perovskite solar cells (PSCs). Cobalt(III) complexes are commonly employed HTM dopants, whose major role is to oxidize spiro-OMeTAD to provide p-doping for improved conductivity. The present work discloses additional, previously unknown important functions of cobalt complexes in the HTM films that influence the photovoltaic performance. Specifically, it is demonstrated that commercial p-dopant FK269 (bis(2,6-di(1H-pyrazol-1-yl)pyridine) cobalt(III) tris(bis(trifluoromethylsulfonyl)imide)) reduces the interfacial recombination and alleviates the decomposition of the perovskite layer under the action of tert-butylpyridine and lithium bis(trifluoromethanesulfonyl)imide. These effects are demonstrated for 1 cm2 perovskite solar cells that achieve a stabilized power conversion efficiency of 19% under 1 sun irradiation.

Taurine attenuates acrylamide-induced axonal and myelinated damage through the Akt/GSK3ß-dependent pathway.

Acrylamide (ACR), formed during the Maillard reaction induced by high temperature in food processing, is one of the main causes of neurodegenerative diseases. Taurine, a free intracellular ß-amino acid, is characterized by many functions, including antioxidation, anti-inflammatory, and neuroprotective properties. This promotes its application in the treatment of neurodegenerative diseases. In this study, the neuroprotective effects of taurine against ACR-induced neurotoxicity and the potential underlying mechanisms were explored. Rats were intoxicated with ACR and injected with taurine in different groups for totally 2 weeks between January and July 2017. Electron microscopic analysis was used to observe the changes in tissues of the rats. Meanwhile, the levels of proteins including p-Akt, p-GSK3ß, SIM312, and MBP were detected by Western blot. Furthermore, the GSK3ß phosphorylation in taurine-treated dorsal root ganglion (DRG) with ACR was examined in the presence of the Akt inhibitor, MK-2206. The analysis of behavioral performances and electron micrographs indicated that taurine treatment significantly attenuated the toxic manifestations induced by ACR and stimulated the growth of axons and the medullary sheath, which was associated with the activation of the Akt/GSK3ß signaling pathway. Mechanistically, it was found that taurine activated GSK3ß, leading to significant recovery of the damage in ACR-induced sciatic nerves. Furthermore, MK-2206, an inhibitor of Akt, was applied in DRG cells, suggesting that taurine-induced GSK3ß phosphorylation was Akt dependent. Our findings demonstrated that taurine attenuated ACR-induced neuropathy in vivo, in an Akt/GSK3ß-dependent manner. This confirmed the treatment with taurine to be a novel strategy against ACR-induced neurotoxicity.

Room-temperature solution-processed and metal oxide-free nano-composite for the flexible transparent bottom electrode of perovskite solar cells.

The exploration of low-temperature and solution-processed charge transporting and collecting layers can promote the development of low-cost and large-scale perovskite solar cells (PVSCs) through an all solution process. Here, we propose a room-temperature solution-processed and metal oxide-free nano-composite composed of a silver nano-network and graphene oxide (GO) flawless film for the transparent bottom electrode of a PVSC. Our experimental results show that the amount of GO flakes play a critical role in forming the flawless anti-corrosive barrier in the silver nano-network through a self-assembly approach under ambient atmosphere, which can effectively prevent the penetration of liquid or gaseous halides and their corrosion against the silver nano-network underneath. Importantly, we simultaneously achieve good work function alignment and surface wetting properties for a practical bottom electrode by controlling the degree of reduction of GO flakes. Finally, flexible PVSC adopting the room-temperature and solution-processed nano-composite as the flexible transparent bottom electrode has been demonstrated on a polyethylene terephthalate (PET) substrate. As a consequence, the demonstration of our room-temperature solution-processed and metal oxide-free flexible transparent bottom electrode will contribute to the emerging large-area flexible PVSC technologies.

Modelling photosynthesis in flag leaves of winter wheat (Triticum aestivum) considering the variation in photosynthesis parameters during development.

The Farquhar-von Caemmerer-Berry (FvCB) model of photosynthesis has been widely used to estimate the photosynthetic C flux of plants under different growth conditions. However, the seasonal fluctuation of some photosynthesis parameters (e.g. the maximum carboxylation rate of Rubisco (Vcmax), the maximum electron transport rate (Jmax) and internal mesophyll conductance to CO2 transport (gm)) is not considered in the FvCB model. In this study, we investigated the patterns of the FvCB parameters during flag leaf development based on measured photosynthesis-intercellular CO2 curves in two cultivars of winter wheat (Triticum aestivum L.). Parameterised seasonal patterns of photosynthesis parameters in the FvCB model have subsequently been applied in order to predict the photosynthesis of flag leaves. The results indicate that the Gaussian curve characterises the dynamic patterns of Vcmax, Jmax and gm well. Compared with the model with fixed photosynthesis parameter values, updating the FvCB model by considering seasonal changes in Vcmax and Jmax during flag leaf development slightly improved predictions of photosynthesis. However, if the updated FvCB model incorporated the seasonal patterns of Vcmax and Jmax, and also of gm, predictions of photosynthesis was improved a lot, matching well with the measurements (R2=0.87, P<0.0001). This suggests that the dynamics of photosynthesis parameters, particularly gm, play an important role in estimating the photosynthesis rate of winter wheat.

Evidence of widespread ozone-induced visible injury on plants in Beijing, China.

Despite the high ozone levels measured in China, and in Beijing in particular, reports of ozone-induced visible injury in vegetation are very scarce. Visible injury was investigated on July and August 2013 in the main parks, forest and agricultural areas of Beijing. Ozone injury was widespread in the area, being observed in 28 different species. Symptoms were more frequent in rural areas and mountains from northern Beijing, downwind from the city, and less frequent in city gardens. Among crops, injury to different types of beans (genera Phaseolus, Canavalia and Vigna) was common, and it was also observed in watermelon, grape vine, and in gourds. Native species such as ailanthus, several pines and ash species were also symptomatic. The black locust, the rose of Sharon and the Japanese morning glory were among the injured ornamental plants. Target species for broader bio-monitoring surveys in temperate China have been identified.

Shape evolution of Au nanoring@Ag core-shell nanostructures: diversity from a sole seed.

Au nanoring@Ag core-shell nanostructures with controllable morphologies and tunable symmetries are synthesized via the seed-mediated growth of Ag onto a sole seed: a circular Au nanoring (AuNR). The 2D isotropic AuNR is prepared firstly by chemical etching, then by galvanic replacement with HAuCl4. By delicately altering the regrowth procedure and mixing the capping agents, different Ag triangular nanoplates with embedded AuNRs in different sizes and shapes can be obtained. Furthermore, by using a single capping agent, the growth of Ag on the AuNR can be preferentially confined to a lateral or vertical mode, to form eccentric nanoplates or nanocubes in both sequence sets at room temperature. Such nanostructures with precisely controllable shape evolution not only displayed unique optical properties, but also revealed the feasibility of breaking the original dimensions, and especially symmetry, at the nanoscale using seed-mediated growth. This paves the way for future applications including catalysis, diagnosis, plasmonics, and biological and chemical sensing.

[Influence of ozone on snap bean under ambient air in two sites of northern China].

Tropospheric ozone (O3) has been assumed the most phytotoxic air pollutant and the snap bean (Phaseolus vulgaris L.) is known to be an ozone-sensitive species. Two genotypes (R123, ozone-tolerance, S156, ozone-sensitivity) of snap bean were explored in three places. The objective of this study was to evaluate whether the snap bean was influenced under the current ambient ozone concentration. The findings indicated that the leaves of bean grown at Research Center for Eco-Environmental Sciences (RCEES), Chinese Academy of Sciences and ChangPing showed visible ozone symptoms under the ambient ozone concentration, and the averaged ozone injury proportion in S156 was 23.5% higher than R123 during the entire growth season. The ozone damage to the snap bean depends on the plant growing stages. The injury symptoms appeared just after flowering, increased from the stages of flowering to pod formation, and reached the maximum at the stages of pod maturation. The ratio of S156/R123 in pod yield was 0.48, and 0.24 and 0.73 in the RCEES, ChangPing and Harbin, respectively. The ratio close to 1 was assumed that the plant growth is not affected by ozone, and the lower ratio is, the more damage caused by ozone. Obviously, the current ambient ozone concentration of Beijing area has significantly caused the yield loss of snap bean.

[Dynamic simulation of photosynthate allocation in maize organs based on functional equilibrium hypothesis].

By using the 2004-2008 observation data of maize biomass and related environmental factors from the Jinzhou Agricultural Ecosystem Research Station of Shenyang Institute of Atmospheric Environment under China Meteorological Administration (CMA), the Friedlingstein model was validated and tested at station site and daily time scales. A model of soil available nutrient coefficient for maize field was developed, based on fertilization, soil temperature, and soil available water; and a daily time scale maize photosynthate allocation model was built, according to the functional equilibrium hypothesis. Comparing with Friedlingstein model, the daily time scale maize photosynthate allocation model could give more accurate simulation of photosynthate allocation in maize root, stem, and leaf, and provide technical support for accurate simulation of daily net primary productivity of maize agro-ecosystem.