High-efficiency perovskite solar cells (PSCs) have experienced rapid development and attracted significant attention in recent years. The PSCs based on doctor bladed or slot-die coated perovskite films usually have lower power conversion efficiency (PCE) than that based on spin-coated perovskite films. In this work, we have developed an effective method, called glass rod-sliding and low pressure assisted solution processing composition engineering (GRS-LPASP), to manufacture high quality perovskite film in air. GRS-LPASP composition engineering effectively increases the grain size and thickness of perovskite films and reduces the defect density by increasing the contact area between the perovskite layer and the hole transport layer, thus leading an increased current density (Jsc) of perovskite solar cells. The device with GRS-LPASP composition engineering achieves a maximum PCE of 19.78%. The experimental results demonstrates that GRS-LPASP composition engineering is a feasible method to prepare high-efficiency PSCs. Moreover, GRS-LPASP composition engineering also provides a potential approach for the commercial production of PSCs.
The explosion of time series data in recent years has brought a flourish of new time series analysis methods, for forecasting, clustering, classification and other tasks. The evaluation of these new methods requires either collecting or simulating a diverse set of time series benchmarking data to enable reliable comparisons against alternative approaches. We propose GeneRAting TIme Series with diverse and controllable characteristics, named GRATIS, with the use of mixture autoregressive (MAR) models. We simulate sets of time series using MAR models and investigate the diversity and coverage of the generated time series in a time series feature space. By tuning the parameters of the MAR models, GRATIS is also able to efficiently generate new time series with controllable features. In general, as a costless surrogate to the traditional data collection approach, GRATIS can be used as an evaluation tool for tasks such as time series forecasting and classification. We illustrate the usefulness of our time series generation process through a time series forecasting application.
Zeng L, Zou L, Özsu TM, Hu L, Zhang F. GSI: GPU-friendly Subgraph Isomorphism, in 36th IEEE International Conference on Data Engineering, ICDE 2020, Dallas, TX, USA, April 20-24, 2020. IEEE; 2020:1249–1260.
It is of great significance to evaluate the heavy metal pollution of soil in the water source protection area. Taking Miyun Reservoir water source protection area as the research object,223 soil surface samples were collected from Miyun Reservoir water source protection area,and the contents of 8 heavy metals (Pb,Ni,Cu,Cr,Zn,Cd,Hg and As) were determined. The results showed that the average content of Hg and As in the overall study area were lower than the background value of Beijing soil,and the average content of the other 6 heavy metals were higher than the background value of Beijing soil. Soil heavy metal pollution degree and potential ecological risk were evaluated by the geo-accumulation index and potential ecological risk index,and the possible sources of heavy metals were analyzed. The standard rate of soil heavy metals in the study area was about 83%,and the risk of agricultural soil pollution was low. Cr and Cd in the study area were in the state of no-medium pollution,and the other 6 heavy metal elements were in the state of no pollution. The ecological hazard of Cd was moderate,and the other 7 heavy metal elements were slight,and the overall ecological hazards of the study area was moderate. Based on the analysis of heavy metal pollution and ecological risk in Miyun Reservoir water source protection area,reference for the prevention and control of heavy metal in soil and the protection of water source area in Beijing water source protection area were provided.评价水源保护区土壤重金属污染状况具有重要意义。以密云水库水源保护区为研究对象,采集223个表层土壤样品,测定了Pb、Ni、Cu、Cr、Zn、Cd 、Hg和As 8种重金属的含量。结果表明,整个研究区Hg、As的平均含量低于北京市土壤背景值,其余6种重金属平均含量均高于北京市土壤背景值。采用地累积指数法和 潜在生态风险指数法评估土壤重金属污染程度和潜在生态风险,并分析了重金属的可能来源。研究区内土壤重金属达标率约83%,农用地土壤污染风险低。研究区 Cr和Cd处于无-中污染状态,其余6种重金属元素处于无污染状态;Cd生态危害中等,其余7种重金属生态危害轻微,研究区整体生态危害中等。分析密云水 库水源保护区土壤重金属污染及其生态风险,能为北京市水源保护区土壤重金属污染防治与水源地保护提供参考依据。
Heterogeneous reactivity of N2O5 on aerosols is a critical parameter in assessing NOx fate, nitrate production, and particulate chloride activation. Accurate measurement of its uptake coefficient (gamma N2O5) and representation in air quality models are challenging, especially in the polluted environment. With an in situ aerosol flow-tube system, the gamma N2O5 was directly measured on ambient aerosols at two rural sites in northern and southern China. The results were analyzed together with the gamma N2O5 derived from previous field studies in China to obtain a holistic picture of gamma N2O5 uptake and the influencing factors under various climatic and chemical conditions. The field-derived or measured gamma N2O5 was generally promoted by the aerosol water content and suppressed by particle nitrate. Significant discrepancies were found between the measured gamma N2O5 and that estimated from laboratory-determined parameterizations. An observation-based empirical parameterization was derived in the present work, which better reproduced the mean value and variability of the observed gamma N2O5. Incorporating this new parameterization into a regional air quality model (WRF-CMAQ) has improved the simulation of N2O5, nitrogen oxides, and secondary nitrate in the polluted regions of China.
Reducing the voltage loss (Vloss) is a critical factor in optimizing the open-circuit voltage (Voc) and overall power-conversion efficiency (PCE) of polymer solar cells. In the current work, by designing a novel electron-accepting unit of coronenediimide (CDI) and using it as the main functional building block, a new polymer acceptor CDI-V is developed and applied to fabricate all-polymer solar cells. Compared with the perylenediimide-based polymer acceptors we previously reported, the current CDI-V polymer possesses a noticeably elevated lowest unoccupied molecular orbital (LUMO). Thereby, by virtue of the enlarged energy gap between the donor HOMO and acceptor LUMO, a high Voc value of 1.05 V is achieved by the all-polymer photovolatic device, along with an impressively low Vloss of 0.55 V. As remarkably, in spite of an extremely small LUMO level offset of 0.01 eV exhibited by the donor and acceptor polymers, effective charge separation still takes place in the all-polymer device, as evidenced by a proper short-circuit current (Jsc) of 9.5 mA·cm2 and a decent PCE of 4.63%.
Two-dimensional (2D) semiconductors hold great promise in flexible electronics because of their intrinsic flexibility and high electrical performance. However, the lack of facile synthetic and subsequent device fabrication approaches of high-mobility 2D semiconducting thin films still hinders their practical applications. Here, we developed a facile, rapid, and scalable solution-assisted method for the synthesis of a high-mobility semiconducting oxyselenide (Bi2O2Se) thin film by the selenization and decomposition of a precursor solution of Bi(NO3)3·5H2O. Simply by changing the rotation speed in spin-coating of the precursor solution, the thicknesses of Bi2O2Se thin films can be precisely controlled down to few atomic layers. The as-synthesized Bi2O2Se thin film exhibited a high Hall mobility of ∼74 cm2 V–1 s–1 at room temperature, which is much superior to other 2D thin-film semiconductors such as transition metal dichalcogenides. Remarkably, flexible top-gated Bi2O2Se transistors showed excellent electrical stability under repeated electrical measurements on flat and bent substrates. Furthermore, Bi2O2Se transistor devices on muscovite substrates can be readily transferred onto flexible polyvinyl chloride (PVC) substrates with the help of thermal release tape. The integration of a high-mobility thin-film semiconductor, excellent stability, and easy transfer onto flexible substrates make Bi2O2Se a competitive candidate for future flexible electronics.
Abstract On-chip electron sources with the advantages of high emission current and density, high emission efficiency, low working voltage, and easy fabrication are highly desired for scaling down free electron-based devices and systems, especially for realizing those on a chip, but remain challenging. Here, such an on-chip electron source is reported simply based on electroformed silicon oxide between concentric graphene films on silicon oxide substrate. It is demonstrated that electron emission from an electron emitter can be driven by a low voltage about 11 V, and a high emission efficiency of 33.6%. An on-chip electron source with 36 × 36 emitter array in an area of 594 × 594 µm2 exhibits an emission current up to 1 mA at 38 V working voltage, corresponding to a high emission density of 283 mA cm−2. Electron emission from the sources is thought to be generated from horizontal tunneling diodes formed in electroformed silicon oxide. Combined advantages of high emission current and density, high emission efficiency, low working voltage, and easy fabrication make this on-chip electron sources promising in realizing miniature and on-chip free electron-based devices and systems.
Abstract An important advancement towards the realization of miniaturized and fully integrated vacuum electronic devices will be the development of on-chip integrated electron sources with stable and reproducible performances. Here, the fabrication of high-performance on-chip thermionic electron micro-emitter arrays is demonstrated by exploiting suspended super-aligned carbon nanotube films as thermionic filaments. For single micro-emitter, an electron emission current up to ≈20 µA and density as high as ≈1.33 A cm−2 are obtained at a low-driven voltage of 3.9 V. The turn-on/off time of a single micro-emitter is measured to be less than 1 µs. Particularly, stable (±1.2% emission current fluctuation for 30 min) and reproducible (±0.2% driven voltage variation over 27 cycles) electron emission have been experimentally observed under a low vacuum of ≈5 × 10−4 Pa. Even under a rough vacuum of ≈10−1 Pa, an impressive reproducibility (±2% driven voltage variation over 20 cycles) is obtained. Moreover, emission performances of micro-emitter arrays are found to exhibit good uniformity. The outstanding stability, reproducibility, and uniformity of the thermionic electron micro-emitter arrays imply their promising applications as on-chip integrated electron sources.