There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low ...efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSn
Ge
I
) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.11%. More importantly, these PSCs show very high stability, with less than 10% decay in efficiency after 500 h of continuous operation in N
atmosphere under one-sun illumination. The key to this striking performance of these PSCs is the formation of a full-coverage, stable native-oxide layer, which fully encapsulates and passivates the perovskite surfaces. The native-oxide passivation approach reported here represents an alternate avenue for boosting the efficiency and stability of lead-free PSCs.
With efficiencies exceeding 20% and low production costs, lead halide perovskite solar cells (PSCs) have become potential candidates for future commercial applications. However, there are serious ...concerns about their long-term stability and environmental friendliness, heavily related to their commercial viability. Herein, we present a theoretical investigation based on the ab initio molecular dynamics (AIMD) simulations and the first-principles density functional theory (DFT) calculations to investigate the effects of sunlight and moisture on the structures and properties of MAPbI3 perovskites. AIMD simulations have been performed to simulate the impact of a few water molecules on the structures of MAPbI3 surfaces terminated in three different ways. The evolution of geometric and electronic structures as well as the absorption spectra has been shown. It is found that the PbI2-terminated surface is the most stable while both the MAI-terminated and PbI2-defective surfaces undergo structural reconstruction, leading to the formation of hydrated compounds in a humid environment. The moisture-induced weakening of photoabsorption is closely related to the formation of hydrated species, and the hydrated crystals MAPbI3·H2O and MA4PbI6·2H2O scarcely absorb the visible light. The electronic excitation in the bare and water-absorbed MAPbI3 nanoparticles tends to weaken Pb-I bonds, especially those around water molecules, and the maximal decrease of photoexcitation-induced bond order can reach up to 20% in the excited state in which the water molecules are involved in the electronic excitation, indicating the accelerated decomposition of perovskites in the presence of sunlight and moisture. This work is valuable for understanding the mechanism of chemical or photochemical instability of MAPbI3 perovskites in the presence of moisture.
Human activities have shaped large-scale distributions of many species, driving both range contractions and expansions. Species differ naturally in range size, with small-range species concentrated ...in particular geographic areas and potentially deviating ecologically from widespread species. Hence, species’ responses to human activities may be influenced by their geographic range sizes, but if and how this happens are poorly understood. Here, we use a comprehensive distribution database and species distribution modeling to examine if and how human activities have affected the extent to which 9,701 vascular plants fill their climatic potential ranges in China. We find that narrow-ranged species have lower range filling and widespread species have higher range filling in the human-dominated southeastern part of China, compared with their counterparts distributed in the less human-influenced northwestern part. Variations in range filling across species and space are strongly associated with indicators of human activities (human population density, human footprint, and proportion of cropland) even after controlling for alternative drivers. Importantly, narrow-ranged and widespread species show negative and positive range-filling relationships to these human indicators, respectively. Our results illustrate that floras risk biotic homogenization as a consequence of anthropogenic activities, with narrow-ranged species becoming replaced by widespread species. Because narrow-ranged species are more numerous than widespread species in nature, negative impacts of human activities will be prevalent. Our findings highlight the importance of establishing more protected areas and zones of reduced human activities to safeguard the rich flora of China.
Temporal action proposal generation is an essential step for untrimmed video analysis and gains much attention from academia. However, most of the prior works predict the confidence score of each ...proposal separately and neglect the relations between proposals, limiting their performance. In this work, we design a novel Content Temporal Relation Network (CTRNet) to generate temporal action proposals by exploring the content and temporal semantic relations between proposals simultaneously. Specifically, we design a proposal feature map generation layer to convert the temporal semantic relations of proposals into spatial relations. Based on the proposal feature map, we propose a content-temporal relation module, which applies a novel adaptive-dilated convolution to model the temporal semantic relations between proposals and designs a content-adaptive convolution operation to explore the content semantic relation between proposals. Considering the temporal and content semantic relations between proposals, CTRNet has learned discriminative proposal features to improve performance. Extensive experiments are performed on two mainstream temporal action detection datasets, and CTRNet significantly outperforms the previous state-of-the-art methods. The codes are available at https://github.com/YanZhang-bit/CTRNet.
•Our method is the first framework to exploit the content and temporal semantic relations between proposals to generate temporal action proposals.•We propose a novel adaptive-dilate Conv, whose dilate rate is adaptive to the spatial position, to model the temporal semantic relations.•We adopt the attention mechanism to design a content-adaptive convolution operation to model the content semantic relations between proposals.•Our method outperforms the state-of-the-art methods on the THUMOS14 dataset.
The alloying behavior between FAPbI3 and CsSnI3 perovskites is studied carefully for the first time, which has led to the realization of single‐phase hybrid perovskites of (FAPbI3)1−x(CsSnI3)x ...(0<x<1) compositions with anomalous bandgaps. (FAPbI3)1−x(CsSnI3)x perovskites exhibit stable, homogenous composition/microstructure at the nanoscale, as confirmed by microscopic characterization. The ideal bandgap of 1.3 eV for single‐junction solar cell operation is achieved in the rationally‐tailored (FAPbI3)0.7(CsSnI3)0.3‐composition perovskite. Solar cells based on this new perovskite show power conversion efficiency up to 14.6 %.
Thin‐film photovoltaics: Significant progress has been made on the formation of mixed cation‐stablized Pb–Sn alloy perovskite materials made from FAPbI3 and CsSnI3 halide perovskites (FA=formamidinium). Solar cells based on an alloy in this system with an ideal bandgap show power conversion efficiencies up to 14.6 %.
Tin organic–inorganic halide perovskites (tin OIHPs) possess a desirable band gap and their power conversion efficiency (PCE) has reached 14 %. A commonly held view is that the organic cations in tin ...OIHPs would have little impact on the optoelectronic properties. Herein, we show that the defective organic cations with randomly dynamic characteristics can have marked effect on optoelectronic properties of the tin OIHPs. Hydrogen vacancies originated from the proton dissociation from FA HC(NH2)2 in FASnI3 can induce deep transition levels in the band gap but yield relatively small nonradiative recombination coefficients of 10−15 cm3 s−1, whereas those from MA (CH3NH3) in MASnI3 can yield much larger nonradiative recombination coefficients of 10−11 cm3 s−1. Additional insight into the “defect tolerance” is gained by disentangling the correlations between dynamic rotation of organic cations and charge‐carrier dynamics.
To achieve higher power conversion efficiency for tin organic–inorganic halide perovskites the critical role of organic defects in nonradiative recombination should be better understood. Random rotation of organic cation can suppress nonradiative carrier trapping owing to organic defects in FASnI3 FA=HC(NH2)2, rendering the organic contributions for defect tolerance. In contrast, organic defects in MASnI3 (MA=CH3NH3) are strong and active trapping centers.
2D hybrid halide double perovskites (HHDPs) have been demonstrated to be a promising alternative to conventional lead‐based halide perovskites as a new system of photoferroelectrics, due to their ...unique characteristics of environmental friendliness, favorable stability, and fascinating optoelectronic properties. Herein, for the first time, a 2D iodide double perovskite photoferroelectric is reported based on Ag/Sb ions, (4,4‐DFPD)4AgSbI8 (4,4‐DFPD = 4,4‐difluoropiperidinium), which possesses a high Curie temperature of 414 K (above BaTiO3), a large spontaneous polarization of 9.6 μC cm−2, ferroelectric photovoltaic effect, and photostrictive effect. Notably, to the best of the authors’ knowledge, the discovery of photostriction in HHDP photoferroelectrics is unprecedented. Moreover, (4,4‐DFPD)4AgSbI8 exhibits an impressive X‐ray responsivity, with a sensitivity as high as 704.8 μC Gyair−1 cm−2 at 100 V bias and a detection limit as low as 0.36 μGyair s−1 at 10 V bias, both of which outperform the current all HHDP photoferroelectrics. This work enriches the photoferroelectric family, and proves that Ag/Sb‐based HHDP photoferroelectrics are a promising candidate for the next‐generation optoelectronic devices.
The first silver/antimony‐based double perovskite photoferroelectric, (4,4‐difluoropiperidinium)4AgSbI8, is discovered, which exhibits ferroelectric photovoltaic effect and photostrictive effect under light radiation. Moreover, (4,4‐difluoropiperidinium)4AgSbI8 exhibits an exciting X‐ray responsivity including a sensitivity as high as 704.8 μC Gyair−1 cm−2 at 100 V bias and a detection limit as low as 0.36 μGyair s–1, both of which are the best among all HHDP photoferroelectrics.
Temporal action detection is a challenging task in video understanding, which is usually divided into two stages: proposal generation and classification. Learning proposal features is a crucial step ...for both stages. However, most methods ignore temporal information of proposals and consider background and action frames in proposals equally, leading to poor proposal features. In this paper, we propose a novel Temporal Attention-Pyramid Pooling (TAPP) method to learn proposal features of arbitrary length action proposals. The TAPP method exploits the attention mechanism to focus on the discriminative part of proposals, suppressing background influence on proposal features. It constructs a temporal pyramid structure to convert arbitrary length proposal feature sequences to multiple fixed-length sequences while retaining the temporal information. In the TAPP method, we design a multi-scale temporal function and apply it to the temporal pyramid to generate final proposal features. Based on the TAPP method, we construct a temporal action proposal generation model and an action proposal classification model, and then we perform extensive experiments on two mainstream temporal action detection datasets for the temporal action proposal and temporal action detection tasks to verify our models. On the THUMOS'14 dataset, our models based on the TAPP significantly outperform the previous state-of-the-art methods for both tasks.
Formamidinium (FA)‐based lead iodide perovskites have emerged as the most promising light‐absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the ...phase‐instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA‐based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA‐based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but also enhances the charge‐carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment‐theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000‐h storage under ambient conditions.
Formamidinium‐based perovskite thin films containing in situ silica‐encapsulated grains are prepared by integrating the tetraethylorthosilicate hydrolysis in the perovskite crystallization process. This novel strategy protects perovskite films from degradation and enhances their physical properties, leading to highly efficient and stable perovskite solar cells.
The abundance and composition of soil ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were investigated by using quantitative real-time polymerase chain reaction, cloning and ...sequencing approaches based on amoA genes. The soil, classified as agri-udic ferrosols with pH (H₂O) ranging from 3.7 to 6.0, was sampled in summer and winter from long-term field experimental plots which had received 16 years continuous fertilization treatments, including fallow (CK0), control without fertilizers (CK) and those with combinations of fertilizer nitrogen (N), phosphorus (P) and potassium (K): N, NP, NK, PK, NPK and NPK plus organic manure (OM). Population sizes of AOB and AOA changed greatly in response to the different fertilization treatments. The NPK + OM treatment had the highest copy numbers of AOB and AOA amoA genes among the treatments that received mineral fertilizers, whereas the lowest copy numbers were recorded in the N treatment. Ammonia-oxidizing archaea were more abundant than AOB in all the corresponding treatments, with AOA to AOB ratios ranging from 1.02 to 12.36. Significant positive correlations were observed among the population sizes of AOB and AOA, soil pH and potential nitrification rates, indicating that both AOB and AOA played an important role in ammonia oxidation in the soil. Phylogenetic analyses of the amoA gene fragments showed that all AOB sequences from different treatments were affiliated with Nitrosospira or Nitrosospira-like species and grouped into cluster 3, and little difference in AOB community composition was recorded among different treatments. All AOA sequences fell within cluster S (soil origin) and cluster M (marine and sediment origin). Cluster M dominated exclusively in the N, NP, NK and PK treatments, indicating a pronounced difference in the community composition of AOA in response to the long-term fertilization treatments. These findings could be fundamental to improve our understanding of the importance of both AOB and AOA in the cycling of nitrogen and other nutrients in terrestrial ecosystems.
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