The research on the polymer-based solar cells (PSCs) has attracted an increasing amount of attention in recent years because PSCs pose potential advantages over mainstream inorganic-based solar ...cells, such as significantly reduced material/fabrication costs, flexible substrates, and light weight of finished solar cells. The research community has made great progress in the field of bulk heterojunction (BHJ) polymer solar cells since its inception in 1995. The power conversion efficiency (PCE), a key parameter to assess the performance of solar cells, has increased from 1% in the 1990s to over 8% just recently. These great advances are mainly fueled by the development of conjugated polymers used as the electron-donating materials in BHJ solar cells. In this Perspective, we first briefly review the progress on the design of conjugated polymers for polymer solar cells in the past 16 years. Since a conjugated polymer can be arbitrarily divided into three constituting componentsthe conjugated backbone, the side chains, and the substituentswe then focus on the rational design of conjugated polymers by separately discussing the influence of each component on the physical and photovoltaic (PV) properties of these polymers. Special attention is paid to the design of donor–acceptor type low-band-gap polymers because this approach is prevailing in the literature with its unique features. In doing so, we strive to extract useful rules for the rational design of conjugated polymers with predictable properties. We conclude by proposing future research opportunities to achieve even higher PCEs for PSCs.
Herbicides have been increasingly used worldwide and a large amount of herbicide residue eventually enters the ocean via groundwater or surface run-off every year. However, the global coastal ...pollution status of herbicides and their negative impact on marine life (especially phytoplankton) in natural environmental concentrations are poorly understood except for few special environments (e.g. the Great Barrier Reef, Australia). Our field investigation of the distribution of ten triazine herbicides in the Bohai Sea and the Yellow Sea of China revealed that the concentrations of triazine herbicides exceeded the “No Observed Effect Concentrations” for phytoplankton. Their total concentrations could be as high as 6.61 nmol L−1. Based on the concentration addition model, the toxicity of herbicide homologues is usually cumulative, and the combined toxicity of these ten triazine herbicides could cause 13.2% inhibition on the chlorophyll a fluorescence intensity of a representative diatom species Phaeodactylum tricornutum Pt-1, which corresponds roughly to the toxicity of atrazine in an equivalent concentration of 14.08 nmol L−1. Atrazine in this equivalent-effect concentration could greatly inhibit the growth of cells, the maximum quantum efficiency of photosystem II (Fv/Fm), and nutrient absorption of Phaeodactylum tricornutum Pt-1. Transcriptome analysis revealed that multiple metabolic pathways (Calvin cycle, tricarboxylic acid (TCA) cycle, glycolysis/gluconeogenesis, etc.) related with photosynthesis and carbon metabolism were greatly disturbed, which might ultimately influence the primary productivity of coastal waters. Moreover, with the values of its bioaccumulation factor ranging from 69.6 to 118.9, atrazine was found to be accumulated in algal cells, which indicates that herbicide pollution might eventually affect the marine food web and even threaten the seafood safety of human beings.
Abbreviations: CAGR, Compound annual growth rate (%); PS I/II, photosystem I/II; N, NO3-N, NO2-N, and NH4-N; P, PO4-P; Si, SiO4-Si. Data on global herbicide usage in this figure are from the databases of the Food and Agriculture Organization of the United Nations (http://www.fao.org/statistics/databases/en/) and the following references (Gu and Wang, 2016; Archbold and Nosarzewski, 2018; GlobeNewswire, 2017). Display omitted
•Total concentration of 10 triazine herbicides in coastal waters reached risk levels.•Triazine herbicides at environmental concentrations showed toxic effects on diatom.•Atrazine can be highly accumulated in algal cells.•The photosynthesis and carbon metabolism of diatom were significantly disturbed.•Coastal pollution of herbicide is a growing threat to primary productivity.
Ternary solar cells enjoy both an increased light absorption width, and an easy fabrication process associated with their simple structures. Significant progress has been made for such solar cells ...with demonstrated efficiencies over 7%; however, their fundamental working principles are still under investigation. This Perspective is intended to offer our insights on the three major governing mechanisms in these intriguing ternary solar cells: charge transfer, energy transfer, and parallel-linkage. Through careful analysis of exemplary cases, we summarize the advantages and limitations of these three major mechanisms and suggest future research directions. For example, incorporating additional singlet fission or upconversion materials into the energy transfer dominant ternary solar cells has the potential to break the theoretical efficiency limit in single junction organic solar cells. Clearly, a feedback loop between fundamental understanding and materials selection is in urgent need to accelerate the efficiency improvement of these ternary solar cells.
In the last century, following the development of Earth System Science, the metallogenic system has become an important topic in the study of mineral deposits ...
Conventional wisdom dictates that the band gap and energy levels of a conjugated polymer are primarily determined by the molecular structure of the conjugated backbone, while the solubilizing alkyl ...chains should have a negligible impact on these properties. Hence the side chains should have minimal impact on the short circuit current (J sc) and open circuit voltage (V oc) of corresponding polymer based bulk heterojunction (BHJ) solar cells. Contrary to the “conventional wisdom”, we demonstrate that the side chain of a low band gap polymer (PNDT-DTBT) significantly impacts the observed V oc and J sc of the corresponding BHJ solar cell with variations as much as 100%, depending upon the length and shape of these alkyl chains. The observed difference in V oc and J sc is quantitatively correlated with a pre-exponential dark current term, J so, which accounts for the intermolecular interactions in the polymer/PCBM blends.
Polymers to be used in bulk heterojunction (BHJ) solar cells should maintain a low highest occupied molecular orbital (HOMO) energy level as well as a narrow band gap in order to maximize the open ...circuit voltage (V oc) and the short circuit current (J sc). To concurrently lower the HOMO energy level and the band gap, we propose to modify the donor−acceptor low band gap polymer strategy by constructing alternating copolymers incorporating a “weak donor” and a “strong acceptor”. As a result, the “weak donor” should help maintain a low HOMO energy level while the “strong acceptor” should reduce the band gap via internal charge transfer (ICT). This concept was examined by constructing a library of polymers employing the naphtho2,1-b:3,4-b’dithiophene (NDT) unit as the weak donor, and benzothiadiazole (BT) as the strong acceptor. PNDT-BT, designed under the “weak donor−strong acceptor” strategy, demonstrated both a low HOMO energy level of −5.35 eV and a narrow band gap of 1.59 eV. As expected, a noticeably high V oc of 0.83 V was obtained from the BHJ device of PNDT-BT blended with PCBM. However, the J sc (∼3 mA/cm2) was significantly lower than the maximum expected current from such a low band gap material, which limited the observed efficiency to 1.27% (with a 70 nm thin film). Further improvements in the efficiency are expected from these materials if new strategies can be identified to (a) increase the molecular weight and (b) improve the hole mobility while still maintaining a low HOMO energy level and a narrow band gap.
The Jurassic Linglong granites, intrusive into the North China Craton (NCC) in eastern China, provide a critical record of the first major episode of lithospheric-scale extension and magmatism in NE ...China during Mesozoic time. Our U–Pb zircon dating reveals that the Linglong granites were emplaced during 161–158 Ma, shortly after the inception of a shallow subduction of the Palaeo-Pacific plate beneath East Asia during Middle Jurassic time. These granites have high alkali contents (K2O + Na2O = 8–9 wt%), low MgO and Mg no. values and variable Cr–Ni abundances. Their relatively high Ba and Sr concentrations, relatively low heavy rare Earth element (HREE) and strongly fractionated REE patterns characterize them as high Ba–Sr granites. The negative whole-rock εNd(t) values ranging from −22.4 to −10.9 and wide-ranging zircon εHf(t) values of −39.1 to −1.5 suggest that magmas of the Linglong granites were produced by partial melting of a garnet-amphibolite-bearing lower crust of the Jiaobei Terrane and by re-melting of the Triassic ultrahigh-pressure (UHP) metamorphic rocks and alkaline suites of the Sulu Terrane. The occurrence in the granitic rocks of inherited zircons of the Neoarchaean, Palaeoproterozoic, Neoproterozoic, Palaeozoic and Triassic ages suggests that magmas of the Linglong granites interacted with the ancient crust in these terranes during their ascent. Asthenospheric upwelling, induced by the steepening and rapid rollback of the Palaeo-Pacific slab during Late Jurassic time, provided the heat source for the inferred lower crustal melting. Trench migration and thermal weakening of the crust caused extensional deformation and thinning in the eastern part of the NCC.
High‐powered polymer: Fluorinated benzothiadiazole was incorporated into a polymer that was used in a high‐performance solar cell. The model polymer 2 has decreased HOMO and LUMO energy levels and a ...similar band gap when compared with its nonfluorinated analogue 1. A bulk heterojunction device derived from 1 demonstrated a high power conversion efficiency of 7.2 % (5.0 % for 1).
Predicting the magnitude of herbicide impacts on marine primary productivity remains challenging because the extent of worldwide herbicide pollution in coastal waters and the concentration-response ...relationships of phytoplankton communities to multiple herbicides are unclear. By analyzing the spatiotemporal distribution of herbicides at 661 bay and gulf stations worldwide from 1990 to 2022, we determined median, third quartile and maximum concentrations of 12 triazine herbicides of 0.18 nmol L
, 1.27 nmol L
and 29.50 nmol L
(95%Confidence Interval: CI 1.06, 1.47), respectively. Under current herbicide stress, phytoplankton primary productivity was inhibited by more than 5% at 25% of the sites and by more than 10% at 10% of the sites (95%CI 3.67, 4.34), due to the inhibition of highly abundant sensitive species, community structure/particle size succession (from Bacillariophyta to Dinophyceae and from nano-phytoplankton to micro-phytoplankton), and resulting growth rate reduction. Concurrently, due to food chain cascade effects, the dominant micro-zooplankton population shifted from larger copepod larvae to smaller unicellular ciliates, which might prolong the transmission process in marine food chain and reduce the primary productivity transmission efficiency. As herbicide application rates on farmlands worldwide are correlated with residues in their adjacent seas, a continued future increase in herbicide input may seriously affect the stability of coastal waters.
Recent research advances on conjugated polymers for photovoltaic devices have focused on creating low band gap materials, but a suitable band gap is only one of many performance criteria required for ...a successful conjugated polymer. This work focuses on the design of two medium band gap (∼2.0 eV) copolymers for use in photovoltaic cells which are designed to possess a high hole mobility and low highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels. The resulting fluorinated polymer PBnDT−FTAZ exhibits efficiencies above 7% when blended with 6,6-phenyl C61-butyric acid methyl ester in a typical bulk heterojunction, and efficiencies above 6% are still maintained at an active layer thicknesses of 1 μm. PBnDT−FTAZ outperforms poly(3-hexylthiophene), the current medium band gap polymer of choice, and thus is a viable candidate for use in highly efficient tandem cells. PBnDT−FTAZ also highlights other performance criteria which contribute to high photovoltaic efficiency, besides a low band gap.
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