The West Antarctic Ice Sheet (WAIS) is considered the major contributor to global sea level rise in the Last Interglacial (LIG) and potentially in the future. Exposed fossil reef terraces suggest sea ...levels in excess of 7 m in the last warm era, of which probably not much more than 2 m are considered to originate from melting of the Greenland Ice Sheet. We simulate the evolution of the Antarctic Ice Sheet during the LIG with a 3‐D thermomechanical ice sheet model forced by an atmosphere‐ocean general circulation model (AOGCM). Our results show that high LIG sea levels cannot be reproduced with the atmosphere‐ocean forcing delivered by current AOGCMs. However, when taking reconstructed Southern Ocean temperature anomalies of several degrees, sensitivity studies indicate a Southern Ocean temperature anomaly threshold for total WAIS collapse of 2–3°C, accounting for a sea level rise of 3–4 m during the LIG. Potential future Antarctic Ice Sheet dynamics range from a moderate retreat to a complete collapse, depending on rate and amplitude of warming.
Key Points
Southern Ocean temperature thresholds of 2–3°C for LIG WAIS collapse
Twin peak Antarctic Last Interglacial sea level contribution
Potential future WAIS dynamics range from moderate retreat to complete collapse
Perovskite/silicon tandem solar cells are regarded as a promising candidate to surpass current efficiency limits in terrestrial photovoltaics. Tandem solar cell efficiencies meanwhile reach more than ...29%. However, present high-end perovskite/silicon tandem solar cells still suffer from optical losses. We review recent numerical and experimental perovskite/silicon tandem solar cell studies and analyse the applied measures for light management. Literature indicates that highest experimental efficiencies are obtained using fully planar perovskite top cells, being in contradiction to the outcome of optical simulations calling for textured interfaces. The reason is that the preferred perovskite top cell solution-processing is often incompatible with usual micropyramidal textures of silicon bottom cells. Based on the literature survey, we propose a certain gentle nanotexture as an example to reduce optical losses in perovskite/silicon tandem solar cells. Optical simulations using the finite-element method reveal that an intermediate texture between top and bottom cell does not yield an optical benefit when compared with optimized planar designs. A double-side textured top-cell design is found to be necessary to reduce reflectance losses by the current density equivalent of 1 mA/cm
. The presented results illustrate a way to push perovskite/silicon tandem solar cell efficiencies beyond 30% by improved light management.
Light management strategies can increase the efficiency of perovskite single-junction and tandem solar cells. In this study, we present perovskite solar cells deposited on different shallow ...nanotextures by spin-coating. A morphological and optoelectronic analysis demonstrates a high quality of the perovskite absorber, regardless of the substrate. Using both, a nanotexture and a sodium fluoride antireflective coating, enables us to improve the power conversion efficiency by 1.0%abs to 19.7%, when compared to its planar reference. A characterization of the optical performance of nanotextured perovskite solar cells and rigorous optical simulations reveal that the gain in efficiency can be largely attributed to reduced reflection losses and therefore increased absorption in the perovskite. Our nanotextured perovskite solar cells reach 93.6% of the attainable current density, marking the highest reported value for perovskite single-junctions and approaching those of established photovoltaic technologies. Our results demonstrate that nanotextures can be applied to solution-processed perovskite solar cells and pave the way to increased power conversion efficiencies by light management not only in perovskite single-junction but also perovskite–silicon tandem solar cells.
•Mixtures of 1-methylimidazolium acetate and 1-methylimidazolium trifluoroacetate allow tuning electrolyte properties.•Dielectric relaxation spectroscopy and NMR chemical shifts show that ...trifluoroacetate results in enhanced protonation, less dynamic correlations, and enhanced conductance.•Diffusion ordered NMR indicates that addition of trifluoroactate can enhance Grotthuss-type charge transport.•Protic and aprotic solvents can enhance and suppress conductivity, respectively.
Despite the potential to overcome slow charge transport in ionic liquids by decoupling charge transport from mass transport in protic ionic liquids (PILs), the average proton distribution and the contribution of proton conduction to the overall charge transport in PILs has not been fully established. To elucidate the predominant underlying molecular species in the PILs and the molecular dynamics of the PILs, we study the dipolar response and conductivity using dielectric relaxation (DR) spectroscopy and the nucleis chemical environment and molecular mobility using nuclear magnetic resonance (NMR) spectroscopy of prototypical PILs based on 1–methylimidazolium as Brønsted base. To elucidate the effect of the acidity of the Brønsted acid we gradually vary the composition of the PILs from 1–methylimidazoliumacetate MimHAcO to 1–methylimidazoliumtrifluoroacetate MimHTFA. Both, 15N-NMR chemical shifts and the sample conductivities suggest that in neat MimHAcO electro-neutral molecular species dominate, consistent with earlier findings. The dipolar response of these molecular species as detected via the DR spectra is stronger than what one would expect based on the molecular dipole moments estimated from density functional theory calculations, which points to the formation of an extended hydrogen-bonded network. Upon addition of MimHTFA, this dipolar response is reduced as the degree of protonation of 1–methylimidazolium gradually increases, which is apparent from the conductance and 15N chemical shifts. Interestingly, diffusion ordered NMR spectroscopy indicates protons to become more mobile than the constituting acid and base molecules, consistent with Grotthuss-like proton transport. To vary the immediate environment of the PILs, we study solutions of the PIL mixtures in aprotic dimethylformamide (DMF) and protic methanol (MeOH) as two limiting cases. We find that MimHAcO exclusively forms electroneutral species in DMF, as evident from the negligible conductivity, while with increasing TFA content the fraction of charged molecular species increases. Although these ionic species give rise to a finite conductivity, demonstrating the presence of mobile ions, a large fraction of these ions is bound in MimHTFA ion-pairs, as detected in the DR spectra. Yet, temperature dependent 1H-NMR linewidths of the acidic proton signals suggest proton exchange to occur on the NMR timescale, presumably between MimH+ and Mim. Conversely, in MeOH we find no evidence for the presence of ion-pairs, while the high conductivity of these solutions shows that MeOH can efficiently solvate ions and may participate in proton transfer. Together, our results highlight the sensitivity of protonation equilibria to the immediate environment and of proton dynamics to these protonation equilibria. Our results show that tuning these equilibria using PIL mixtures can provide routes to tailor the contribution of proton transport to charge transport in PILs.
Abstract
Perovskite–silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been ...presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.
Using a combination of experimental measurements and polarizable molecular dynamics simulations, we investigate the dielectric spectra of the protic ionic liquid 1-methylimidazolium acetate, shedding ...light on their dynamic behavior and intermolecular interactions when adding 1-methylimidazolium trifluoroacetate to increase the fraction of a strong Brønsted acid in the system. The comparison between experimental and computational results provides valuable insights into the accuracy of the simulation models (with and without explicit proton transfer) and the ability to capture the intricate dynamical features of the protic ionic liquid. The investigation revealed complete deprotonation of trifluoroacetate, inducing a shift in the ionic liquid towards a more pronounced ionic state. The computational decomposition of the dielectric spectra into molecular translational and rotational contributions unveiled a reduction in the dielectric constant. This reduction was primarily ascribed to a decrease in translational contributions. Additionally, a strong correlation of the mutual orientation of molecules was found. The observed rise in conductivity upon the addition of 1-methylimidazolium trifluoroacetate to the system was attributed to an increase in proton transport.
•Trifluoroacetate is completely deprotonated.•Reduction in the dielectric constant due to decrease of translational contributions.•Strong correlation of molecular orientation.•Increase in conductivity due to rise of proton transport.
Ice-sheet models are a powerful tool to project the evolution of the Greenland and Antarctic ice sheets and thus their future contribution to global sea-level changes. Testing the ability of ...ice-sheet models to reproduce the ongoing and past evolution of the ice cover in Greenland and Antarctica is a fundamental part of every modelling effort. However, benchmarking ice-sheet model results against real-world observations is a non-trivial process as observational data come with spatiotemporal gaps in coverage. Here, we present a new approach to assess the accuracy of ice-sheet models which makes use of the internal layering of the Antarctic ice sheet. We calculate isochrone elevations from simulated Antarctic geometries and velocities via passive Lagrangian tracers, highlighting that a good fit of the model to two-dimensional datasets such as surface velocity and ice thickness does not guarantee a good match against the 3D architecture of the ice sheet and thus correct evolution over time. We show that palaeoclimate forcing schemes derived from ice-core records and climate models commonly used to drive ice-sheet models work well to constrain the 3D structure of ice flow and age in the interior of the East Antarctic ice sheet and especially along ice divides but fail towards the ice-sheet margin. The comparison to isochronal horizons attempted here reveals that simple heuristics of basal drag can lead to an overestimation of the vertical interior ice-sheet flow especially over subglacial basins. Our model observation intercomparison approach opens a new avenue for the improvement and tuning of current ice-sheet models via a more rigid constraint on model parameterisations and climate forcing, which will benefit model-based estimates of future and past ice-sheet changes.
Photoactive complexes with earth-abundant metals have attracted increasing interest in the recent years fueled by the promise of sustainable photochemistry. However, sophisticated ligands with ...complicated syntheses are oftentimes required to enable photoactivity with nonprecious metals. Here, we combine a cheap metal with simple ligands to easily access a photoactive complex. Specifically, we synthesize the molybdenum(0) carbonyl complex Mo(CO)3(tpe) featuring the tripodal ligand 1,1,1-tris(pyrid-2-yl)ethane (tpe) in two steps with a high overall yield. The complex shows intense deep-red phosphorescence with excited state lifetimes of several hundred nanoseconds. Time-resolved infrared spectroscopy and laser flash photolysis reveal a triplet metal-to-ligand charge-transfer (3MLCT) state as the lowest excited state. Temperature-dependent luminescence complemented by density functional theory (DFT) calculations suggest thermal deactivation of the 3MLCT state via higher lying metal-centered states in analogy to the well-known photophysics of Ru(bpy)32+. Importantly, we found that the title compound is very photostable due to the lack of labilized Mo–CO bonds (as caused by trans-coordinated CO) in the facial configuration of the ligands. Finally, we show the versatility of the molybdenum(0) complex in two applications: (1) green-to-blue photon upconversion via a triplet–triplet annihilation mechanism and (2) photoredox catalysis for a green-light-driven dehalogenation reaction. Overall, our results establish tripodal carbonyl complexes as a promising design strategy to access stable photoactive complexes of nonprecious metals avoiding tedious multistep syntheses.
During the early to mid‐Miocene, benthic δ18O records indicate large ice volume fluctuations of the Antarctic ice sheet (AIS) on multiple timescales. Hitherto, research has mainly focused on how CO2 ...and insolation changes control an equilibrated AIS. However, transient AIS dynamics remain largely unexplored. Here, we study Miocene AIS variability, using an ice sheet‐shelf model forced by climate model output with various CO2 levels and orbital conditions. Besides equilibrium simulations, we conduct transient experiments, gradually changing the forcing climate state over time. We show that transient AIS variability is substantially smaller than equilibrium differences. This reduces the contribution of the AIS to δ18O fluctuations by more than two thirds on a 40‐kyr timescale, hence requiring a larger contribution by deep‐sea‐temperature variability. The growth rates are much slower than the decay rates, which ensures variability around a preferred small state. Finally, if the bedrock topography enlarges the West Antarctic land surface, AIS self‐sustenance increases.
Key Points
The contribution of transient Antarctic ice sheet variations to Miocene δ18O signals is smaller than indicated by equilibrium differences
Transient ice volume variability is centered around a preferred small state and is dependent on the timescale of the forcing
Enlarging the West Antarctic land surface increases the self‐sustenance of the Miocene Antarctic ice sheet, decreasing the variability
The international endeavour to retrieve a continuous ice core, which spans the middle Pleistocene climate transition ca. 1.2–0.9 Myr ago, encompasses a multitude of field and model-based pre-site ...surveys. We expand on the current efforts to locate a suitable drilling site for the oldest Antarctic ice core by means of 3-D continental ice-sheet modelling. To this end, we present an ensemble of ice-sheet simulations spanning the last 2 Myr, employing transient boundary conditions derived from climate modelling and climate proxy records. We discuss the imprint of changing climate conditions, sea level and geothermal heat flux on the ice thickness, and basal conditions around previously identified sites with continuous records of old ice. Our modelling results show a range of configurational ice-sheet changes across the middle Pleistocene transition, suggesting a potential shift of the West Antarctic Ice Sheet to a marine-based configuration. Despite the middle Pleistocene climate reorganisation and associated ice-dynamic changes, we identify several regions conducive to conditions maintaining 1.5 Myr (million years) old ice, particularly around Dome Fuji, Dome C and Ridge B, which is in agreement with previous studies. This finding strengthens the notion that continuous records with such old ice do exist in previously identified regions, while we are also providing a dynamic continental ice-sheet context.
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