Extremely thin-absorber solar cells offer low materials utilization and simplified manufacture but require improved means to enhance photon absorption in the active layer. Here, we report ...enhanced-absorption colloidal quantum dot (CQD) solar cells that feature transfer-stamped solution-processed pyramid-shaped electrodes employed in a hierarchically structured device. The pyramids increase, by up to a factor of 2, the external quantum efficiency of the device at absorption-limited wavelengths near the absorber band edge. We show that absorption enhancement can be optimized with increased pyramid angle with an appreciable net improvement in power conversion efficiency, that is, with the gain in current associated with improved absorption and extraction overcoming the smaller fractional decrease in open-circuit voltage associated with increased junction area. We show that the hierarchical combination of micron-scale structured electrodes with nanoscale films provides for an optimized enhancement at absorption-limited wavelengths. We fabricate 54.7° pyramid-patterned electrodes, conformally apply the quantum dot films, and report pyramid CQD solar cells that exhibit a 24% improvement in overall short-circuit current density with champion devices providing a power conversion efficiency of 9.2%.
The electroreduction of carbon dioxide (CO2RR) to valuable chemicals is a promising avenue for the storage of intermittent renewable electricity. Renewable methane, obtained via CO2RR using renewable ...electricity as energy input, has the potential to serve as a carbon-neutral fuel or chemical feedstock, and it is of particular interest in view of the well-established infrastructure for its storage, distribution, and utilization. However, CO2RR to methane still suffers from low selectivity at commercially relevant current densities (>100 mA cm–2). Density functional theory calculations herein reveal that lowering *CO2 coverage on the Cu surface decreases the coverage of the *CO intermediate, and then this favors the protonation of *CO to *CHO, a key intermediate for methane generation, compared to the competing step, C–C coupling. We therefore pursue an experimental strategy wherein we control local CO2 availability on a Cu catalyst by tuning the concentration of CO2 in the gas stream and regulate the reaction rate through the current density. We achieve as a result a methane Faradaic efficiency (FE) of (48 ± 2)% with a partial current density of (108 ± 5) mA cm–2 and a methane cathodic energy efficiency of 20% using a dilute CO2 gas stream. We report stable methane electrosynthesis for 22 h. These findings offer routes to produce methane with high FE and high conversion rate in CO2RR and also make direct use of dilute CO2 feedstocks.
The optoelectronic tunability offered by colloidal quantum dots (CQDs) is attractive for photovoltaic applications but demands proper band alignment at electrodes for efficient charge extraction at ...minimal cost to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high quality CQD solids. We report robust self-assembled monolayers (R-SAMs) that enable us to increase the efficiency of CQD photovoltaics. Only by developing a process for secure anchoring of aromatic SAMs, aided by deposition of the SAMs in a water-free deposition environment, were we able to provide an interface modification that was robust against the ensuing chemical treatments needed in the fabrication of CQD solids. The energy alignment at the rectifying interface was tailored by tuning the R-SAM for optimal alignment relative to the CQD quantum-confined electron energy levels. This resulted in a CQD PV record power conversion efficiency (PCE) of 10.7% with enhanced reproducibility relative to controls.
Materials optimized for single-junction solar spectral harvesting, such as silicon, perovskites, and large-band-gap colloidal quantum dot solids, fail to absorb the considerable infrared spectral ...energy that lies below their respective band gap. Here we explore through modeling and experiment the potential for colloidal quantum dots (CQDs) to augment the performance of solar cells by harnessing transmitted light in the infrared. Through detailed balance modeling, we identify the CQD band gap that is best able to augment wafer-based, thin-film, and also solution-processed photovoltaic (PV) materials. The required quantum dots, with an excitonic peak at 1.3 μm, have not previously been studied in depth for solar performance. Using computational studies we find that a new ligand scheme distinct from that employed in better-explored 0.95 μm band gap PbS CQDs is necessary; only via the solution-phase application of a short bromothiol can we prevent dot fusion during ensuing solid-state film treatments and simultaneously offer a high valence band-edge density of states to enhance hole transport. Photoluminescence spectra and transient studies confirm the desired narrowed emission peaks and reduced surface-trap-associated decay. Electronic characterization reveals that only through the use of the bromothiol ligands is strong hole transport retained. The films, when used to make PV devices, achieve the highest AM1.5 power conversion efficiency yet reported in a solution-processed material having a sub-1 eV band gap.
Colloidal quantum dot (CQD) films allow large-area solution processing and bandgap tuning through the quantum size effect. However, the high ratio of surface area to volume makes CQD films prone to ...high trap state densities if surfaces are imperfectly passivated, promoting recombination of charge carriers that is detrimental to device performance. Recent advances have replaced the long insulating ligands that enable colloidal stability following synthesis with shorter organic linkers or halide anions, leading to improved passivation and higher packing densities. Although this substitution has been performed using solid-state ligand exchange, a solution-based approach is preferable because it enables increased control over the balance of charges on the surface of the quantum dot, which is essential for eliminating midgap trap states. Furthermore, the solution-based approach leverages recent progress in metal:chalcogen chemistry in the liquid phase. Here, we quantify the density of midgap trap states in CQD solids and show that the performance of CQD-based photovoltaics is now limited by electron-hole recombination due to these states. Next, using density functional theory and optoelectronic device modelling, we show that to improve this performance it is essential to bind a suitable ligand to each potential trap site on the surface of the quantum dot. We then develop a robust hybrid passivation scheme that involves introducing halide anions during the end stages of the synthesis process, which can passivate trap sites that are inaccessible to much larger organic ligands. An organic crosslinking strategy is then used to form the film. Finally, we use our hybrid passivated CQD solid to fabricate a solar cell with a certified efficiency of 7.0%, which is a record for a CQD photovoltaic device.
This trial investigated whether an intensive lifestyle intervention to produce weight loss and increased fitness would slow loss of mobility among obese patients with type 2 diabetes. Both weight ...loss and improved fitness were associated with a decline in the rate of mobility loss.
The growing prevalence of type 2 diabetes mellitus is an ominous health threat in the United States
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,
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and globally.
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Surveillance data from the Centers for Disease Control and Prevention cite type 2 diabetes as largely a disease of aging,
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and its prevalence may escalate as the population gets older.
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,
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An insidious consequence of aging in persons with type 2 diabetes is physical disability,
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particularly the loss of mobility.
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Reduced mobility puts patients at risk for loss of independence,
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leads to muscle loss (which compromises glucose storage and clearance),
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and compromises the quality of life.
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With increasing age in . . .
The impact of weight loss intervention on disability-free life expectancy in adults with diabetes is unknown. We examined the impact of a long-term weight loss intervention on years spent with and ...without physical disability.
Overweight or obese adults with type 2 diabetes age 45-76 years (
= 5,145) were randomly assigned to a 10-year intensive lifestyle intervention (ILI) or diabetes support and education (DSE). Physical function was assessed annually for 12 years using the 36-Item Short Form Health Survey. Annual incidence of physical disability, mortality, and disability remission were incorporated into a Markov model to quantify years of life spent active and physically disabled.
Physical disability incidence was lower in the ILI group (6.0% per year) than in the DSE group (6.8% per year) (incidence rate ratio 0.88 95% CI 0.81-0.96), whereas rates of disability remission and mortality did not differ between groups. ILI participants had a significant delay in moderate or severe disability onset and an increase in number of nondisabled years (
< 0.05) compared with DSE participants. For a 60-year-old, this effect translates to 0.9 more disability-free years (12.0 years 95% CI 11.5-12.4 vs. 11.1 years 95% CI 10.6-11.7) but no difference in total years of life. In stratified analyses, ILI increased disability-free years of life in women and participants without cardiovascular disease (CVD) but not in men or participants with CVD.
Long-term lifestyle interventions among overweight or obese adults with type 2 diabetes may reduce long-term disability, leading to an effect on disability-free life expectancy but not on total life expectancy.
In any given survey, individuals are likely to differ in attitudes toward the subject matter. They also may differ in terms of the duration and persistence of attitudes, with some persons' beliefs ...being much more stable than others. For the purpose of jointly assessing attitude and temporal attitudinal stability, we propose a latent bivariate item response model. Attitudinal stability is operationalized as a construct called response consistency, which is indicated by the concordance of observed responses between two-time points. A simulation experiment assesses the parameter recovery of the proposed model. A real data analysis example uses data collected from a study on folklore beliefs about diabetes (563 individuals from multiple rural communities in North Carolina). On two different occasions, the individuals in the sample completed a 31-item common-sense model of diabetes inventory, which measures the congruence of their beliefs with a biomedical model. Results from the simulation study showed that the model parameters and factor correlation in the latent bivariate IRT model overall recovered well. Results from the real data analysis demonstrated the saliency of the construct. A weak association between having beliefs congruent with the biomedical model and response consistency across the two administrations was found.
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