Thin-film solar cells require little energy and material to produce and therefore have a very small environmental footprint. In addition to the well-known and market-leading silicon solar cells, there are also thin-film solar cells, e.g. based on copper, indium, gallium and selenium, known as CIGS cells. CIGS thin films can even be applied to flexible substrates.

Now, experts from HZB and Humboldt University Berlin, have developed a new tandem solar cell that combines a bottom cell made of CIGS with a top cell based on perovskite. By improving the contact layers between the top and bottom cells, they were able to increase the efficiency to 24.6 %. This is the current world record, as certified by the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany.

This record cell was the result of a successful team effort: the top cell was fabricated by TU Berlin master’s student Thede Mehlhop under the supervision of Stefan Gall. The perovskite absorber layer was produced in the joint laboratory of HZB and Humboldt University of Berlin. The CIGS sub-cell and contact layers were fabricated by HZB researcher Guillermo Farias Basulto. He also used the high-performance cluster system KOALA, which enables the deposition of perovskites and contact layers in vacuum at HZB.

‘At HZB, we have highly specialised laboratories and experts who are top performers in their fields. With this world record tandem cell, they have once again shown how fruitfully they work together,’ says Prof. Rutger Schlatmann, spokesman for the Solar Energy Department at HZB.

The record announced today is not the first world record at HZB: HZB teams have already achieved world record values for tandem solar cells several times, most recently for silicon-perovskite tandem solar cells, but also with the combination CIGS-perovskite.

We are confident that CIGS-perovskite tandem cells can achieve much higher efficiencies, probably more than 30%,” says Prof. Rutger Schlatmann.

“In our analysis focusing on Los Angeles County, unexpected traffic delays beyond the usual congestion led to a 1% increase in fast food visits. That might not sound like a lot, but it’s equivalent to 1.2 million more fast food visits per year in LA County alone. We describe our results as being modest but meaningful in terms of potential for changing unhealthy food choices,” said study author Becca Taylor, assistant professor in the Department of Agricultural and Consumer Economics, part of the College of Agricultural, Consumer and Environmental Sciences at Illinois.

Taylor and her co-authors had access to daily highway traffic patterns over more than two years in Los Angeles, along with data showing how many cell phone users entered fast-food restaurants in the same time period. With these data, the team created a computational model showing a causal link between unexpected traffic slow-downs and fast food visits.

This pattern held at various time scales, including 24-hour cycles and by the hour throughout a given day. When analyzed by the day, traffic delays of just 30 seconds per mile were enough to spike fast-food visits by 1%.

“It might not be intuitive to imagine what a 30-second delay per mile feels like,” Taylor said. “I think of it as the difference between 10 a.m. traffic and 5 p.m. traffic.”

When the researchers broke the day into hour-long segments, they found a significantly greater number of fast food visits when traffic delays hit during the evening rush hour. At the same time, grocery store visits declined slightly.

“If there’s traffic between 5 and 7 p.m., which happens to be right around the evening meal time, we see an increase in fast food visits,” Taylor said. “Drivers have to make a decision about whether to go home and cook something, stop at the grocery store first, or just get fast food.”

Considering every major city has both traffic and fast food restaurants lining highway feeder roads, it’s not a stretch to extrapolate the pattern beyond Los Angeles. Taylor and her co-authors say the link between traffic and unhealthy food choices is just one more reason policymakers around the country and the globe should prioritize infrastructure reforms to ease congestion.

“Our results contribute to the literature suggesting time constraints are really important to the food choices people make. Any policies aimed at loosening time constraints — and traffic is essentially lost time — could help battle unhealthy eating,” Taylor said. “That could mean improvements in infrastructure to mitigate traffic congestion, expanding public transport availability, and potentially increasing work from home opportunities.”

The finding, reported in the science journal Geochimica et Cosmochimica Acta, is significant because the data reported by the study support the idea that water arrived towards the final stages of Earth’s development into a planet from dust and gas, what geologists refer to as late accretion.

Scientists seek to learn when the constituent materials necessary for life appeared so that they can understand how and when life began. According to present scientific understanding, at least three necessary ingredients are essential to kick-start life. These are water, energy and a soup of organic chemicals known as CHNOPS — scientific shorthand for carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.

“When water was delivered to the planet is a major unanswered question in planetary science,” said Katherine Bermingham, an associate professor in the Department of Earth and Planetary Sciences in the Rutgers School of Arts and Sciences and lead author of the study. “If we know the answer, we can better constrain when and how life developed.”

Bermingham is a cosmogeochemist, a scientist who studies the chemical composition of matter in the solar system, particularly focusing on the origin and evolution of the solar system and its rocky planets by analyzing Earth rocks and extraterrestrial materials such as meteorites.

Using thermal ionization mass spectrometry and a new analytical method the team developed, Bermingham and colleagues studied isotopes of the element molybdenum. An isotope is a form of an element with the same number of protons but a different number of neutrons. This allows it to share the same chemical properties while having a different atomic mass.

“The molybdenum isotopic composition of Earth rocks provides us with a special window into events occurring around the time of Earth’s final core formation, when the last 10% to 20% of material was being assembled by the planet. This period is thought to coincide with the Moon’s formation,” Bermingham said.

They extracted molybdenum from meteorite samples obtained from the National Museum of Natural History of the Smithsonian Institution. The scientific community has divided meteorites into two general groups — the first, “CC,” with constituent elements suggesting the meteorites formed in the outer, presumably wetter, Solar System. The second group, “NC,” has characteristics indicating its meteorites formed in the inner, presumably drier, solar system. This study focused on samples that belong to the NC group.

They compared the molybdenum isotopic composition of these meteorites to Earth rocks from Greenland, South Africa, Canada, the United States and Japan collected by field geologists. The molybdenum in these rocks is generally considered to have been added to Earth during the time the Moon was formed, which is when final core formation occurred. This is precisely when the team wanted to search for the origins of water.

“Once we gathered the different samples and measured their isotopic compositions, we compared the meteorites signatures with the rock signatures to see if there was a similarity or a difference,” Bermingham said. “And from there, we drew inferences.”

The analyses showed that the Earth rocks they studied were more similar to meteorites sourced from the inner solar system meteorites (NC) rather than meteorites sourced from the outer solar system (CC).

“We have to figure out from where in our solar system Earth’s building blocks — the dust and the gas — came and around when that happened,” Bermingham said. “That’s the information needed to understand when the stage was set for life to begin.”

Since the chemical composition of the Earth rocks they studied matches that of the presumed inner solar system (NC) meteorites, the scientists concluded that the Earth had not received as much water from the Moon-forming event as previously thought. The finding is significant, Bermingham said, because a popular theory of water delivery is that a significant amount of the Earth’s water was added when the Moon was formed.

This research, however, showed that a substantial amount of water likely did not come during this period of growth. Instead, the data support the interpretation that water was delivered to Earth in smaller portions after the Moon was formed, far later during Earth’s formation.

“Our results suggest that the Moon-forming event was not a major supplier of water, unlike what has been thought previously,” Bermingham said. “These findings, however, permit a small amount of water to be added after final core formation, during what is called late accretion.”

Other Rutgers authors of the study include Linda Godfrey, an assistant research professor, and laboratory researcher Hope Tornebene, both of the Department of Earth and Planetary Sciences.

Program for teens adapted to seniors

The O’stress program is based on DeStress for Success, an innovative program created by the Centre for Studies on Human Stress to help teens deal with the stress of transitioning to high school.

In a groundbreaking study led by Sonia Lupien, the Centre’s director, published in Neuroscience in 2013, DeStress for Success was shown to decrease cortisol levels and depressive symptoms in participating teens who were experiencing strong negative emotions at the start of the school year.

Since then, DeStress for Success has been adapted in partnership with Plusquellec’s team for several populations, including teens at high risk for behavioural problems (2016) and young people with autism spectrum disorder (2018).

Countering emotional contagion

In her doctoral research under the supervision of Université de Montréal professors Pierrich Plusquellec and Sébastien Grenier, Marie-Josée Richer adapted DeStress for Success to the specific needs of seniors.

“Aging, like adolescence but for different reasons, is a particularly sensitive period when individuals are more vulnerable to chronic stress and its consequences,” Plusquellec noted.

O’stress incorporates elements relevant to aging, social relationships and, in particular, emotional contagion, the tendency to get caught up in the emotions of others. According to a recent study by the same researchers, emotional contagion is a significant factor in psychological distress among seniors. An educational component on emotional contagion was therefore included in the O’stress program to help participants recognize and manage this dynamic on a daily basis.

O’stress uses a variety of approaches including small-group workshops to help seniors identify symptoms of stress and release that energy through activities such as bopping to The Beatles’ “Twist and Shout.” Participants also analyze their social network to identify sources of support, pressure and emotional contagion, and then problem-solve to find solutions.

The success of O’stress highlights the enormous potential of short, accessible interventions to counteract the harmful effects of chronic stress in the elderly.

“By demystifying stress and its effects, and then teaching effective techniques for coping with that stress, we equip participants to strengthen their resilience and overall well-being,” said Richer.

The research team now hopes to expand the O’stress program and evaluate its effectiveness in other contexts and populations. Their work could also inspire similar interventions in the areas of mental health and aging.