“There’s a growing trend of making anything we interact with and touch from materials that are dynamic and responsive to the environment,” Sahin says. “We found a way to develop a material that is water-resistant yet, at the same time, equipped to harness water to deliver the force and motion needed to actuate mechanical systems.”

The research was published online May 21 in Advanced Materials Technologies.

Most traditional robotic systems are hard, that is, composed of metallic structures that require a computer to function. Soft robots are created with materials that don’t use a rigid skeleton or electricity to provide mechanical strength. They are simpler to make and less expensive than hard robots, more capable of complex motions and safer to use around humans.

The material developed by the Columbia researchers is made of a novel combination of spores — units produced by bacteria that are often used as food supplements — and adhesives. They provide an alternative to materials, such as synthetic polymers, commonly used in hard actuators and are better than the gels more generally used in soft actuators. Compared to the new material, gels are slower to respond, cannot generate high power or force and usually fail in direct contact with water.

Although the individual spores are water-resistant, they are so tiny that they must be bound together via a photochemical process in which high-intensity light instantly glues them together into a composite material. The researchers employ an inexpensive, commercially available UV light that is used in salons to cure nail polish.

Once dry, the material is stacked in layers to form a microscopic structure that expands or contracts with humidity or moisture, producing the force and motion of mechanical work.

“It’s like making sheets or surfaces from sand,” says postdoctoral research scientist Onur Cakmak, lead author of the study and a member of the research team. “The material is very granular.”

Guided by the pattern design, the porous composite can bend, fold and unfold in response to humidity or water. This gives the soft actuators agility and adaptability to their surroundings, much like organisms in nature. The ability to be patterned, says Cakmak, “is essential if you want to make useful systems out of these materials.”

Sahin sees many potential applications for the new material, from practical items to artistic creations. Actuators made from the water-resistant, humidity-responsive composite could be used to open a building’s windows when the humidity rises too high. The material could also be added to fabric in athletic clothing to help sweat evaporate faster. “We’re providing material for designers to work with and get their ideas realized quickly,” Sahin says.

Applications meant to function for years still need further testing, he adds, but those designed for shorter periods might already be ready for use.

“As we work on this, we also learn many other possible uses, some related to design and others to materials that could be part of the products around us,” says Sahin. “Those could be places where the impact of this could be sooner.”

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Materials provided by Columbia University. Note: Content may be edited for style and length.

Over the last decade, Colorado State University researchers have led pioneering studies into improving the performance and cost of solar energy by fabricating and testing new materials that extend beyond the capabilities of silicon. They have focused on a material that shows promise for replacing silicon, called cadmium telluride.

In collaboration with partners at Loughborough University in the United Kingdom, researchers at CSU’s National Science Foundation-supported Next Generation Photovoltaics Center have reported a key breakthrough in how the performance of cadmium telluride thin-film solar cells is improved even further by the addition of another material, selenium. Their results were published in the journal Nature Energy earlier this month and are the subject of a “News and Views” article.

“Our paper goes right to the fundamental understanding of what happens when we alloy selenium to cadmium telluride,” said Kurt Barth, a director of the Next Generation Photovoltaics Center and an associate research professor in the Department of Mechanical Engineering.

Until now, it was not well understood why the addition of selenium has clocked record-breaking cadmium telluride solar cell efficiency — the ratio of energy output to light input — of just over 22 percent. Together with CSU collaborators W.S. Sampath and Amit Munshi, Barth and an international team have solved that mystery. Their experiments revealed that selenium overcomes the effects of atomic-scale defects in cadmium telluride crystals, providing a new path for more widespread, less expensive solar-generated electricity.

The cadmium telluride thin films that the CSU team makes in the lab use 100 times less material than conventional silicon solar panels. They are thus easier to manufacture, and they absorb sunlight at nearly the ideal wavelength. Electricity produced by cadmium telluride photovoltaic cells is the lowest-cost available in the solar industry, undercutting fossil fuel-based sources in many regions of the world.

According to the paper, electrons generated when sunlight hits the selenium-treated solar panel are less likely to be trapped and lost at the material’s defects, located at the boundaries between crystal grains as they are grown. This increases the amount of power extracted from each solar cell. Working with materials fabricated at CSU via advanced deposition methods, the team discovered this unexpected behavior by measuring how much light is emitted from selenium-containing panels.

As selenium is not evenly distributed across the panels, they compared luminescence emitted from areas where there was little-to-no selenium present and areas where the selenium was very concentrated.

“Good solar cell material that is defect-free is very efficient at emitting light, and so luminesces strongly,” said Tom Fiducia, the paper’s lead author and a Ph.D. student at the University of Loughborough, working with Professor Michael Walls. “It is strikingly obvious when you see the data that selenium-rich regions luminesce much more brightly than the pure cadmium telluride, and the effect is remarkably strong.”

The National Science Foundation has supported the work of CSU’s Next Generation Photovoltaics Center since 2009.

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Materials provided by Colorado State University. Original written by Anne Manning. Note: Content may be edited for style and length.

The team published their findings on May 22, 2019 in the journal Energy & Environmental Science.

Hybrid halide semiconductors are materials that consist of an inorganic framework housing organic cations. They show unique material properties that are not found in organic or inorganic materials alone.

A subclass of these materials, called hybrid halide perovskites, have attracted a lot of attention as promising materials for next generation solar cells and LED devices because of their exceptional optoelectronic properties and inexpensive fabrication costs. However, hybrid perovskites are not very stable and contain lead, making them unsuitable for commercial devices.

Seeking alternatives to perovskites, a team of researchers led by Kesong Yang, a nanoengineering professor at the UC San Diego Jacobs School of Engineering, used computational tools, data mining and data screening techniques to discover new hybrid halide materials beyond perovskites that are stable and lead-free. “We are looking past perovskite structures to find a new space to design hybrid semiconductor materials for optoelectronics.” Yang said.

Yang’s team started by going through the two largest quantum materials databases, AFLOW and The Materials Project, and analyzing all compounds that were similar in chemical composition to lead halide perovskites. Then they extracted 24 prototype structures to use as templates for generating hybrid organic-inorganic materials structures.

Next, they performed high-throughput quantum mechanics calculations on the prototype structures to build a comprehensive quantum materials repository containing 4,507 hypothetical hybrid halide compounds. Using efficient data mining and data screening algorithms, Yang’s team rapidly identified 13 candidates for solar cell materials and 23 candidates for LEDs out of all the hypothetical compounds.

“A high-throughput study of organic-inorganic hybrid materials is not trivial,” Yang said. It took several years to develop a complete software framework equipped with data generation, data mining and data screening algorithms for hybrid halide materials. It also took his team a great deal of effort to make the software framework work seamlessly with the software they used for high-throughput calculations.

“Compared to other computational design approaches, we have explored a significantly large structural and chemical space to identify novel halide semiconductor materials,” said Yuheng Li, a nanoengineering PhD candidate in Yang’s group and the first author of the study. This work could also inspire a new wave of experimental efforts to validate computationally predicted materials, Li said.

Moving forward, Yang and his team are using their high-throughput approach to discover new solar cell and LED materials from other types of crystal structures. They are also developing new data mining modules to discover other types of functional materials for energy conversion, optoelectronic and spintronic applications.

Behind the scenes: SDSC’s ‘Comet’ supercomputer powers the research

Yang attributes much of his project’s success to the utilization of the Comet supercomputer at UC San Diego’s San Diego Supercomputer Center (SDSC). “Our large-scale quantum mechanics calculations required a large number of computational resources,” he explained. “Since 2016, we have been awarded with computing time — some 3.46 million core-hours on Comet, which made the project possible.”

While Comet powered the simulations in this study, Yang said that SDSC staff also played a crucial role in his research. Ron Hawkins, SDSC’s director of industry relations, and Jerry Greenberg, a computational research specialist with the Center, ensured that adequate support was provided to Yang and his team. The researchers especially relied on the SDSC staff for the study’s compilation and installation of computational codes on Comet, which is funded by the National Science Foundation.

Yang, who was connected with SDSC via the Center’s Triton Shared Computing Cluster (TSCC) campus cluster at UC San Diego, said that Comet not only saved them time. “The value of these awarded computing resources is about $115,600, which also saved our project a great deal of money.”

This work was supported by the Global Research Outreach (GRO) Program of Samsung Advanced Institute of Technology (award number 20164974) and the National Science Foundation (ACI-1550404). The ab-initio molecular dynamics calculations used computational resources supplied by the Department of Defense High Performance Computing Modernization Program (HPCMP).