Power/Performance Bits: Sept. 3

Nylon capacitor
Researchers at the Max Planck Institute for Polymer Research, Johannes Gutenberg University of Mainz, and Lodz University of Technology developed a way to fabricate ferroelectric nylon thin-film capacitors.

Nylons consist of a long chain of polymers and, along with use in textiles, exhibit ferroelectric properties. However, electronic applications have been limited as there was no way to create high-quality thin films of ferroelectric nylon by solution processing due to the strong tendency of nylon chains to form hydrogen bonds.

The team’s new process for creating these thin films involves dissolving nylon in a mixture of trifluoroacetic acid and acetone and solidifying it again in vacuum.

The team’s nylon films measured a few 100 nanometers thick. “Using this method, we have produced extremely smooth thin-films. This is very important because it prevents electrical break down of for example capacitors and destroying the electronic circuits. At the same time, the smoothness allows for having transparent thin-films and eventually transparent electronic devices,” said Kamal Asadi, group leader at the MPI-P.

The new nylon capacitors were subjected to extended stress cycles and remained robust after millions of operation cycles. The team sees the nylon films as a component for flexible electronics such as in electronic clothing, providing a multi-functional fabric that could generate electricity from body movement.

Singlet fission
Researchers at Columbia University, University of New South Wales, and Brookhaven National Laboratory created organic molecules capable of generating two excitons per photon of light, a process called singlet fission they say could be used to increase the efficiency of solar cells.

“We have developed a new design rule for singlet fission materials,” said Luis Campos, an associate professor of chemistry at Columbia. “This has led us to develop the most efficient and technologically useful intramolecular singlet fission materials to date. These improvements will open the door for more efficient solar cells.”

Campos explained that in modern solar panels, one photon of light generates one exciton, which can be converted to electric current. Some molecules, however, can generate two excitons and could potentially form the next generation of solar panels.

Magnetic field data that shows the formation and decay of the excitons generated by singlet fission. (Credit: A. Asadpoor Darvish, McCamey Lab)

Unfortunately, the two excitons only exist for a very short period – tens of nanoseconds – making them difficult to harvest. The team’s organic molecules can generate two excitons that last for much longer.

“Intramolecular singlet fission has been demonstrated by our group and others, but the resulting excitons were either generated very slowly, or they wouldn’t last very long,” Campos said. “This work is the first to show that singlet fission can rapidly generate two excitons that can live for a very long time. This opens the door to fundamentally study how these excitons behave as they sit on individual molecules, and also to understand how they can be efficiently put to work in devices that benefit from light-amplified signals.”

The team said that beyond solar, singlet fission could find use in photocatalytic processes in chemistry, sensors, and imaging, as these excitons can be used to initiate chemical reactions.

Aqueous zinc battery
Researchers at the City College of New York created a rechargeable manganese dioxide zinc battery that breaks the previous voltage barriers seen in earlier aqueous zinc batteries. This could help it compete against lithium-ion batteries.

“The voltage of current commercially available alkaline MnO2|Zn batteries is around 1.2-1.3V, and this has been considered low compared to Li-ion which has a voltage >3V,” said Gautam G. Yadav, a senior research associate at the Energy Institute at CCNY.

The alkaline MnO2|Zn battery has a voltage of 2.45-2.8V. To break the 2V barrier in aqueous zinc chemistry, the team interfacially engineered two different aqueous electrolytes that deliver the theoretical capacity (308mAh/g) reversibly for many cycles.

Yadav notes that the problems with lithium-ion include flammability, toxic elements, and geopolitically sensitive mining and manufacturing.

“This has put the United States at a tremendous disadvantage and has lost its lead in energy storage industry, when in the past it was a world leader,” Yadav added. “With Mn and Zn being widely available elements, and with the U.S. being rich with them as well, it allows the U.S. to compete again. The manufacturing cost of these batteries will also be low, so it can kick start the growth of the energy storage industry in the U.S.”