When ferroelectric materials like KBNNO undergo changes in temperature, their dipoles misalign, which induces an electric current. Electric charge also accumulates according to the direction the dipoles point. Deforming the material causes certain regions to attract or repel charges, again generating a current.
The experiments showed that while KBNNO is reasonably good at generating electricity from heat and pressure, it isn't quite as good as other perovskites. However, the researchers claim they can modify the composition of KBNNO to improve its pyroelectric and piezoelectric properties.
"It is possible that all these properties can be tuned to a maximum point," said researcher Yang Bai from the University of Oulu.
Within the next year, Bai hopes to build a prototype multi-energy-harvesting device. "This will push the development of the IoT and smart cities, where power-consuming sensors and devices can be energy sustainable," he said.
At the same time, NREL researchers are said to have determined that recombination in other parts of a methylammonium perovskite film isn't as important as what's happening on its surface.
Recombination is when sunlight creates mobile electrons whose movement generates power, but upon encountering defects can slip into a non-productive process. This process reduces the efficiency of a solar cell.
According to the scientists, for the cell to be efficient, the recombination must occur slowly.
The studied surface recombination in single-crystal and polycrystalline films using transient reflection spectroscopy.
"What's important is to know where the recombination is coming from," said researcher Matthew Beard. "There are multiple sources of possible recombination. In order to improve your device, you're asked to get rid of all non-radiative recombination. Typically, people forget about surfaces. They think about grain boundaries, bulk defects and so forth."
Beard claims the research determined surface recombination emerged as an obstacle to overcome. Surface recombination directly affects the performance of a photovoltaic device.
A fast surface recombination can be used to design photodetectors, while lasers and LEDs require a slower speed.
