3-in-1 renewable material can harness energy from the Sun, heat and movement

Flexible Perovskite Solar Cell. Image Credits: National Physical Laboratory
3-in-1 RENEWABLE MATERIAL

It’s no surprise that renewable energy is a key issue with keeping the planet sustainable – fossil fuels are running out and climate change is a serious problem. Solar panels, wind farms and even the idea of space lasers have been used to mitigate this.

There is constantly a need for more efficient renewable energy.

Cue perovskites, or specifically, the crystals in a perovskite structure that have been known to extract energy from one or two of the sunlight, heat and movement sources, but not all three at the same time. This was, of course, until Researchers from the Finnish University of Oulu discovered KBNNO.

Perovskite structure of CH3NH3PbI3
Perovskite structure of CH3NH3PbI3 Image Credits: Nature
THE GENERAL STRUCTURE OF A PEROVSKITE

Perovskites were first discovered by Gustav Rose in the Ural Mountains and are named after the mineralogist Lev Perovski.

Perovskites follow the formula ABO3. In the case of KBNNO, A = Potassium and B = Nobelium. Generally speaking, however, A can be an alkali metal or a rare earth element (lanthanides, scandium and yttrium) and B is generally a transition metal.

(1-x)KNbO3-xBaNi1/2Nb1/2O3-δ, or KBNNO for short, is the name of this potential game changer. It is created by modifying KNbO3 crystals with barium and nickel.

These compounds are ferroelectric, meaning they’re full of small electric dipoles. A dipole is essentially a magnet, containing a north and a south pole. Perovskites have what’s known as a permanent dipole moment, meaning that they don’t need an external influence to give the dipoles their magnetic properties.

Once the perovskites have been heated, the dipoles point in random directions which induces an electric current. Once the temperature drops back down, the dipoles align themselves and point in the same direction again. This is called pyroelectricity – when a temperature change induces a temporary voltage.

This study was the first time that the photovoltaic and ferroelectric properties were studied at temperatures above room temperature,” says Dr. Yang Bai, one of the researchers at the University of Oulu.

KBNNO vs OTHER PEROVSKITES

KBNNO was found to be suitable at producing an electric current from light, whereas other perovskites had better piezoelectric (movement) and pyroelectric properties. Regardless, they’ve suggested that altering the balance of elements will rectify this.

The conclusion of the study, found on the Applied Physics Letters website, explained that altering the potassium to nobelium ratio still gave positive results for ferroelectric, pyroelectric and piezoelectric properties. It also explains that further compositional optimisation and device fabrication is currently still on-going.

In 2009, perovskites were only 3% effective at converting sunlight into electricity and in only 7 years, that figure has increased to over 20%.  Dr. Alexander Weber-Bargioni and a team of researchers, in 2016, found a theoretical max value of 34%.

Perovskites are already being used in solar cells. The perovskite structure of methylammonium lead halides are cheap, easy to manufacture and shows high photovoltaic properties.

Unfortunately, Dr. Bai’s study found that this perovskite isn’t the most efficient at extracting energy from sunlight, heat and movement. This doesn’t hinder the results whatsoever, as the selling point is that it’s been proven to be able to extract energy from all 3 of these sources simultaneously. This discovery, whilst in its early days, has the real possibility of completely eliminating the need for the standard lithium battery.

“This will push the development of the Internet of Things and smart cities, where power-consuming sensors and devices can be energy sustainable,” claims Dr. Bai.

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Source Applied Physics Letters Nature

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