The ultimate energy harvesting material

February 08, 2017 // By Jean-Pierre Joosting
Researchers from the University of Oulu in Finland have found that a mineral with the perovskite crystal structure has the right properties to extract energy from multiple sources at the same time – ideal for helping power portable and wearable gadgets, from biometric sensors to smart watches

Perovskites are a family of minerals, many of which have shown promise for harvesting one or two types of energy at a time – but not simultaneously. One family member may be good for solar cells, with the right properties for efficiently converting solar energy into electricity. Meanwhile, another is adept at harnessing energy from changes in temperature and pressure, which can arise from motion, making them so-called pyroelectric and piezoelectric materials, respectively.

Other researchers have developed devices that can harness multiple forms of energy, but they require multiple materials, adding bulk to what's supposed to be a small and portable device.

In Applied Physics Letters, Yang Bai and his colleagues at the University of Oulu explain their research on a specific type of perovskite called KBNNO, which may be able to harness many forms of energy. Like all perovskites, KBNNO is a ferroelectric material, filled with tiny electric dipoles analogous to tiny compass needles in a magnet.

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.

Previous researchers have studied KBNNO's photovoltaic and general ferroelectric properties, but they did so at temperatures a couple hundred degrees below freezing, and they didn't focus on properties related to temperature or pressure. The new study represents the first time anyone has evaluated all of these properties at once above room temperature, Bai said.