Power/Performance Bits: Dec. 6

Perovskites for data storage

Scientists at EPFL developed a new perovskite material whose magnetic order can be rapidly changed without disrupting it due to heating that could potentially be used to build next-generation hard drives.

“We have essentially discovered the first magnetic photoconductor,” said Bálint Náfrádi, a postdoc at EPFL. This new crystal structure combines the advantages of both ferromagnets, whose magnetic moments are aligned in a well-defined order, and photoconductors, where light illumination generates high density free conduction electrons.

Single crystals of the perovskite developed in this study; on the right a diagram showing the melting of the ferromagnetic state. (Source: M. Spina, E. Horváth/EPFL)

The combination of the two properties produced an entirely new phenomenon: the “melting” of magnetization by photo-electrons, which are electrons that are emitted from a material when light hits it. In the new perovskite material, a simple red LED – much weaker than a laser pointer – is enough to disrupt, or “melt” the material’s magnetic order and generate a high density of travelling electrons, which can be freely and continuously tuned by changing the light’s intensity. The timescale for shifting the magnetic in this material is also very fast, needing only quadrillionths of a second.

“This study provides the basis for the development of a new generation of magneto-optical data storage devices,” according to Náfrádi. “These would combine the advantages of magnetic storage – long-term stability, high data density, non-volatile operation and re-writability – with the speed of optical writing and reading.”

Large perovskite solar cells

Engineers at Australia’s University of New South Wales hit a new record for efficiency with the largest perovskite solar cells to date.

The 12.1% efficiency rating was for a 16 cm2 perovskite solar cell, the largest single perovskite photovoltaic cell certified with the highest energy conversion efficiency. The new cell is at least 10 times bigger than the current certified high-efficiency perovskite solar cells on record.

The team has also achieved an 18% efficiency rating on a 1.2 cm2 single perovskite cell, and an 11.5% for a 16 cm2 four-cell perovskite mini-module.

“The versatility of solution deposition of perovskite makes it possible to spray-coat, print or paint on solar cells,” said Anita Ho-Baillie, a Senior Research Fellow at the Australian Centre for Advanced Photovoltaics. “The diversity of chemical compositions also allows cells be transparent, or made of different colours. Imagine being able to cover every surface of buildings, devices and cars with solar cells.”

However, perovskites are currently prone to fluctuating temperatures and moisture, making them last only a few months without protection.

“This is a very hot area of research, with many teams competing to advance photovoltaic design,” said Ho-Baillie. “Perovskites came out of nowhere in 2009, with an efficiency rating of 3.8%, and have since grown in leaps and bounds. These results place UNSW amongst the best groups in the world producing state-of-the-art high-performance perovskite solar cells. And I think we can get to 24% within a year or so.”

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