Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Light provides spin

19.09.2018

Physicists at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have proven that incoming light causes the electrons in warm perovskites to rotate thus influencing the direction of the flow of electrical current. They have thus found the key to an important characteristic of these crystals, which could play an important role in the development of new solar cells.

Efficiency from spinning electrons


The sun plays an important role in the use of renewable energy sources. Its radiation energy provides heat and the light it provides can be converted into electricity thanks to photovoltaics. Perovskites, which are crystalline compounds that can be simply manufactured using chemical processes, have been considered a promising means of using the power of sunlight cost effectively for several years now. Under laboratory conditions, prototypes have achieved surprising levels of efficiency.

There is little knowledge about precisely why perovskites are so powerful. ‘Two factors are decisive for generating electrical energy cost-efficiently from sunlight’, says Dr. Daniel Niesner from the Chair of Solid State Physics at FAU. ‘One the one hand, the light must excite as many electrons as possible in a layer that’s as thin as possible. On the other, the electrons must be able to flow as freely as possible to the electrodes that pick up the current.’

Researchers suspect that perovskites make particularly good use of the rotation of electrons for efficient current flow. ‘Each electron has ‘spin’, similar to the intrinsic rotation of a billiard ball’, explains Niesner. ‘As is the case with billiard balls, where left-hand or right-hand spin when they are hit with the cue leads to a curved path on the table, scientists have suspected that rotation and forward movement in electrons in perovskites could also be linked.’

Orderly atomic structure

Physicists at FAU in Erlangen have now confirmed this suspicion for the first time. In their experiments, they used a laser whose light also has spin or a direction of rotation. The result: If a crystal is exposed to light with a left-hand spin, the electrons move to the left. If the direction of the light is reversed, the direction of the flow of electrons also reverses. ‘The experiments clearly demonstrate that the direction of rotation of the electrons and the direction of flow of current are linked.’

Up to now, scientists presumed that the atomic structure of perovskites was too ‘orderly’ for such behaviour. In actual fact, experiments with cooled perovskite crystals show only a very weak link between the direction of rotation of the electrons and the direction of current flow. ‘This changes, however, when the crystals are heated to room temperature because the movement of the atoms leads to fluctuating deviations of the highly-ordered structure’, says Nieser.

‘The heat enables the crystals of perovskite to link the direction of rotation and flow of the electrons. A ‘normal’ crystal couldn’t do that.’

The discovery of the connection between heat and spin in electrons means that the FAU researchers have uncovered a vital aspect of the unusual flow of current in perovskites. Their work could contribute to improving the understanding of the high energy efficiency of these crystals and to developing new materials for photovoltaics in the future.

Wissenschaftliche Ansprechpartner:

Further information
Dr. Daniel Niesner
Phone: +49 9131 8528403
daniel.niesner@fau.de

Originalpublikation:

The results have now been published in the renowned journal ‘Proceedings of the National Academy of Sciences’ (doi: 10.1073/pnas.1805422115 – ‘Structural fluctuations cause spin-split states in tetragonal (CH3NH3)PbI3: Experimental evidence from circular photogalvanic effect’, ‘Proceedings of the National Academy of Sciences’).

Dr. Susanne Langer | idw - Informationsdienst Wissenschaft
Further information:
http://www.fau.de/

More articles from Physics and Astronomy:

nachricht Physics: Not everything is where it seems to be
15.10.2018 | Universität Innsbruck

nachricht Disrupting crystalline order to restore superfluidity
12.10.2018 | Universität Hamburg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Storage & Transport of highly volatile Gases made safer & cheaper by the use of “Kinetic Trapping"

Augsburg chemists present a new technology for compressing, storing and transporting highly volatile gases in porous frameworks/New prospects for gas-powered vehicles

Storage of highly volatile gases has always been a major technological challenge, not least for use in the automotive sector, for, for example, methane or...

Im Focus: Disrupting crystalline order to restore superfluidity

When we put water in a freezer, water molecules crystallize and form ice. This change from one phase of matter to another is called a phase transition. While this transition, and countless others that occur in nature, typically takes place at the same fixed conditions, such as the freezing point, one can ask how it can be influenced in a controlled way.

We are all familiar with such control of the freezing transition, as it is an essential ingredient in the art of making a sorbet or a slushy. To make a cold...

Im Focus: Micro energy harvesters for the Internet of Things

Fraunhofer IWS Dresden scientists print electronic layers with polymer ink

Thin organic layers provide machines and equipment with new functions. They enable, for example, tiny energy recuperators. In future, these will be installed...

Im Focus: Dynamik einzelner Proteine

Neue Messmethode erlaubt es Forschenden, die Bewegung von Molekülen lange und genau zu verfolgen

Das Zusammenspiel aus Struktur und Dynamik bestimmt die Funktion von Proteinen, den molekularen Werkzeugen der Zelle. Durch Fortschritte in der...

Im Focus: Dynamics of individual proteins

New measurement method allows researchers to precisely follow the movement of individual molecules over long periods of time

The function of proteins – the molecular tools of the cell – is governed by the interplay of their structure and dynamics. Advances in electron microscopy have...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

5th International Conference on Cellular Materials (CellMAT), Scientific Programme online

02.10.2018 | Event News

Major Project: The New Silk Road

01.10.2018 | Event News

"Boston calling": TU Berlin and the Weizenbaum Institute organize a conference in USA

21.09.2018 | Event News

 
Latest News

LISA: Scientists introduce a new method of statistical inference in neuroimaging (fMRI)

16.10.2018 | Medical Engineering

Physics: Not everything is where it seems to be

15.10.2018 | Physics and Astronomy

Microfluidic molecular exchanger helps control therapeutic cell manufacturing

15.10.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>