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.
Dr. Daniel Niesner
Phone: +49 9131 8528403
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
Argonne and CERN weigh in on the origin of heavy elements
31.03.2020 | DOE/Argonne National Laboratory
Physicist from Hannover Develops New Photon Source for Tap-proof Communication
30.03.2020 | Leibniz Universität Hannover
An international team with the participation of Prof. Dr. Michael Kues from the Cluster of Excellence PhoenixD at Leibniz University Hannover has developed a new method for generating quantum-entangled photons in a spectral range of light that was previously inaccessible. The discovery can make the encryption of satellite-based communications much more secure in the future.
A 15-member research team from the UK, Germany and Japan has developed a new method for generating and detecting quantum-entangled photons at a wavelength of...
Together with their colleagues from the University of Würzburg, physicists from the group of Professor Alexander Szameit at the University of Rostock have devised a “funnel” for photons. Their discovery was recently published in the renowned journal Science and holds great promise for novel ultra-sensitive detectors as well as innovative applications in telecommunications and information processing.
The quantum-optical properties of light and its interaction with matter has fascinated the Rostock professor Alexander Szameit since College.
Researchers at the University of Zurich show that different stem cell populations are innervated in distinct ways. Innervation may therefore be crucial for proper tissue regeneration. They also demonstrate that cancer stem cells likewise establish contacts with nerves. Targeting tumour innervation could thus lead to new cancer therapies.
Stem cells can generate a variety of specific tissues and are increasingly used for clinical applications such as the replacement of bone or cartilage....
An international research team led by Kiel University develops an extremely porous material made of "white graphene" for new laser light applications
With a porosity of 99.99 %, it consists practically only of air, making it one of the lightest materials in the world: Aerobornitride is the name of the...
Researchers at Graz University of Technology have developed a framework by which wireless devices with different radio technologies will be able to communicate directly with each other.
Whether networked vehicles that warn of traffic jams in real time, household appliances that can be operated remotely, "wearables" that monitor physical...
26.03.2020 | Event News
23.03.2020 | Event News
03.03.2020 | Event News
31.03.2020 | Life Sciences
31.03.2020 | Life Sciences
31.03.2020 | Medical Engineering