Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Uncovering the Secrets of Super Solar Power Perovskites

18.03.2015

University of Utah study of magnetic field effects could help researchers to fully optimize organic-inorganic hybrid perovskite solar cells

The best hope for cheap, super-efficient solar power is a remarkable family of crystalline materials called hybrid perovskites. In just five years of development, hybrid perovskite solar cells have attained power conversion efficiencies that took decades to achieve with the top-performing conventional materials used to generate electricity from sunlight.


University of Utah

Schematic presentation of the obtained magnetic field effect of photocarriers in photovoltaic cells and injected carriers in light emitting diodes based on hybrid organic/inorganic perovskite semiconductors, which originates from different precession frequencies of the electron (red) and hole (blue) about an applied magnetic field (arrow).

Now researchers at the University of Utah, in collaboration with the University of Texas at Dallas, have uncovered some of the secrets behind the amazing material’s performance. The findings, published today in the journal Nature Physics, help fill a deep void in hybrid perovskite solar cell research. Scientists and engineers have lacked a clear understanding of the precise goings on at the molecular level.

Among the practical results of the new study is proof of a way to rapidly test the performance of different prototypes of hybrid perovskite materials using magnetic fields, according to lead author Charlie Zhang, a post-doctoral research fellow, and senior author Z. Valy Vardeny, a distinguished professor of physics at the University of Utah.

“Our group has unique expertise in magnetic field effects,” Vardeny says. “We wanted to see if magnetic field effects would tell us why the efficiency is so high.”

Probing electronic properties
Applying a magnetic field makes it possible to glean clues about the behavior of electrons and “holes” in semiconductor compounds. In photovoltaic solar cells, molecules absorb incoming photons of sunlight. Each absorbed photon can generate an exciton, the pairing of an electron and a corresponding electron hole. These pairings are short-lived and split into free, charge-carrying particles that drive an electric current.

Electrons and holes have a magnetic-related property called ‘spin’, a form of angular momentum; and the torque of a magnetic field can alter the spin direction. Spin can’t be observed directly, but spin properties can be inferred by looking at readily measurable properties, such as changes in the electrical conductivity of a material, or changes in photoluminescence – its tendency to emit light after absorbing photons – when it is subjected to a magnetic field.

Zhang and colleagues measured magnetic field-induced changes in these properties in an assortment of fabricated hybrid perovskite solar cells having different solar power conversion efficiencies. They used a typical hybrid perovskite material, methylammonium lead iodide, or MAPbI3. (Hybrid perovskites follow the naming convention MAPbX3, with MA denoting the organic methylammonium group that is combined with an inorganic group made of lead (Pb) and either chloride, bromide, or iodide (X)). Contrary to conventional wisdom in the field, the Utah scientists found pronounced magnetic field effects. The magnetic properties of the heavy atoms of lead and iodine were thought to minimize magnetic field effects in hybrid perovskite solar cells.

How it works
The researchers proposed a mechanism to explain the effects based on how a magnetic field changes the spin configuration of electron-hole pairs. The spin configuration affects the rate at which electron-hole pairs split apart or recombine, which in turn respectively changes the electrical conductivity and photoluminescence of the perovskite. They dubbed this effect the ‘delta-g mechanism’, with g being a factor that describes the magnetic moment of an electron in the material. Delta-g is the difference between the g-factors of an electron and hole, a difference that becomes crucial in how hybrid perovskite materials perform.

They verified this mechanism by measuring delta-g directly using a technique called field-induced circular polarized emission. It proved to be much larger than delta-g in ordinary organic solar cells, as would be expected if the delta-g mechanism were correct. For further confirmation, the researchers used a spectroscopy technique to measure the fleeting lifetimes – in trillionths of a second – of electron-hole pairs created by light absorption in the hybrid perovskite solar cells. The results also fit the delta-g mechanism.

Answering key questions
The findings point to an answer to a critical question: whether hybrid perovskite devices behave more like silicon solar cells or like so-called excitonic solar cells made of organic polymers. Vardeny said the magnetic field effects nailed down by his group are telling. “This material is not excitonic. If it were, we would not see this effect. It is not like organic photovoltaic materials.”

The efficiency of converting sunlight to electric power has a theoretical limit of 33 percent. The hybrid perovskite photovoltaic devices are pushing 20 percent, not as good as the 26 percent of the best silicon cells, but closing in – and the hybrid perovskites can be produced at a fraction of the cost. The new findings provide more detailed understanding of the underlying physics that should help researchers to fully optimize hybrid perovskite solar cells.

Harnessing solar energy using photovoltaic cells has become more accessible with the addition of the hybrid perovskite 'miracle materials', Vardeny says. "This is important since the gasoline price at the pumps would not stay that low forever."

University of Utah Communications
75 Fort Douglas Boulevard, Salt Lake City, UT 84113
801-581-6773 fax: 801-585-3350
www.unews.utah.edu

Contact Information
-- Z. Valy Vardeny, distinguished professor of physics – office (801) 581-8372, cell 801-278-5433, val@physics.utah.edu
-- Charlie Zhang, title – office 801-585-1653, cell 801-739-2098, chzhang@physics.utah.edu
-- Joe Rojas-Burke, senior science writer, University of Utah Communications Office –
office 801-585-6861, cell 503-896-1079, joe.rojas@utah.edu

Joe Rojas-Burke | newswise

More articles from Power and Electrical Engineering:

nachricht A big nano boost for solar cells
18.01.2017 | Kyoto University and Osaka Gas effort doubles current efficiencies

nachricht Multiregional brain on a chip
16.01.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>