Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Depletion and enrichment of chlorine in perovskites observed

10.07.2015

After performance breakthroughs in 2012, a new class of organic-inorganic absorber material for solar cells has raised worldwide attention.

These organometallic halide perovskites are low cost, easy to process, and have enormous potential for efficient solar energy conversion: power conversion efficiencies up to 20.1 % have already been reported. Pioneering work has been led by the group of Henry Snaith at the University of Oxford in the UK.


X-ray spectroscopies have shown a higher chlorine concentration near the perovskite/TiO2 interface than throughout the rest of the perovskite film.

Credit: D. Starr/HZB

Chlorine tends to disappear

Optimal performance for these devices has been achieved with methylammonium lead halide absorbers which use a mixture of chlorine and iodine. Despite typical chlorine-to-iodine concentration ratios of 0.66 in the initial precursor solution, the perovskite films contain little or no chlorine. Depending on the processing procedures, chlorine tends to be depleted, whereas the iodine atoms remain in the material. Nevertheless, the chlorine seems to benefit the efficiency of the absorber material, but it is still not understood how and why.

Analysing deeper layers

Now, a team of HZB scientists has analysed samples from the Snaith group and unveiled how chlorine is distributed in the perovskite absorber layer. They used X-ray spectroscopies at the BESSY-II facility to probe the distribution of chlorine in a mixed halide, organic-inorganic perovskite absorber layer.

With hard X-ray photoelectron spectroscopy (HAXPES) experiments at the KMC-1 beamline they probed the surface of perovskite layers and found nearly no chlorine near the surface. With a different method, fluorescence yield X-ray absorption spectroscopy (FY-XAS), they probed more deeply into the layers of the sample.

"We have observed a higher concentration of chlorine near the perovskite/TiO2 interface than in the rest of the thin film", David Starr, first author of the publication in Energy & Environmental Science explains.

Chlorine boosts efficiency

Chlorine may potentially play a role in mitigating the effects of vacancies, which favor recombination and charge carrier loss, or providing a better template on which to grow the perovskite film. "These results may help to understand the apparent beneficial effects of chlorine for perovskite solar cell device performance and could potentially provide a route to device optimization," Marcus Bär, who heads the HZB team, says.

"The ultimate goal is to use this knowledge to tailor deposition processes and material compositions to achieve specific desirable properties; perhaps by completely understanding the beneficial role of chlorine in the Pb-based perovskite material, we can overcome some of the difficulties involved in replacing the Pb with a less toxic material."

###

Publication: Energy Environ. Sci., 2015, 8, 1609, DOI: 10.1039/c5ee00403a
Direct observation of an inhomogeneous chlorine distribution in CH3NH3PbI3_xClx layers: surface depletion and interface enrichment. David E. Starr, Golnaz Sadoughi,
Evelyn Handick, Regan G. Wilks, Jan H. Alsmeier, Leonard Köhler, Mihaela Gorgoi, Henry J. Snaith and Marcus Bär

Media Contact

Antonia Roetger
antonia.roetger@helmholtz-berlin.de
49-308-062-43733

 @HZBde

http://www.helmholtz-berlin.de 

Antonia Roetger | EurekAlert!

More articles from Materials Sciences:

nachricht New gel-like coating beefs up the performance of lithium-sulfur batteries
22.03.2017 | Yale University

nachricht Pulverizing electronic waste is green, clean -- and cold
22.03.2017 | Rice University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short

23.03.2017 | Life Sciences

Researchers use light to remotely control curvature of plastics

23.03.2017 | Power and Electrical Engineering

Sea ice extent sinks to record lows at both poles

23.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>