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 Physics, photosynthesis and solar cells
01.12.2016 | University of California - Riverside

nachricht New process produces hydrogen at much lower temperature
01.12.2016 | Waseda 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: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

NASA's AIM observes early noctilucent ice clouds over Antarctica

05.12.2016 | Earth Sciences

Shape matters when light meets atom

05.12.2016 | Physics and Astronomy

Researchers uncover protein-based “cancer signature”

05.12.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>