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.
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
Antonia Roetger | EurekAlert!
New design improves performance of flexible wearable electronics
23.06.2017 | North Carolina State University
Plant inspiration could lead to flexible electronics
22.06.2017 | American Chemical Society
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
26.06.2017 | Life Sciences
26.06.2017 | Physics and Astronomy
26.06.2017 | Information Technology