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IWCE19 - Poster award for Javier Villalobos

Javier Villalobos has been awarded for the best poster at the International Workshop on Correlated Dynamics in Energy Conversion (IWCE 19) in Göttingen. The doctoral student works in the young investigator group "Oxygen Evolution Mechanism Engineering". His research contributes to a better understanding of electrocatalytic oxygen evolution.

On his poster, Javier Villalobos presented first results on the electrochemical synthesis of spinel oxides, which can be used as catalysts for the oxygen evolution reaction. The title of his poster is "Fabrication of defined spinel oxides containing manganese and cobalt by electrodeposition as model electrodes for the oxygen evolution reaction".

The presented results are the first step towards developing a model system for systematic studies on such catalysts. It is crucial to deposit films with controlled composition and microstructure. These materials will soon be investigated using operando methods on BESSY II to better understand the known differences in activity.

"With his poster, Javier Villalobos laid the foundation for a better understanding of the oxygen evolution reaction in order to produce sustainable fuels based on water (e.g. hydrogen) more cheaply," explains Dr. Marcel Risch, supervisor of the project. Since March 2019, he has been setting up a young investigator group at HZB with a Starting Grant from the European Research Council (ERC).

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MRS Spring Meeting 2019 - Poster award for Jakob Bombsch

At the spring meeting of the Materials Research Society, Jakob Bombsch received an award for his poster on CIGSe absorbers for thin-film photovoltaics. Bombsch is a researcher in the department for Interface Design headed by Prof. Marcus Bär. 

In his doctoral thesis, Jakob Bombsch mainly investigates compound semiconductors made of copper, gallium, indium and selenide (CIGSe), which can be used as absorber material in thin-film photovoltaics. Recent increases in efficiency have been achieved by so-called "post-deposition treatments" of the CIGSe layers with alkali fluorides.

On his poster, Jakob Bombsch presented results on the influence of such post-deposition treatments on the chemical and electronic surface structure of CIGSe absorbers. He analyzed how these changes could be related to the observed increase in efficiency. The investigations were performed with photoelectron spectroscopy in the SISSY laboratory at EMIL, at the HiKE terminal station at BESSY II and the BL15XU beamline at SPring-8 in Japan.

The spring meeting of the Materials Research Society took place from April 22 - 26, 2019 in Phoenix, USA.

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E-MRS 2018: Prizes for two doctoral researchers

At the spring meeting of the European Materials Research Society from 18-22 June 2018 in Strasbourg, Hannes Hempel received the prize for the best talk and Sara Niedenzu was awarded for her poster. Both are PhD students at the MatSEC graduate school at HZB. The E-MRS spring conference is the largest materials research conference in Europe with 2,500 participants.

With his talk, Hannes Hempel applied for the prize of the symposium on thin-film chalcogenides in photovoltaics, which was attended by about 350 experts. The physicist, who is working on his doctorate in Thomas Unold's team, explained the influence of "bandtails" on the transport properties and recombination of charge carriers in polycrystalline kesterites. "I was one of four finalists in the final selection, where we were able to present our career, our role in the team and once again the main results. After all, me and another researcher won," explains Hempel, who is not only pleased about the recognition but also about the prize money of 450 €. In the future he will set up the new laboratory of Thomas Unold for terahertz spectroscopy, in which ultra-fast dynamics of the crystal lattice can be characterized in addition to mobility and lifetime of charge carriers.

Sara Niedenzu presented the crystal structures of chalcogenide semiconductors with larger band gaps on her poster. It deals with the synthesis of polycrystalline powders of different mixing series and the structural characterization of these materials, which are used as materials for energy conversion in photovoltaics. Sara Niedenzu has just finished her first year in the team of Prof. Susan Schorr, who congratulates her: "It's great to receive an award at this early stage of the doctorate at an international conference", Susan Schorr says.

Title of talk given by Hannes Hempel: “Charge Carrier Dynamics in Tail States of polycrystalline Cu2ZnSnSe4“.

Publication on the topic:  “Intragrain charge transport in kesterite thin films - Limits arising from carrier localization“

Poster by Sara Niedenzu: “Structural characterization of wide bandgap Cu‐Zn‐IV‐chalcogenide based semiconductors”

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Poster award for Monika Raja Thulasimani

Monika Raja Thulasimani is working on hybrid thermoelectrics at the Graduate School MatSec at HZB. During the European Conference on Thermoelectrics 2017 her poster contribution was selected for an award. The young scientist described a solution based synthesis in order to design more efficient thermoelectric materials.

“These materials can be produced by a simple aqueous synthesis that is inexpensive for mass production; in our case, we use a template-based approach, whereby hybrid composites consisting of nanostructured Te in a PEDOT:PSS matrix are used to form Ag2Te/PEDOT:PSS hybrid materials”, said Monika Raja Thulasimani. She used GI-XRD and TEM to characterize the morphology of different samples. Then, she compared the morphological results to the thermoelectric properties in order to gain insight into the structure-property relationships of these materials.

Thermoelectric materials exhibit the thermoelectric effect where thermal energy is directly converted into electrical potential resulting in motion of the charge carriers. Thermoelectrics have traditionally been used in applications such as automotive waste heat recovery, but emerging applications related to consumer electronics, optical materials, and local cooling in computers have been proposed, and we are interested in hybrid thermoelectric materials towards this end.

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First doctoral candidates of MatSEC completed their doctorate

The first students of the graduate school MatSEC (Materials for Solar Energy Conversion) have defended successfully their PhD thesis. The graduate school, which is organised jointly by Dahlem Research School of Freie Universität Berlin, is now open for new PhD-students. The research portfolio, which was focused on kesterites, does now include wide bandgap semiconductors and thermoelectrica as well.

MatSEC was the first graduate school, HZB had installed under the roof of Dahlem Research School and in cooperation with several universities in the region. „The graduate school MatSEC is to be continued, but with a much broader research field“, Prof. Dr. Susan Schorr, speaker of MatSEC explains. The organisators can rely on their cooperation with other research institutes and universities in Germany and have won international partners: the Weizmann-Institute of Science in Rehovot and the Hebrew University in Jerusalem. Young scientists can apply for PhD grants in MatSEC now. 

In the summer term 2013 as well as the winter term 2013/2014 the first seven PhD students of the newly established graduate school MatSEC had started their PhD at the HZB. In December 2016 the first four students have finished: Anna Ritscher at the Technical University Berlin, Marcel Quennet and Laura Elisa Valle Rios as well as Kai Neldner at Freie Universität Berlin.

The young scientists focused their work on structure-function relations in kesterites, a quaternary compound semiconductor which can be used as absorber material in thin film solar cells. While Marcel Quennet dealed with first principle calculations, Anna Ritscher, Laura Elisa Valle Rios and Kai Neldner worked experimentally using also the instrumentation at HZB's two large scale facilities. All have already published their results in a number of papers. Further degrees are expected in spring: Leonard Köhler has already submitted his PhD thesis at the BTU Cottbus-Senftenberg, Anastasia Irkhina and Martin Handwerk are close to its completion.

Doctoral Studies at the HZB within Graduate Schools

The HZB currently offers graduate studies in four graduate schools in cooperation with universities in the region. The range of subject areas for the graduate schools focusses on researching various materials for the energy conversion. Graduates studies are fundamentally available for all of the research fields in which the HZB conducts research.

With the successive establishment of graduate schools, the HZB is implementing one of the main requirements of the Doctoral Studies Guidelines of the Helmholtz Association. In future, all of the doctoral studies at the HZB shall be based around organised graduate schools in conjunction with universities.

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ECM29 Poster prize for Laura Elisa Valle Rios

The poster contribution of Laura Elisa Valle Rios (HZB-Department Crystallography) was awarded the CrystEngComm poster price of the Royal Society of Chemistry at the 29th European Crystallographic Meeting (ECM29) in Rovinj (Croatia). Laura Elisa, a PhD student in the Marie-Curie Initial Training network KESTCELLS and the HZB Graduate School "Materials for Solar Energy Conversion" (MatSEC).

She presented results on structural properties of Kesterites (Cu2ZnSnSe4 - CZTSe) in relation to its stoichiometry deviations.

The best performances of Kesterite-based thin film solar cells with converion efficiencies of 12.6% were obtained with an absorber material quite different from the stoichiometric compound Cu2ZnSn(S,Se)4, especially with a Cu-poor/Zn-rich composition. Because the electronic properties of a semiconductor are strongly related to its crystal structure, it is of great interest to study the nature of stoichiometry deviations systematically and to connect issues such as phase existence limits.

Laura Elisa Valle Rios synthesized off-stoichiometric CZTSe powder samples by solid state reaction and studied the structural and chemical properties. Here she applied different analytical methods using also the HZB's large scale facilities BESSY II and BER II. Moreover she performed experiments at the Spallation Neutron Source (SNS) in Oakridge (US). With the results she obtained from complementary neutron and synchrotron X-ray diffraction experiments  she was able to prove  that CZTS can accomodate deviations from stoichiometry without collapse of the kesterite type structure by the formation of certain point defects. Laura Elisa could show correlations between chemical composition of the kesterite type semiconductor and intrinsic point defects and defect concentrations. Thus the crystal structure of CZTS can self-adapt to Cu-poor/Zn-rich and Cu-rich/Zn-poor compositions without any structural changes except in terms of the cation distribution.

Laura Elisa Valle Rios works at the HZB (EM-AKR) as a PhD student in the EU-funded Marie-Curie Initial Training Network KESTCELLS (Training for sustainable low cost PV technologies: development of kesterite based efficient solar cells). She is enrolled at the Freie Universtaet Berlin in the joint graduate school "Materials for Solar Energy Conversion" (MatSEC).

Susan Schorr

MRS Spring Meeting 2015 - Poster award for Kai Neldner

The poster contribution of Kai Neldner (HZB-Department Crystallography) was awarded a poster price of the Symposium "Thin-Film Compound Semiconductors" at the MRS Spring Meeting in San Francisco. Kai Neldner, a PhD student in the HZB Graduate School "Materials for Solar Energy Conversion" (MatSEC) has presented results on structural properties of Kesterites (Cu2ZnSnS4 - CZTS) in relation to its stoichiometry deviations.

The best performances of Kesterite-based thin film solar cells with converion efficiencies of 12.6% were obtained with an absorber material quite different from the stoichiometric compound Cu2ZnSn(S,Se)4, especially with a Cu-poor/Zn-rich composition. Because the electronic properties of a semiconductor are strongly related to its crystal structure, it is of great interest to study the nature of stoichiometry deviations systematically and to connect issues such as phase existence limits.

Kai Neldner synthesized off-stoichiometric CZTS powder samples by solid state reaction and studied the structural and chemical properties. He applied different analytical methods using also the HZB's large scale facilities BESSY II and BER II. With his obtained results he was able to prove  that CZTS can accomodate deviations from stoichiometry without collapse of the kesterite type structure by the formation of certain point defects. Thus the crystal structure of CZTS can self-adapt to Cu-poor/Zn-rich and Cu-rich/Zn-poor compositions without any structural changes except in terms of the cation distribution.

Susan Schorr

MatSEC research colloquium June 2015

Am 24. Juni trafen sich die Mitglieder der Graduiertenschule MatSEC zum halbjährlichen Forschungskolloquium auf dem Lise-Meitner-Campus. MatSEC wurde im Frühjahr 2013 unter dem Dach der Dahlem Research School der Freien Universität Berlin gegründet. Die Graduiertenschule bietet ein strukturiertes dreijähriges Promotionsprogramm und beschäftigt sich mit Kesterit-Verbindungshalbleiter.

Innerhalb dieses Themas war das Spektrum der Vorträge weit gefächert. Es reichte von der Synthese stöchiometrischer und nicht-stöchiometrischer Kesterite über die Charakterisierung  dieser Verbindungen bis hin zur Simulation und Berechnung der elektronischen Struktur. Ebenso standen Kesterite als Absorbermaterial in Dünnschichtsolarzellen im Fokus.

Die Promovierenden, die gleich beim Start der Graduiertenschule MatSEC ihre Arbeit begonnen haben, haben nun „Halbzeit“: Sie haben die Hälfte der für ihre Promotion zur Verfügung stehenden Zeit für ihr Projekt gearbeitet. Das Forschungskolloquium war deshalb ein guter Zeitpunkt, um über das bisher Erreichte zu diskutieren und die nächsten Schritte, schon im Hinblick auf das nicht mehr allzu weit entfernte Ende der Promotionszeit, zu planen.

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MatSEC official start

Well-structured Ph.D. program

New HZB Graduate School: Ph.D. candidates to study materials for energy conversion

Yesterday’s workshop was the official starting signal for the opening of the Helmholtz Center Berlin’s new Materials for Solar Energy Conversion (MatSEC) Graduate School. MatSEC is the first HZB graduate training program for the Center’s doctoral students. The school is located at the Dahlem Research School (DRS) of the Freie Universität Berlin (FU Berlin). Up to ten Ph.D. students will be able to take advantage of MatSEC’s course offerings while working towards their degree.

The MatSEC graduate school’s focus is on the study of kesterites, a new class of materials used in photovoltaics. Kesterites are considered highly promising absorption film candidates for thin-film photovoltaics and could potentially double as photoelectrodes for splitting water using solar energy. The ultimate goal is to arrive at a comprehensive understanding of the relationship between this connecting semiconductor’s internal structure and its properties. This knowledge could aid researchers in developing customized materials for use in more cost-effective and efficient solar cells.

Prof. Dr. Susan Schorr, head of the Department for Crystallography at the HZB and a professor at FU Berlin, is the new graduate school’s spokesperson.  Research groups at FU Berlin, the Technical University of Berlin, the Humboldt University of Berlin, and the Brandenburg University of Technology in Cottbus are all partners of the new graduate school. “It is precisely in this interdisciplinary research structure that MatSEC’s strengths lie,” says Schorr.

Doctoral students attend lectures that are relevant to their research at the different participating university campuses. Workshops, study abroad programs, and course offerings at the Dahlem Research School complement the program. “We’re thrilled that we’re able to offer seven additional spots for students as part of our graduate program,” says Gabriele Lampert, Ph.D. coordinator at the HZB.

HS