03 Fakultät Chemie

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Author: search.filters.author.Clemens, OliverSubject: search.filters.subject.660

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    The Fermi energy as common parameter to describe charge compensation mechanisms : a path to Fermi level engineering of oxide electroceramics
    (2023) Klein, Andreas; Albe, Karsten; Bein, Nicole; Clemens, Oliver; Creutz, Kim Alexander; Erhart, Paul; Frericks, Markus; Ghorbani, Elaheh; Hofmann, Jan Philipp; Huang, Binxiang; Kaiser, Bernhard; Kolb, Ute; Koruza, Jurij; Kübel, Christian; Lohaus, Katharina N. S.; Rödel, Jürgen; Rohrer, Jochen; Rheinheimer, Wolfgang; De Souza, Roger A.; Streibel, Verena; Weidenkaff, Anke; Widenmeyer, Marc; Xu, Bai-Xiang; Zhang, Hongbin
    Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering.
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    One‐step thermal gradient‐ and antisolvent‐free crystallization of all‐inorganic perovskites for highly efficient and thermally stable solar cells
    (2022) Byranvand, Mahdi Malekshahi; Kodalle, Tim; Zuo, Weiwei; Magorian Friedlmeier, Theresa; Abdelsamie, Maged; Hong, Kootak; Zia, Waqas; Perween, Shama; Clemens, Oliver; Sutter‐Fella, Carolin M.; Saliba, Michael
    All‐inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their heat‐sensitive hybrid organic–inorganic counterparts. In particular, CsPbI2Br shows the highest potential for developing thermally‐stable perovskite solar cells (PSCs) among all‐inorganic compositions. However, controlling the crystallinity and morphology of all‐inorganic compositions is a significant challenge. Here, a simple, thermal gradient‐ and antisolvent‐free method is reported to control the crystallization of CsPbI2Br films. Optical in situ characterization is used to investigate the dynamic film formation during spin‐coating and annealing to understand and optimize the evolving film properties. This leads to high‐quality perovskite films with micrometer‐scale grain sizes with a noteworthy performance of 17% (≈16% stabilized), fill factor (FF) of 80.5%, and open‐circuit voltage (VOC) of 1.27 V. Moreover, excellent phase and thermal stability are demonstrated even after extreme thermal stressing at 300 °C.
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    PEO infiltration of porous garnet-type lithium-conducting solid electrolyte thin films
    (2021) Waidha, Aamir Iqbal; Vanita, Vanita; Clemens, Oliver
    Composite electrolytes containing lithium ion conducting polymer matrix and ceramic filler are promising solid-state electrolytes for all solid-state lithium ion batteries due to their wide electrochemical stability window, high lithium ion conductivity and low electrode/electrolyte interfacial resistance. In this study, we report on the polymer infiltration of porous thin films of aluminum-doped cubic garnet fabricated via a combination of nebulized spray pyrolysis and spin coating with subsequent post annealing at 1173 K. This method offers a simple and easy route for the fabrication of a three-dimensional porous garnet network with a thickness in the range of 50 to 100 µm, which could be used as the ceramic backbone providing a continuous pathway for lithium ion transport in composite electrolytes. The porous microstructure of the fabricated thin films is confirmed via scanning electron microscopy. Ionic conductivity of the pristine films is determined via electrochemical impedance spectroscopy. We show that annealing times have a significant impact on the ionic conductivity of the films. The subsequent polymer infiltration of the porous garnet films shows a maximum ionic conductivity of 5.3 × 10-7 S cm-1 at 298 K, which is six orders of magnitude higher than the pristine porous garnet film.