Das Seminar findet üblicherweise Donnerstags am
Wilhelm-Conrad-Röntgen Campus, Dep. Si Photovoltaik EE-IS im
Seminarraum 227, 12489 Berlin, Kekuléstr.5, im 1. OG. statt.
Beginn: 10:15 Uhr
(ab10:00 Uhr Kaffee und Kekse).
15:00 – 16:30
Hörsaal BESSY II
Chair: Dr. Burkhard Beckhoff (PTB)
Dr. Sascha Nowak
“Analysis of Lithium Ion Batteries – Demands, State-of-the-art and Challenges”
Being successfully introduced into the market only 25 years ago, lithium ion batteries are already state-of-the-art power sources for portable electronic devices and the most promising candidate for energy storage in large-size batteries. A major challenge is the degradation of the cell constituents, which is called aging and which minimizes both storage lifetime (calendar life) and operation lifetime (cycle life). Since the complexity of the lithium ion battery with regard to composition as well as reaction, degradation and aging is challenging and demands the combination of several techniques, this interdisciplinary research field is still at the beginning with respect to understanding all the reaction degradation and aging mechanisms. However, it is clear already today, that the continuous improvement and adaptation of advanced analysis methods will be the key for the accurate chemical analysis of batteries and its components, thus unravelling the unanswered degradation mechanisms and those to come.
Qin Tan will speak about
“Temperature dependent diffusion of residual solvent molecules during CH3NH3PbI3 layer formation and impact on solar cells”
Hybrid organic-inorganic metal halide perovskites are usually prepared from solutions. A solution contains precursor salts and solvents such as DMSO and DMF. During the formation of a crystalline perovskite layer, solvent molecules diffuse out. Residual solvent molecules can remain in the crystal lattice and can influence the performance of solar cells. For the analysis of the influence of residual solvent molecules on the performance of solar cells, the amount of residual molecules in perovskite layers shall be measured. In our approach, we focus on the CH3NH3PbI3 system which has the lowest complexity. For formation of the intermediate phase and for defining practically ideal boundary conditions for out-diffusion, a vacuum-assisted treatment was applied. The temperature dependent out-diffusion of DMSO from CH3NH3PbI3 precursor layers was investigated by measuring the S/Pb molar ratio in by high-resolution continuum source absorption spectroscopy (HR-CSAS) and the evolution of the S=O vibrational mode with infrared spectroscopic ellipsometry (IRSE). The diffusion coefficients were extracted by applying a diffusion model in a homogeneous layer. The diffusion coefficient of DMSO in CH3NH3PbI3 amounted to about 10-11 cm²/s at 100°C. The diffusion coefficient was activated by two processes with activation energies of 0.6 and 1.8 eV which can be explained by decomposition of DMSO complexes and by activation of DMSO trapped in the perovskite lattice. The S/Pb molar ratio had, for example, strong influence on the fill factor of solar cells. Furthermore, it seems that some residual DMSO is useful for the preparation of homogeneous CH3NH3PbI3 layers and to passivate defect states in the material. In future, it will be very interesting to apply our approach to complex systems with more cations, different preparation conditions, various layer architectures etc.
22.05.2019 (Wednesday !)
Location: seminar room of EE-IS (Kekulé Str. 5, 12489 Berlin)
Prof. Warren Jackson
Electronic Materials and Devices Lab
“Brief survey of Geometric Algebra and its Application to Physics and Engineering”
Many of the mathematical forms used in physics, engineering, robotics, and computer vision such as complex numbers, matrices, vector calculus, quaternions, spinors etc are actually part of a unified mathematics known as geometric algebra. While it was discovered in 1873 by William Clifford, only recently has geometric algebra been used in main stream science and technology. Geometric algebra provides a concise description of nature including relativity, quantum mechanics, electromagnetism, and classical mechanics in a coordinate free geometrical language and provides new insight into many of these fields. In this talk, I will attempt to introduce the ideas of geometric algebra, how it generalizes and unifies the usual mathematics, and discuss its application to various aspects of physics and engineering. I hope to convey a hint of some of the new insights which arise from using geometric algebra descriptions.