Chemical fluctuations in polycrystalline thin-films for photovoltaic devices
Within this project we investigate chemical fluctuations at the nanometre scale in polycrystalline Cu(In,Ga)Se2 and CuInS2 thin-flims used as absorber material in solar cells.
Secondary phase formation as well as chemical fluctuations such as impurity segregation at structural defects like grain boundaries can significantly affect the optoelectronical properties of photovoltaic materials. Within this project we investigate such chemical fluctuations at the nanometre scale in polycrystalline Cu(In,Ga)Se2 and CuInS2 thin-flims used as absorber material in solar cells. We apply combined scanning transmission electron microscopy (STEM) with energy dispersive X-ray spectroscopy (EDX) as well as correlated transmission Kikuchi diffraction (TKD) and atom probe tomography (APT).
Accumulation and diffusion of Na (green) along Cu depleted structural defects (blue) in epitaxial grown CuInSe2 films on GaAs substrate
Mechanistic description of In/Ga interdiffusion. STEM-BF image of a cross section from a Na2Se treated CuInSe2 film grown on GaAs substrate and corresponding Ga, In and Cu elemental maps.
Mechanistic description of In/Ga interdiffusion. STEM-BF image of a cross section from a Na2Se treated CuInSe2 film grown on GaAs substrate and corresponding Ga, In and Cu elemental maps.
Image quality maps from a TKD measurement of an APT needle and corresponding unique color map showing a RHAGB (blue) and ∑3 TB (red). Na & C co-segregation as well as Cu enrichment (blue iso-concentration surface) at the RHAGB. Concentration profile across the RHAGB revealing an atomic redistribution.
Image quality maps from a TKD measurement of an APT needle and corresponding unique color map showing a RHAGB (blue) and ∑3 TB (red). Na & C co-segregation as well as Cu enrichment (blue iso-concentration surface) at the RHAGB. Concentration profile across the RHAGB revealing an atomic redistribution.
This project (B06) is part of the SFB 1394 collaborative research centre (CRC), focused on structural and atomic complexity, defect phases and how they are related to material properties. The project started in January 2020 and has three important work packages: (i) fracture analysis of intermetallic phases, (ii) the relationship of fracture to…
Grain boundaries (GBs) affect many macroscopic properties of materials. In the case of metals grain growth, Hall–Petch hardening, diffusion, and electrical conductivity, for example, are influenced or caused by GBs. The goal of this project is to investigate the different GB phases (also called complexions) that can occur in tilt boundaries of fcc…
In order to develop more efficient catalysts for energy conversion, the relationship between the surface composition of MXene-based electrode materials and its behavior has to be understood in operando. Our group will demonstrate how APT combined with scanning photoemission electron microscopy can advance the understanding of complex relationships…
This project studies the mechanical properties and microstructural evolution of a transformation-induced plasticity (TRIP)-assisted interstitial high-entropy alloy (iHEA) with a nominal composition of Fe49.5Mn30Co10Cr10C0.5 (at. %) at cryogenic temperature (77 K). We aim to understand the hardening behavior of the iHEA at 77 K, and hence guide the future design of advanced HEA for cryogenic applications.
Because of their excellent corrosion resistance, high wear resistance and comparable low density, Fe–Al-based alloys are an interesting alternative for replacing stainless steels and possibly even Ni-base superalloys. Recent progress in increasing strength at high temperatures has evoked interest by industries to evaluate possibilities to employ…
This project studies the influence of grain boundary chemistry on mechanical behaviour using state-of-the-art micromechanical testing systems. For this purpose, we use Cu-Ag as a model system and compare the mechanical response/deformation behaviour of pure Cu bicrystals to that of Ag segregated Cu bicrystals.
Nickel-based alloys are a particularly interesting class of materials due to their specific properties such as high-temperature strength, low-temperature ductility and toughness, oxidation resistance, hot-corrosion resistance, and weldability, becoming potential candidates for high-performance components that require corrosion resistance and good…
In this project, we aim at significantly enhancing the strength-ductility combination of quinary high-entropy alloys (HEAs) with five principal elements by simultaneously introducing interstitial C/N and the transformation induced plasticity (TRIP) effect. Thus, a new class of alloys, namely, interstitially alloyed TRIP-assisted quinary (five-component) HEAs is being developed.
Despite the immanent advantages of metals and alloys processed by additive manufacturing (e.g. design freedom for complex geometry) and unexpected merits (e.g. superior mechanical performance) of AM processes, there are several remaining issues that need to be addressed in order to practically apply AM alloys to various industries. One of the most important issues is the mechanical behavior of AM alloys under hydrogen environments, since it is easily encountered in the industrial fields and has generally detrimental effects on metals and alloys.
The goal of this project is to optimize the orientation mapping technique using four-dimensional scanning transmission electron microscopy (4D STEM) in conjunction with precession electron diffraction (PED). The development of complementary metal oxide semiconductor (CMOS)-based cameras has revolutionized the capabilities in data acquisition due to…
