Technical University of Berlin

About: Technical University of Berlin is a education organization based out in Berlin, Germany. It is known for research contribution in the topics: Quantum dot & Laser. The organization has 27292 authors who have published 59342 publications receiving 1414623 citations. The organization is also known as: Technische Universität Berlin & TU Berlin.

The need for a pressure-term representation in empirical Galerkin models of incompressible shear flows

Abstract: Low-dimensional empirical Galerkin models are developed for spatially evolving laminar and transitional shear layers, based on a Karhunen–Loeve decomposition of incompressible two- and three-dimensional Navier–Stokes simulations. It is shown that the key to an accurate Galerkin model is a novel analytical pressure-term representation. The effect of the pressure term is elucidated by a modal energy-flow analysis in a mixing layer, which generalizes the framework developed by Rempfer (1991). In convectively unstable shear layers, it is shown in particular that neglecting small energy terms leads to large amplitude errors in the Galerkin model. The effect of the pressure term and small neglected energy flows is very important for a two-dimensional mixing layer, is less pronounced for the three-dimensional analogue, and can be considered as small in an absolutely unstable wake flow.

Electrochemical Catalyst–Support Effects and Their Stabilizing Role for IrOx Nanoparticle Catalysts during the Oxygen Evolution Reaction

Abstract: Redox-active support materials can help reduce the noble-metal loading of a solid chemical catalyst while offering electronic catalyst–support interactions beneficial for catalyst durability. This is well known in heterogeneous gas-phase catalysis but much less discussed for electrocatalysis at electrified liquid–solid interfaces. Here, we demonstrate experimental evidence for electronic catalyst–support interactions in electrochemical environments and study their role and contribution to the corrosion stability of catalyst/support couples. Electrochemically oxidized Ir oxide nanoparticles, supported on high surface area carbons and oxides, were selected as model catalyst/support systems for the electrocatalytic oxygen evolution reaction (OER). First, the electronic, chemical, and structural state of the catalyst/support couple was compared using XANES, EXAFS, TEM, and depth-resolved XPS. While carbon-supported oxidized Ir particle showed exclusively the redox state (+4), the Ir/IrOx/ATO system exhibited ...

Conformal monolayer contacts with lossless interfaces for perovskite single junction and monolithic tandem solar cells

Abstract: The rapid rise of perovskite solar cells (PSCs) is increasingly limited by the available charge-selective contacts. This work introduces two new hole-selective contacts for p–i–n PSCs that outperform all typical p-contacts in versatility, scalability and PSC power-conversion efficiency (PCE). The molecules are based on carbazole bodies with phosphonic acid anchoring groups and can form self-assembled monolayers (SAMs) on various oxides. Besides minimal material consumption and parasitic absorption, the self-assembly process enables conformal coverage of arbitrarily formed oxide surfaces with simple process control. The SAMs are designed to create an energetically aligned interface to the perovskite absorber without non-radiative losses. For three different perovskite compositions, one of which is prepared by co-evaporation, we show dopant-, additive- and interlayer-free PSCs with stabilized PCEs of up to 21.1%. Further, the conformal coverage allows to realize a monolithic CIGSe/perovskite tandem solar cell with as-deposited, rough CIGSe surface and certified efficiency of 23.26% on an active area of 1 cm2. The simplicity and diverse substrate compatibility of the SAMs might help to further progress perovskite photovoltaics towards a low-cost, widely adopted solar technology.

Opening up for competitive advantage – How Deutsche Telekom creates an open innovation ecosystem

Abstract: When, on 21st September 2006, ‘The Economist’ compared incumbent telecommunication operators with dinosaurs that could soon face extinction, most readers were ready to agree. The mixture of declining revenues and fierce competition was believed to shake the market and soon to dethrone former national champions. However, there are ways to fight that extinction and one way is to open up for competitive advantage. This paper reflects on a case study at Deutsche Telekom, the German national telecommunication operator. The aim of this study is to analyse to what extent the open innovation paradigm has been embraced inside this now multinational company. Using empirical evidence from 15 in-depth interviews, we identify 11 open innovation instruments and detail their value contribution. We can show that Deutsche Telekom has successfully enhanced its innovation capacity by opening up its traditional development process and embracing external creativity and knowledge resources.