05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Surface charge density and induced currents by self-charging sliding drops(2024) Bista, Pravash; Ratschow, Aaron D.; Stetten, Amy Z.; Butt, Hans-Jürgen; Weber, Stefan A. L.Spontaneous charge separation in drops sliding over a hydrophobized insulator surface is a well-known phenomenon and lots of efforts have been made to utilize this effect for energy harvesting. For maximizing the efficiency of such devices, a comprehensive understanding of the dewetted surface charge would be required to quantitatively predict the electric current signals, in particular for drop sequences. Here, we use a method based on mirror charge detection to locally measure the surface charge density after drops move over a hydrophobic surface. For this purpose, we position a metal electrode beneath the hydrophobic substrate to measure the capacitive current induced by the moving drop. Furthermore, we investigate drop-induced charging on different dielectric surfaces together with the surface neutralization processes. The surface neutralizes over a characteristic time, which is influenced by the substrate and the surrounding environment. We present an analytical model that describes the slide electrification using measurable parameters such as the surface charge density and its neutralization time. Understanding the model parameters and refining them will enable a targeted optimization of the efficiency in solid–liquid charge separation.Item Open Access A high frequency alternating current heater using the advantages of a damped oscillation circuit for low voltage Li-ion batteries(2024) Oehl, Joachim; Gleiter, Andreas; Manka, Daniel; Fill, Alexander; Birke, Kai PeterIn many cases, batteries used in light e-mobility vehicles such as e-bikes and e-scooters do not have an active thermal management system. This poses a challenge when these batteries are stored in sub-zero temperatures and need to be charged. In such cases, it becomes necessary to move the batteries to a warmer location and allow them to acclimatize before charging. However, this is not always feasible, especially for batteries installed permanently in vehicles. In this work, we present an internal high-frequency AC heater for a 48 V battery, which is used for light electric vehicles of EU vehicle classes L1e and L3e-A1 for a power supply of up to 11 kW. We have taken advantage of the features of a damped oscillating circuit to improve the performance of the heater. Additionally, only a small inductor was added to the main current path through a cable with three windings. Furthermore, as the power electronics of the heater is part of the battery main switch, fewer additional parts inside the battery are required and therefore a cost and space reduction compared to other heaters is possible. For the chosen setup we reached a heating rate of up to 2.13 K min -1 and it was possible to raise the battery temperature from -10 °C to 10 °C using only 3.1% of its own usable capacity.Item Open Access All-perovskite tandem solar cells : from fundamentals to technological progress(2024) Lim, Jaekeun; Park, Nam-Gyu; Seok, Sang Il; Saliba, MichaelOrganic-inorganic perovskite materials have gradually progressed from single-junction solar cells to tandem (double) or even multi-junction (triple-junction) solar cells as all-perovskite tandem solar cells (APTSCs). Perovskites have numerous advantages: (1) tunable optical bandgaps, (2) low-cost, e.g. via solution-processing, inexpensive precursors, and compatibility with many thin-film processing technologies, (3) scalability and lightweight, and (4) eco-friendliness related to low CO2 emission. However, APTSCs face challenges regarding stability caused by Sn2+ oxidation in narrow bandgap perovskites, low performance due to Voc deficit in the wide bandgap range, non-standardisation of charge recombination layers, and challenging thin-film deposition as each layer must be nearly perfectly homogenous. Here, we discuss the fundamentals of APTSCs and technological progress in constructing each layer of the all-perovskite stacks. Furthermore, the theoretical power conversion efficiency (PCE) limitation of APTSCs is discussed using simulations.Item Open Access Three-step process for efficient solar cells with boron-doped passivated contacts(2024) Sharbaf Kalaghichi, Saman; Hoß, Jan; Linke, Jonathan; Lange, Stefan; Werner, Jürgen H.Crystalline silicon (c-Si) solar cells with passivation stacks consisting of a polycrystalline silicon (poly-Si) layer and a thin interfacial silicon dioxide (SiO2) layer show high conversion efficiencies. Since the poly-Si layer in this structure acts as a carrier transport layer, high doping of the poly-Si layer is crucial for high conductivity and the efficient transport of charge carriers from the bulk to a metal contact. In this respect, conventional furnace-based high-temperature doping methods are limited by the solid solubility of the dopants in silicon. This limitation particularly affects p-type doping using boron. Previously, we showed that laser activation overcomes this limitation by melting the poly-Si layer, resulting in an active concentration beyond the solubility limit after crystallization. High electrically active boron concentrations ensure low contact resistivity at the (contact) metal/semiconductor interface and allow for the maskless patterning of the poly-Si layer by providing an etch-stop layer in an alkaline solution. However, the high doping concentration degrades during long high-temperature annealing steps. Here, we performed a test of the stability of such a high doping concentration under thermal stress. The active boron concentration shows only a minor reduction during SiNx:H deposition at a moderate temperature and a fast-firing step at a high temperature and with a short exposure time. However, for an annealing time 𝑡anneal = 30 min and an annealing temperature 600 °C ≤ 𝑇anneal ≤ 1000 °C, the high conductivity is significantly reduced, whereas a high passivation quality requires annealing in this range. We resolve this dilemma by introducing a second, healing laser reactivation step, which re-establishes the original high conductivity of the boron-doped poly-Si and does not degrade the passivation. After a thermal annealing temperature 𝑇anneal = 985 °C, the reactivated layers show high sheet conductance (Gsh) with Gsh = 24 mS sq and high passivation quality, with the implied open-circuit voltage (iVOC) reaching iVOC = 715 mV. Therefore, our novel three-step process consisting of laser activation, thermal annealing, and laser reactivation/healing is suitable for fabricating highly efficient solar cells with p++-poly-Si/SiO2 contact passivation layers.Item Open Access Ultra-uniform perovskite crystals formed in the presence of tetrabutylammonium bistriflimide afford efficient and stable perovskite solar cells(2024) Lim, Jaekeun; Rafieh, Alwani Imanah; Shibayama, Naoyuki; Xia, Jianxing; Audinot, Jean-Nicolas; Wirtz, Tom; Kinge, Sachin; Glunz, Stefan W.; Ding, Yong; Ding, Bin; Kim, Hobeom; Saliba, Michael; Fei, Zhaofu; Dyson, Paul J.; Nazeeruddin, Mohammad Khaja; Kanda, HiroyukiCompositional engineering of organic–inorganic metal halide perovskite allows for improved optoelectrical properties, however, phase segregation occurs during crystal nucleation and limits perovskite solar cell device performance. Herein, we show that by applying tetrabutylammonium bistriflimide as an additive in the perovskite precursor solution, ultra-uniform perovskite crystals are obtained, which effectively increases device performance. As a result, power conversion efficiencies (PCEs) of 24.5% in a cell and 21.2% in a module are achieved, together with high stability under illumination, humidity and elevated thermal conditions.Item Open Access All-inorganic CsPbI2Br perovskite solar cells with thermal stability at 250 °C and moisture-resilience via polymeric protection layers(2025) Roy, Rajarshi; Byranvand, Mahdi Malekshahi; Zohdi, Mohamed Reza; Magorian Friedlmeier, Theresa; Das, Chittaranjan; Hempel, Wolfram; Zuo, Weiwei; Kedia, Mayank; Rendon, Jose Jeronimo; Boehringer, Stephan; Hailegnanw, Bekele; Vorochta, Michael; Mehl, Sascha; Rai, Monika; Kulkarni, Ashish; Mathur, Sanjay; Saliba, MichaelAll-inorganic perovskites, such as CsPbI2Br, have emerged as promising compositions due to their enhanced thermal stability. However, they face significant challenges due to their susceptibility to humidity. In this work, CsPbI2Br perovskite is treated with poly(3-hexylthiophen-2,5-diyl) (P3HT) during the crystallization resulting in significant stability improvements against thermal, moisture and steady-state operation stressors. The perovskite solar cell retains ∼90% of the initial efficiency under relative humidity (RH) at ∼60% for 30 min, which is among the most stable all-inorganic perovskite devices to date under such harsh conditions. Furthermore, the P3HT treatment ensures high thermal stress tolerance at 250 °C for over 5 h. In addition to the stability enhancements, the champion P3HT-treated device shows a higher power conversion efficiency (PCE) of 13.5% compared to 12.7% (reference) with the stabilized power output (SPO) for 300 s. In addition, the P3HT-protected perovskite layer in ambient conditions shows ∼75% of the initial efficiency compared to the unprotected devices with ∼28% of their initial efficiency after 7 days of shelf life.Item Open Access Mitigating the amorphization of perovskite layers by using atomic layer deposition of alumina(2025) Kedia, Mayank; Das, Chittaranjan; Kot, Malgorzata; Yalcinkaya, Yenal; Zuo, Weiwei; Tabah Tanko, Kenedy; Matvija, Peter; Ezquer, Mikel; Cornago, Iñaki; Hempel, Wolfram; Kauffmann, Florian; Plate, Paul; Lira-Cantu, Monica; Weber, Stefan A. L.; Saliba, MichaelAtomic layer deposition of aluminum oxide (ALD-Al2O3) layers has recently been studied for stabilizing perovskite solar cells (PSCs) against environmental stressors, such as humidity and oxygen. In addition, the ALD-Al2O3 layer acts as a protective barrier, mitigating pernicious halide ion migration from the perovskite towards the hole transport interface. However, its effectiveness in preventing the infiltration of ions and additives from the hole-transport layer into perovskites remains insufficiently understood. Herein, we demonstrate the deposition of a compact ultrathin (∼0.75 nm) ALD-Al2O3 layer that conformally coats the morphology of a triple-cation perovskite layer. This promotes an effective contact of the hole transporter layer on top of the perovskite, thereby improving the charge carrier collection between these two layers. Upon systematically investigating the layer-by-layer structure of the PSC, we discovered that ALD-Al2O3 also acts as a diffusion barrier for the degraded species from the adjacent transport layer into the perovskite. In addition to these protective considerations, ALD-Al2O3 impedes the transition of crystalline perovskites to an undesired amorphous phase. Consequently, the dual functionality (i.e., enhanced contact and diffusion barrier) of the ALD-Al2O3 protection enhanced the device performance from 19.1% to 20.5%, while retaining 98% of its initial performance compared to <10% for pristine devices after 1500 h of outdoor testing under ambient conditions. Finally, this study deepens our understanding of the mechanism of ALD-Al2O3 as a two-way diffusion barrier, highlighting the multifaceted role of buffer layers in interfacial engineering for the long-term stability of PSCs.Item Open Access Towards sustainable sulfide‐based all‐solid‐state‐batteries : an experimental investigation of the challenges and opportunities using solid electrolyte free silicon anodes(2024) Neumann, Tobias; Alexander Dold, Lukas; Thomas Cerny, Alain; Tröster, Eric; Günthel, Michael; Fischer, Anna; Peter Birke, Kai; Krossing, Ingo; Biro, DanielSilicon is one of the most promising anode active materials for future high–energy lithium‐ion‐batteries (LIB). Due to limitations related to volume changes during de-/lithiation, implementation of this material in commonly used liquid electrolyte‐based LIB needs to be accompanied by material enhancement strategies such as particle structure engineering. In this work, we showcase the possibility to utilize pure silicon as anode active material in a sulfide electrolyte‐based all‐solid‐state battery (ASSB) using a thin separator layer and LiNi0.6Mn0.2Co0.2O2 cathode. We investigate the integration of both solid electrolyte blended anodes and solid electrolyte free anodes and explore the usage of non‐toxic and economically viable solvents suitable for standard atmospheric conditions for the latter. To give an insight into the microstructural changes as well as the lithiation path inside the anode soft X‐ray emission and X‐ray photoelectron spectroscopy were performed after the initial lithiation. Using standard electrochemical analysis methods like galvanostatic cycling and impedance spectroscopy, we demonstrate that both anode types exhibit commendable performance as structural distinctions between two‐dimensional and three‐dimensional interfaces became evident only at high charge rates (8 C).Item Open Access A dual‐layered anode buffer layer structure for all solid‐state batteries(2024) Lu, Yushi; Chang, Hansen Michael; Birke, Kai PeterOver the past few decades, lithium‐ion batteries have garnered considerable attention, especially for their use in electric vehicles (EVs). In recent years, solid‐state batteries have become increasingly popular due to their excellent safety features and potential for high energy density. However, solid‐state batteries with lithium metal anodes present challenges in terms of electrochemical reactivity and cost. To address these challenges, alternative anode systems such as the “anode‐free” approach are being explored. In this study, we introduced a dual‐layered anode comprising a primary layer of physically vapor‐deposited zinc and a secondary layer of carbon black, focusing on investigating the influence of varying thicknesses of the lithiophilic zinc layer on cell cycling performance. Among the three different zinc thicknesses chosen for this purpose - categorized as thin (286 nm), medium (1.802 μm), and thick (6.519 μm) - the dual‐layered anode buffer layer was analyzed in a single‐layer full pouch cell. An in‐depth investigation into the lithium‐zinc alloying behavior was conducted through post‐mortem analysis. From the results, we found that the combination of the zinc layer with the carbon black layer improved cell cycling performance in terms of discharge capacity retention compared to a single layer of either zinc or carbon black. The cycling performance of this dual‐layered anode could be further enhanced by optimizing the zinc layer thickness, likely due to the irreversible alloying step of zinc and lithium. Among the various thicknesses evaluated, the thin zinc layer (286 nm) combined with the carbon black layer demonstrated the most promising cycling performance in all solid‐state batteries.Item Open Access Novel approach to diagnose safe electrical power distribution(2024) Braun, Lars; Le, Minh; Motz, Jürgen; Birke, Kai PeterThe integrity of the 12Vdcpower distribution system on a vehicle is essential to guarantee continuous power supply to safety-relevant consumers. Safety-relevant consumers are critical loads, for example, electric power steering, braking systems with functionalities like Anti-Lock Braking or Electronic Stability Control, and autonomous drive systems. To prevent insufficient power supply for safety-relevant consumers due to an increased wiring harness resistance, a novel diagnostic approach is developed to determine the condition of the power distribution, especially the electrical resistance. The influence of measurement errors and bus commutation on the estimation is investigated by using a simulation. By using the diagnostic, a resistance determination in the milliohm range with a standard deviation of σ=0.3mΩcan be achieved under realistic conditions. This ensures that failures in the wiring harness can be identified, avoiding cascading effects and minimizing recalls. Compared to the state of the art, redundancies, costs, and weight can be saved with the proposed diagnostic system based on electrical resistance estimation.