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 Top‐down approach to study chemical and electronic properties of perovskite solar cells : sputtered depth profiling versus tapered cross‐sectional photoelectron spectroscopies(2021) Das, Chittaranjan; Zia, Waqas; Mortan, Claudiu; Hussain, Navid; Saliba, Michael; Ingo Flege, Jan; Kot, MałgorzataA study of the chemical and electronic properties of various layers across perovskite solar cell (PSC) stacks is challenging. Depth‐profiling photoemission spectroscopy can be used to study the surface, interface, and bulk properties of different layers in PSCs, which influence the overall performance of these devices. Herein, sputter depth profiling (SDP) and tapered cross‐sectional (TCS) photoelectron spectroscopies (PESs) are used to study highly efficient mixed halide PSCs. It is found that the most used SDP‐PES technique degrades the organic and deforms the inorganic materials during sputtering of the PSCs while the TCS‐PES method is less destructive and can determine the chemical and electronic properties of all layers precisely. The SDP‐PES dissociates the chemical bonding in the spiro‐MeOTAD and perovskite layer and reduces the TiO2, which causes the chemical analysis to be unreliable. The TCS‐PES revealed a band bending only at the spiro‐MeOTAD/perovskite interface of about 0.7 eV. Both the TCS and SDP‐PES show that the perovskite layer is inhomogeneous and has a higher amount of bromine at the perovskite/TiO2 interface.Item Open Access Fourier spotting : a novel setup for single-color reflectometry(2022) Siegel, Johannes; Berner, Marcel; Werner, Jürgen H.; Proll, Günther; Fechner, Peter; Schubert, MarkusSingle-color reflectrometry is a sensitive and robust detection method in optical biosensor applications, for example for bioanalysis. It is based on the interference of reflected monochromatic radiation and is label free. We present a novel setup for single-color reflectometry based on the patented technology of Berner et al. from 2016. Tilting areas of micro-mirrors allow us to encode the optical reflection signal of an analyte and reference channel into a particular carrier frequency with the amplitude being proportional to the local reflection. Therefore, a single photodiode is sufficient to collect the signals from both channels simultaneously. A 180∘ phase shift in the tilt frequency of two calibrated micro-mirror areas leads to a superposition of the analyte and reference signal which enables an efficient reduction of the baseline offset and potential baseline offset drift. A performance test reveals that we are able to detect changes of the refractive index n down to Δn < 0.01 of saline solutions as regents. A further test validates the detection of heterogeneous binding interaction. This test compromises immobilized testosterone-bovine serum albumin on a three-dimensional layer of biopolymer as ligand and monoclonal anti-testosterone antibodies as analyte. Antibody/antigen binding induces a local growth of the biolayer and change in the refractive index, which is measured via the local change of the reflection. Reproducible measurements enable for the analysis of the binding kinetics by determining the affinity constant KA = 1.59 × 10- 7 M- 1. In summary, this work shows that the concept of differential Fourier spotting as novel setup for single-color reflectometry is suitable for reliable bioanalysis.Graphical AbstractItem Open Access Ionic liquid Stabilizing high‐efficiency tin halide perovskite solar cells(2021) Li, Guixiang; Su, Zhenhuang; Li, Meng; Yang, Feng; Aldamasy, Mahmoud H.; Pascual, Jorge; Yang, Fengjiu; Liu, Hairui; Zuo, Weiwei; Di Girolamo, Diego; Iqbal, Zafar; Nasti, Giuseppe; Dallmann, André; Gao, Xingyu; Wang, Zhaokui; Saliba, Michael; Abate, AntonioTin halide perovskites attract incremental attention to deliver lead‐free perovskite solar cells. Nevertheless, disordered crystal growth and low defect formation energy, related to Sn(II) oxidation to Sn(IV), limit the efficiency and stability of solar cells. Engineering the processing from perovskite precursor solution preparation to film crystallization is crucial to tackle these issues and enable the full photovoltaic potential of tin halide perovskites. Herein, the ionic liquid n‐butylammonium acetate (BAAc) is used to tune the tin coordination with specific O…Sn chelating bonds and NH…X hydrogen bonds. The coordination between BAAc and tin enables modulation of the crystallization of the perovskite in a thin film. The resulting BAAc‐containing perovskite films are more compact and have a preferential crystal orientation. Moreover, a lower amount of Sn(IV) and related chemical defects are found for the BAAc‐containing perovskites. Tin halide perovskite solar cells processed with BAAc show a power conversion efficiency of over 10%. This value is retained after storing the devices for over 1000 h in nitrogen. This work paves the way toward a more controlled tin‐based perovskite crystallization for stable and efficient lead‐free perovskite photovoltaics.Item Open Access Photoelectrochemical water‐splitting using CuO‐based electrodes for hydrogen production : a review(2021) Siavash Moakhar, Roozbeh; Hosseini‐Hosseinabad, Seyed Morteza; Masudy‐Panah, Saeid; Seza, Ashkan; Jalali, Mahsa; Fallah‐Arani, Hesam; Dabir, Fatemeh; Gholipour, Somayeh; Abdi, Yaser; Bagheri‐Hariri, Mohiedin; Riahi‐Noori, Nastaran; Lim, Yee‐Fun; Hagfeldt, Anders; Saliba, MichaelThe cost‐effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water‐splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO‐based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water‐splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO‐based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent‐generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.Item Open Access High‐stable lead‐free solar cells achieved by surface reconstruction of quasi‐2D tin‐based perovskites(2023) Yang, Feng; Zhu, Rui; Zhang, Zuhong; Su, Zhenhuang; Zuo, Weiwei; He, Bingchen; Aldamasy, Mahmoud Hussein; Jia, Yu; Li, Guixiang; Gao, Xingyu; Li, Zhe; Saliba, Michael; Abate, Antonio; Li, MengTin halide perovskites are an appealing alternative to lead perovskites. However, owing to the lower redox potential of Sn(II)/Sn(IV), particularly under the presence of oxygen and water, the accumulation of Sn(IV) at the surface layer will negatively impact the device's performance and stability. To this end, this work has introduced a novel multifunctional molecule, 1,4‐phenyldimethylammonium dibromide diamine (phDMADBr), to form a protective layer on the surface of Sn‐based perovskite films. Strong interactions between phDMADBr and the perovskite surface improve electron transfer, passivating uncoordinated Sn(II), and fortify against water and oxygen. In situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) analysis confirms the enhanced thermal stability of the quasi‐2D phase, and hence the overall enhanced stability of the perovskite. Long‐term stability in devices is achieved, retaining over 90% of the original efficiency for more than 200 hours in a 10% RH moisture N2 environment. These findings propose a new approach to enhance the operational stability of Sn‐based perovskite devices, offering a strategy in advancing lead‐free optoelectronic applications.Item Open Access Characterizing the influence of charge extraction layers on the performance of triple‐cation perovskite solar cells(2023) Siekmann, Johanna; Kulkarni, Ashish; Akel, Samah; Klingebiel, Benjamin; Saliba, Michael; Rau, Uwe; Kirchartz, ThomasSelecting suitable charge transport layers and suppressing non-radiative recombination at interfaces with the absorber layer is vital for maximizing the efficiency of halide perovskite solar cells. In this study, high-quality perovskite thin films and devices are fabricated with different fullerene-based electron transport layers and different self-assembled monolayers as hole transport layers. Then, a comparative study of a significant variety of different electrical, optical, and photoemission-based characterization techniques is performed to quantify the properties of the solar cells, individual layers, and, importantly, the interfaces between them. In addition, the limitations and problems of the different measurements, the insights gained by combining different methods, and the different strategies for extracting information from the experimental raw data, are highlighted.Item Open Access Novel approach to ensure safe power supply for safety-relevant consumers(2022) Braun, Lars; Le, Minh; Motz, Jürgen; Birke, Kai PeterThe 12 V powernet in vehicles must fulfill certain safety requirements due to the safety demand of consumers. A potential risk is undervoltage for a safety-relevant consumer, which leads to its fault. Therefore, a novel approach is presented in this study, which can predict the minimum terminal voltage for consumers. This consists of diagnostics of the wiring harness and of the lead-acid battery as well as predefined consumer currents. Using simulation, first the beginning of a drive cycle is simulated to determine the state of the powernet, and afterwards a critical driving maneuver is simulated to validate the predicted minimum terminal voltage. It demonstrates that the novel approach is able to predict a fault due to undervoltage. In addition to fulfilling safety requirements, the novel approach could be used to achieve additional availability and miniaturization of powernet components compared to the state of the art.Item Open Access Solar cells with laser doped boron layers from atmospheric pressure chemical vapor deposition(2022) Zapf-Gottwick, Renate; Seren, Sven; Fernandez-Robledo, Susana; Wete, Evariste-Pasky; Schiliro, Matteo; Hassan, Mohamed; Mihailetchi, Valentin; Buck, Thomas; Kopecek, Radovan; Köhler, Jürgen; Werner, Jürgen H.We present laser-doped interdigitated back contact (IBC) solar cells with efficiencies of 23% on an area of 244 cm2 metallized by a screen-printed silver paste. Local laser doping is especially suited for processing IBC cells where a multitude of pn-junctions and base contacts lay side by side. The one-sided deposition of boron-doped precursor layers by atmospheric pressure chemical vapor deposition (APCVD) is a cost-effective method for the production of IBC cells without masking processes. The properties of the laser-doped silicon strongly depend on the precursor’s purity, thickness, and the total amount of boron dopants. Variations of the precursor in terms of thickness and boron content, and of the laser pulse energy density, can help to tailor the doping and sheet resistance. With saturation-current densities of 70 fA/cm2 at sheet resistances of 60 Ohm/sq, we reached maximum efficiencies of 23% with a relatively simple, industrial process for bifacial IBC-cells, with 70% bifaciality measured on the module level. The APCVD-layers were deposited with an inline lab-type system and a metal transport belt and, therefore, may have been slightly contaminated, limiting the efficiencies when compared to thermal-diffused boron doping. The use of an industrial APCVD system with a quartz glass transport system would achieve even higher efficiencies.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.