As silicon solar cells approach their theoretical efficiency limit, further performance gains become increasingly difficult. Two studies now demonstrate advances in mainstream tunnel oxide passivating contact technology: one improves the boron emitter and polysilicon in the standard design, while the other proposes an alternative cell architecture that overcomes limitations of the mainstream approach.

As the silver price sets one record height after another, to curb costs, the need to reduce silver consumption in solar cell metallization increases. This work develops front-side metallization for tunnel oxide passivating contact (TOPCon) solar cells toward fine-line printing, i.e., feature sizes of less than 20 mu m in width and a reduction of wet paste laydown. Besides silver reduction, this is motivated by increasing conversion efficiency, which further reduces cost per watt. To reach these goals by screen printing, three different fine-mesh configurations for knotless screens are utilized. Nominal screen opening widths vary from 24 & micro;m to 13 mu m. Moreover, printing with a dual-layer stencil featuring a nominal opening width of 9 mu m is analyzed. The printed and fired contacts are characterized toward key geometrical and electrical performance indicators. Based on the corresponding findings, M10-sized TOPCon solar cells featuring fine-line grids with a core finger width w(c) = (16 +/- 1) mu m were fabricated. Compared to the reference group with w(c) = (23 +/- 2) mu m, a conversion efficiency gain of (0.9 +/- 0.2)% (rel) is achieved, which is mainly driven by a reduction of shading-induced losses. Furthermore, wet paste laydown on the front is reduced by similar to 30% (rel) using such metallization.

As tunnel oxide passivated contact (TOPCon) cell technology has established itself as the dominant cell technology in global photovoltaic production, this study investigates competing architectures, including TOPCoRE (TOPCon with Rear Emitter), and local TOPCon(2) (passivated contacts on both sample sides), to identify paths for enhancing power output by improving the cells' front side. The authors conduct a comprehensive simulation analysis using Quokka3, with input parameters derived from internal measurements and published data. While pointing out the necessary surface parameters to achieve a certain cell efficiency evolution, the sensitivity of the cell concepts to wafer quality, base resistance, and minority carrier lifetime is evaluated. The results indicate that the TOPCoRE concept on p-type wafers can be a strong contender to the standard iTOPCon, reaching 26%+ efficiency, if equally high electrical wafer quality can be achieved. The findings highlight the importance of further optimization paths, with local Front Surface Fields or local front TOPCon layers, demonstrating potential efficiencies of up to 26.5% and more.

Within this work, we present key results of the transnational European research project “Bussard”. The aim of this project is the development and evaluation of various innovative approaches for highly efficient cell concepts such as tunnel oxide passivating contact (TOPCon) solar cells considering the whole process chain including front-end, back-end and module processing. We present atomic layer deposition (ALD) as a high-throughput alternative for the deposition of Al2O3 passivation layers on the front side of TOPCon solar cells enabling a substantial reduction of the emitter saturation current density down to j0e = 13 fA/cm2. In the field of metallization, we evaluate and demonstrate three innovative approaches for the fine-line metallization of TOPCon solar cells. In this study we focus on multi-nozzle parallel dispensing, a technology that was developed as an alternative to standard screen-printing metallization and is used for the metallization of TOPCon solar cells for the first time. By optimizing the fabrication process at Fraunhofer ISE, we realize TOPCon solar cells (156.75 mm × 156.75 mm) with a champion conversion efficiency of up to ηmax = 24.2% (independently confirmed by Fraunhofer ISE CalLab PVCells). Finally, we present a comprehensive evaluation of the innovative Tape Solution interconnection concept for TOPCon cells and modules. We demonstrate the feasibility on small-scale and full-format modules and analyze the I–V results as well as cell-to-module (CTM) loss analysis using the simulation tool SmartCalc®. The results are compared to TOPCon modules interconnected via SmartWire Connection Technology (SWCT) and electrically conductive adhesive (ECA).

In this work, we investigate different front-side passivation approaches for p-type IBC solar cells. We compare a POCl3-diffused and SiNx-passivated front floating emitter (FFE) with an undiffused front surface passivated by a layer stack of aluminum oxide Al2O3 and silicon nitride SiNx, using different technologies for Al2O3 deposition. Further, we investigate a boron-doped front surface field (FSF), realized with different BBr3 diffusion approaches. We achieve promising implied open-circuit voltages iVoc of up to 740 mV with Al2O3/SiNx-passivation, which is a 7 mV increase compared to the reference process using the phosphorus-doped FFE. Further, we fabricated boron-doped FSF samples exhibiting promising recombination parameters of j0 < 6 fA/cm2. The transfer of the Al2O3/SiNx-passivation into pIBC solar cells already reaches peak efficiencies of h = 23.3%, comparable to the FFE.

The ability to gather information about materials and products, such as their origin, physicochemical properties or history of experienced environmental stimuli, is valuable for quality control, predictive maintenance, delivery tracking, recycling, and more. Integrating additives capable of recording and storing information into materials offers a flexible approach to create "materials intelligence". Common strategies utilize luminescent markers or DNA sequences that enable object identification and environmental impact monitoring. In contrast to optical methods limited to surface-level analysis, magnetic fields penetrate materials, enabling nondestructive readout even from the inside of opaque or multicomponent objects. While magnetic particle technologies have traditionally been used for biosensing and imaging with highly sensitive instruments like magnetic resonance imaging, these methods are unsuitable for quick, on-site analysis of macroscopic objects. During the past decade, magnetic particle spectroscopy (MPS) has emerged as a faster and more accessible characterization technique. MPS measures the magnetic response of particles in ambient conditions under alternating fields, offering high temporal resolution (∼1-10 s) and more geometric freedom than other magnetometry techniques. Magnetic nanoparticles are a widely studied material class that have been synthesized and optimized, e.g., for various MPS-based application scenarios and to obtain fundamental understanding of magnetic particle systems. Supraparticles (SPs) represent the next structural hierarchy level, as they are composed of one or multiple types of (magnetic) nanoparticles in a defined particulate structure. By ingenious control of structure and composition of such SPs, we have shown that various kinds of information can be obtained from them upon readout with MPS. In this Account, we present SP design concepts facilitating to obtain information about environmental stimuli (e.g., temperature, moisture, UV light, chemical gases) based on irreversible spectral magnetic signal changes upon readout with MPS. Initially, the state of the art on nanoparticles, which provide information by stimulus-induced agglomeration, is summarized. Subsequently, SPs consisting of multiple different nanoparticle types and their capabilities to obtain information on environmental stimuli are considered. Specifically, the advantages of using one or more signal transducing magnetic nanoparticle types used in conjunction with one or more nonmagnetic secondary materials susceptible to the desired environmental stimuli (sensitizer) are discussed. Finally, our latest findings on pronounced large-scale SP structure formation (millimeter-scale) through strongly interacting SPs and their implications on the integration of SPs in macroscopic objects of interest are described. Each of the three structural hierarchy levels, namely nanoparticles, SPs, and the macroscopic object of interest, represents an opportunity on the material level to fine-tune magnetic interactions. However, since the magnetic interactions across these three structural hierarchy levels are interdependent, meaning changes at the nanoparticle level influence the interactions of SPs at the macroscopic level, their control and interpretation in MPS remain challenging and prone to misinterpretation. The application of magnetic SPs as information-providing additives for predictive maintenance, material reuse, recycling, and industrial digitization requires a thorough understanding of all three hierarchical levels. Only then can suitable materials and processes be developed, turning challenges into opportunities for transforming passive matter into perceptual, information-providing systems through the integration of magnetic SPs.

This study presents nanosized metal‐organic framwork (nanoMOF)‐based multifunctional mixed‐matrix‐membranes (MMMs) and composite powders as extremely sensitive responder materials for a responder‐stimulus based multilevel anti‐counterfeiting. The physicochemical properties of nanoMOF‐based composites offer a wide operational range as anti‐counterfeiting tags. Nine responder materials are presented, constituted of trivalent lanthanide‐containing nanoMOFs ([Ln 3 (bdc) 4.5 (H 2 O) 3 (dmf) 2 ] (nLn‐bdc); bdc 2− ═benzene‐1,4‐dicarboxylate; Ln═Eu, Tb, Yb) and polystyrene sulfonate, pyrolyzed resorcinol‐formaldehyde and polysulfone as matrices. These materials inherit distinct properties, and their combination provides visible and near‐infrared light emission and specific conductivity for multiple security level anti‐counterfeiting. The additive and interdependent nature of security features in the developed anti‐counterfeiting materials ensures that altering one feature will invariably affect others, thereby reinforcing the overall integrity and resilience of the security mechanism. Even the pitch‐black composites of nLn‐bdc and pyrolyzed resorcinol‐formaldehyde show bright light emission to the near‐infrared range, when stimulated by UV‐light being suitable for black materials. This work also describes a matrix‐based active contribution as security feature to an anti‐counterfeiting tag, instead of being solely used as a carrier for the security feature‐bearing nanoMOFs. The combination of multiple levels of security by different properties marks these multifunctional composites as anti‐counterfeiting materials being complicated to copy including a proof‐of‐principle experiment.

P-type interdigitated back contact (pIBC) solar cells represent a promising alternative to the currently dominant Tunnel Oxide Passivated Contact (TOPCon) technology, utilizing the industrially established metallization scheme of Passivated Emitter and Rear Cells (PERC) for the p-type base while incorporating TOPCon metallization for the n-type polycrystalline emitter. In this study, we present the results of optimization efforts aimed at increasing the efficiency pIBC cells manufactured in our lab by minimizing metallization-induced losses. Aluminum pastes with varying silicon content were used, and the firing temperature was adjusted. These modifications resulted in a reduction in the metallization-induced Voc​ loss after aluminum metallization to 5 mV, along with contact resistance values below 1 mΩ.cm². Additionally, reducing the n-polySi thickness led to a decrease in free carrier absorption and an increase in Jsc​. Finally, we achieved non-metallized cell precursors exhibiting iVoc​ values between 730 and 740 mV and a champion solar cell efficiency of 23.3%.

Magnetic supraparticles (SPs) can be employed as micron-sized particulate additives in arbitrary objects to serve as ID-tag or recorder of environmental triggers. Combined with magnetic particle spectroscopy (MPS), which enables read-out of the magnetic information in ambient conditions within seconds, magnetic SPs represent a powerful approach to equip materials with information. The encoded information relies on magnetic interactions within the SPs (intra-SP interactions) of chosen nanoparticles (NPs). However, possible magnetic interactions between SPs (inter-SP interactions), that might alter the MPS signal as well, have been neglected so far. Herein, it is elucidated that significant inter-SP interactions exist and that they can be tailored via adjustments in the SP structure, i.e., by defined adjustments of their intra-interaction as revealed by 3D-MuMax simulations and experiments in viscous fluids. Superparamagnetic iron oxide nanoparticle-based SP powders with strong inter-SP interactions exhibit significantly different MPS signals compared to their state after being incorporated into a matrix. Powders with weak inter-SP interactions (achieved by integration of non-magnetic SiO2 nanoparticles) show almost no signal change before and after incorporation. Both extremes of inter-SP interactions can be beneficial for various application scenarios and can be tailored on the nano-scale due to the interdependency of intra- and inter-SP interactions.

Minimizing carrier recombination in silicon solar cells is key to increase the conversion efficiency, as recombination affects both the fill factor and the open circuit voltage. Recombination at metal-semiconductor interfaces plays a crucial part in this, however, processing conditions which lead to low recombination, such as e.g., a low firing set temperature or the use of thick dielectrics, typically result in increased contact resistivities. Also, a too low firing set temperature leads to an incomplete hydrogenation of the interfaces. Recently, laser-enhanced contact optimization has been introduced to decouple recombination and contact properties to some extent, which allows for high fill factors and high open circuit voltages, and which explains the growing interest from manufacturers in that technology. We elucidate on the need for improved hydrogenation of interfaces, which contradicts the wish to decrease firing temperatures for reduced carrier recombination at metal-semiconductor interfaces. The implementation of an additional annealing step, e.g. in a tube furnace, after dielectric surface passivation is shown to lead to improved passivation properties so that the thermal budget during contact firing can be optimized to minimize contact resistivities. Overall, contact optimization allows for solar cell efficiencies of 24.1%, measured at an industrial cell tester, for a traditional approach without additional annealing step, and applying an AgAl front side metallization paste. A comparison of Ag and AgAl front side metallization pastes reveals a higher open circuit voltage for the Ag paste, at the drawback of an increased contact resistivity.

Induction heating of composite materials is of great interest in fields such as controlled polymer curing or degradation, self-healing or contactless joining. Ferrimagnetic iron oxide nanoparticle (IONPs) are suitable candidates for a powder additive to provide this indictive heating functionality, while being low-cost, abundant and a well-studied material class. Varying IONP size, morphology or doping facilitate fine-tune heating properties. However, the interactions of such IONP additives in material composites are often neglected and can significantly alter the induction heating mechanism. In this work, we systematically vary the IONP interactions in polydimethylsiloxane composite materials by integrating 1.) dispersed IONPs 2.) supraparticles of IONPs (micrometer-assemblies), and 3.) oven-dried hard agglomerated IONPs. Additionally, these three levels of interaction are investigated for three different IONPs types (dodecahedrally and octahedrally shaped, as well as cobalt-doped). In general, dispersed IONPs reveal a broader hysteresis and therefor a faster heating curve. We highlight that not only IONP characteristics (size, morphology, doping), but also excitation field strength and foremost IONP interactions in the composite materials are parameters that are interdependent regarding induction heating and need to be considered as such for optimization in an application-oriented scenario.

In this study, the impact of tunnel oxide passivated contact (TOPCon) solar cell precursor structures on commercial Ga-doped Czochralski silicon is investigated regarding bulk- and surface-related degradation. Two sample types, symmetrical poly-Si structures and asymmetrical samples featuring various passivation stacks used in TOPCon cells are examined. It is found that firing temperatures well above 800 degrees C lead to blistering and a significant reduction in performance for symmetrical TOPCon structures, reducing iV(OC) to below 700 mV. Treatment at an elevated temperature under constant illumination revealed that a significant degradation could only be observed at measured firing peak temperatures above 750 degrees C. While it is found that an AlOx interlayer underneath a SiNy:H layer effectively reduces the extent of degradation without an (n)poly-Si layer, it seems to be less effective on top of (n)poly-Si layers. Another experiment on the long-term stability revealed that surface-related degradation (SRD) is significantly reduced by the usage of symmetrical TOPCon structures and for a sample passivated with an SiOz/AlOx/SiNy:H stack. Compared to reference samples processed without TOPCon structures, a notable reduction in the extent of light- and elevated temperature-induced degradation (LeTID) is achieved in the samples featuring TOPCon structures, which is due to less hydrogen in-diffusion from passivation layer stacks into the bulk during the firing process.

Superparamagnetic iron oxide nanoparticles (SPIONs) are prone to oxidation at elevated temperatures (>300 C-degrees) and lose their magnetizability upon transition from magnetite/maghemite (gamma-Fe2O3 / Fe3O4) to hematite (alpha-Fe2O3). Silica (SiO2) shells can effectively prevent this undesired effect up to approximate to 1000 C-degrees. Herein, the study shows how to utilize SPIONs with varying SiO2 shell thickness and thus, different oxidation susceptibility, and how to combine them in micrometers sized assemblies - so-called supraparticles (SPs), to create a structurally emerging magnetic temperature recording functionality. The desired oxidation of non or weakly-protected SPIONs within SPs upon temperature events reduces dipole-dipole interactions of well-protected SPIONs in the confined SP entity. The resulting change of magnetic interactions therefore contains information on the thermal history of the SP, which can be spectrally read out via magnetic particle spectroscopy within seconds. Their working range can be tuned from 400 to 1000 C-degrees on two independent structural hierarchy levels, namely the SiO2 shell thickness and the freely selectable ratios of different building blocks in the SP. The application of such SPs as particulate additives for magnetic recording of high-temperature events, especially relevant in metal, alloy, and ceramic processing, representing a yet unexplored and optically-independent option for bulk temperature recording is proposed.

The market share of low-cost battery chemistries, which offer little to no recycling profitability with current methods, is growing. Design for circularity could be the key to reducing costs and enhancing sustainability for these batteries.

To tailor superparamagnetic iron oxide nanoparticles (SPIONs) to the specific needs of diverse application fields, it is essential to understand not only their intrinsic properties but also their interactions with each other. Theoretical models predicting/explaining the magnetization behavior of macroscopic samples containing millions of SPIONs are intricate due to the complexity of the underlying relaxation mechanisms in alternating fields. This study introduces supraparticles (SPs) as model architectures to empirically investigate magnetic interactions within and between large SPION clusters (>100 nanoparticles (NPs)). For this purpose, NP dispersions containing SPIONs and silica (SiO2)NPs as non-magnetic building blocks are spray-dried to form binary SPs. Selective salt-induced agglomeration of the two building block types before spray-drying is utilized to tailor SP architectures, including control over SPION cluster size, shape, and proximity. Magnetic particle spectroscopy (MPS), operating under ambient conditions, reveals altered magnetization behavior for different cluster structures. Not only the nearest SPION neighbors, but the whole cluster structure up to several micrometers is decisive for the magnetization behavior. This highlights the importance of long-range magnetic interactions. This work presents a versatile approach for designing model architectures to advance empirical interaction studies between SPIONs in macroscopic samples.

The recombination parameter J 0 s provides an important metric to characterize surface recombination. For its calculation, numerous methods and models have to be applied. Since the models for the Auger and radiative recombination in crystalline silicon were recently revised, it is important to investigate the influence of these changes on J 0 s . The origin and possible ways of obtaining J 0 s from effective lifetime measurements as well as simulations are described in detail, including the potential to fit the full lifetime curve and a new approach that is based upon the reparameterization of the excess charge carrier density Δ n . Using the effective lifetime measurements, we find that J 0 s values determined with the older parameterization by Richter et al. will result in erroneous values up to 5 fA/cm 2 , depending on the chosen conditions. By simulating the recombination parameter J 0 s in near surface, highly doped structures, such as emitters, it is shown that these errors can even go up to 50%. If used in a simulation, we highlight the importance of having the parameterizations of surface recombination being determined with the corresponding parameterization of intrinsic recombination. Therefore, an update for the recombination at oxide-passivated and phosphorous doped surfaces is given that can be used with the new intrinsic recombination models. Finally, we give some best-practice examples on how recent improvements in effective lifetime measurements affect J 0 s values as well as possible pitfalls.

Oxygen precipitates are among the most detrimental oxygen‐related silicon bulk defects formed during solar cell manufacturing. These defects are formed only during high‐temperature processes, impeding an identification of prone materials during incoming inspection. Moreover, the prediction of oxygen‐precipitate‐related bulk charge carrier recombination currently requires advanced numerical simulation. This work presents an easily implementable model to predict the bulk carrier lifetime limit, using the temperature–time profile of a high‐temperature process as well as the material properties as the input data. In addition to published analytical descriptions of oxygen precipitation, an empirical description of the retarded growth of small precipitates is included. Furthermore, the time‐lag in nucleation is explicitly considered, which is, to our knowledge, not implemented in oxygen precipitation modeling so far. The calibration of the two free parameters of the model is achieved using the experimental data of 19 different thermal process combinations performed using a single material. This results in a good agreement not only for the material used for calibration but also for other silicon materials. A validation based on passivated emitter and rear cells as well as on test structures confirms the ability of the model to predict bulk carrier lifetimes after solar cell processing.

Most analytical techniques used to study the surface chemical properties of superparamagnetic iron oxide nanoparticles (SPIONs) are barely suitable for in situ investigations in liquids, where SPIONs are mostly applied for hyperthermia therapy, diagnostic biosensing, magnetic particle imaging or water purification. Magnetic particle spectroscopy (MPS) can resolve changes in magnetic interactions of SPIONs within seconds at ambient conditions. Herein, we show that by adding mono- and divalent cations to citric acid capped SPIONs, the degree of agglomeration can be utilized to study the selectivity of cations towards surface coordination motifs via MPS. A favored chelate agent, like ethylenediaminetetraacetic acid (EDTA) for divalent cations, removes cations from coordination sites on the SPION surface and causes redispersion of agglomerates. The magnetic determination thereof represents what we call a "magnetically indicated complexometric titration". The relevance of agglomerate sizes for the MPS signal response is studied on a model system of SPIONs and the surfactant cetrimonium bromide (CTAB). Analytical ultracentrifugation (AUC) and cryogenic transmission electron microscopy (cryo-TEM) reveal that large micron-sized agglomerates are required to significantly change the MPS signal response. With this work, a fast and easy-to-use characterization method to determine surface coordination motifs of magnetic nanoparticles in optically dense media is demonstrated.

Stacking of wafers for thermal processing enables a strong increase of the throughput and thus offers a high potential for cost reduction in solar cell production. In previous studies, the high temperature stack oxidation (HiTSOx) approach showed promising solar cell results and homogeneous thermal oxide growth over the wafer surface within the stack. In this work, we investigate the thermal oxide growth in the gap between stacked wafers where the wafer surfaces touching each other. We perform finite element method (FEM) simulation to identify the mechanism for the oxygen transport inside the gap and compare the simulated layer thickness to experimental data. In this simulation, the gap height is an important parameter. Therefore, we present a gravimetric-density approach to experimentally determine the gap height. Further, passivated emitter and rear (PERC) solar cells are fabricated using the HiTSOx approach. A high open-circuit voltage of Voc = 694 mV confirms the high quality of the surface passivation achieved in the stack oxidation.