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Wafer‐bonded two‐terminal III‐V//Si triple‐junction solar cell with power conversion efficiency of 36.1% at AM1.5g
Full text linkIn this work, we present the fabrication and analysis of a wafer-bonded GaInP/GaInAsP//Si triple-junction solar cell with 36.1% conversion efficiency under AM1.5g spectral illumination. The new cell design presents an improvement over previous III-V//Si triple-junction cells by the implementation of a rear-heterojunction for the middle cell. Furthermore, an advanced metallodielectric rear-side grating was used for light trapping enhancement in the silicon bottom cell that increased the silicon subcell current by 1.4 mA/cm2. The external radiative efficiency was quantified to be 1.5 times higher compared to a reference device with a GaInAsP homojunction middle cell. A luminescent coupling factor of 0.46 between the middle and bottom subcell was determined. The share of recombination in the space-charge region was experimentally shown to be insignificant as intended by the rear-heterojunction design. Overall, the open-circuit voltage of the middle cell increased by 61 mV compared to the previous generation. Given the established long-term stability of III-V and silicon-based solar cells, these results are promising steps towards the future employment of III-V/Si tandem solar cells
Hyphal exploration strategies and habitat modification of an arbuscular mycorrhizal fungus in microengineered soil chips
Full text linkArbuscular mycorrhizal fungi (AMF) are considered ecosystem engineers, but the interactions of their mycelium with their immediate surroundings are largely unknown. In this study, we used microfluidic chips, simulating artificial soil structures, to study foraging strategies and habitat modification of Rhizophagus irregularis symbiotically associated to carrot roots. AMF hyphae foraged over long distances in nutrient-void spaces, preferred straight over tortuous passages, anastomosed and showed strong inducement of branching when encountering obstacles. We measured bi-directional transport of cellular content inside active hyphae and documented strategic allocation of biomass within the mycelium via cytoplasm retraction from inefficient paths. R. irregularis modified pore-spaces in the chips by clogging pores with irregularly shaped spores. We suggest that studying AMF hyphal behaviour in spatial settings can explain phenomena reported at bulk scale such as AMF modification of water retention in soils. The use of microfluidic soil chips in AMF research opens up novel opportunities to study their ecophysiology and interactions with both biotic and abiotic factors
Direct linearly polarized electroluminescence from perovskite nanoplatelet superlattices
Full text linkPolarized light is critical for a wide range of applications, but is usually generated by filtering unpolarized light, which leads to substantial energy losses and requires additional optics. Here we demonstrate the direct emission of linearly polarized light from light-emitting diodes made of CsPbI3 perovskite nanoplatelet superlattices. The use of solvents with different vapour pressures enables the self-assembly of the nanoplatelets with fine control over their orientation (either face-up or edge-up) and therefore their transition dipole moment. As a result of the highly uniform alignment of the nanoplatelets, as well as their strong quantum and dielectric confinement, large exciton fine-structure splitting is achieved at the film level, leading to pure red light-emitting diodes with linearly polarized electroluminescence exhibiting a high degree of polarization of 74.4% without any photonic structures. This work demonstrates the potential of perovskite nanoplatelets as a promising source of linearly polarized light, opening up the development of next-generation three-dimensional displays and optical communications from a highly versatile, solution-processable system
Robust Phototaxis by Harnessing Implicit Communication in Modular Soft Robotic Systems
Full text linkIn robotics, achieving adaptivity in complex environments is challenging. Traditional robotic systems use stiff materials and computationally expensive centralized controllers, while nature often favors soft materials and embodied intelligence. Inspired by nature's distributed intelligence, this study explores a decentralized approach for robust behavior in soft robotic systems without knowledge of their shape or environment. It is demonstrated that only a few basic rules implemented in identical modules that shape the soft robotic system can enable whole-body phototaxis, navigating on a surface toward a light source, without explicit communication between modules or prior system knowledge. The results reveal the method's effectiveness in generating robust and adaptive behavior in dynamic and challenging environments. Moreover, the approach's simplicity makes it possible to illustrate and understand the underlying mechanism of the observed behavior, paying particular attention to the geometry of the assembled system and the effect of learning parameters. Consequently, the findings offer insights into the development of adaptive, autonomous robotic systems with minimal computational power, paving the way for robust and useful behavior in soft and microscale robots, as well as robotic matter, that operate in real-world environments
Magnetization Switching of Single Magnetite Nanoparticles Monitored Optically
Full text linkMagnetic nanomaterials record information as fast as picoseconds in computer memories but retain it for millions of years in ancient rocks. This exceedingly broad range of times is covered by hopping over a potential energy barrier through temperature, ultrafast optical excitation, mechanical stress, or microwaves. As switching depends on nanoparticle size, shape, orientation, and material properties, only single-nanoparticle studies can eliminate the ensemble heterogeneity. Here, we push the sensitivity of photothermal magnetic circular dichroism down to individual 20 nm magnetite nanoparticles. Single-particle magnetization curves display superparamagnetic to ferromagnetic behaviors, depending on the size, shape, and orientation. Some nanoparticles undergo thermally activated switching on time scales of milliseconds to minutes. Surprisingly, the switching barrier varies with time, leading to dynamical heterogeneity, a phenomenon familiar in protein dynamics and supercooled liquids. Our observations will help to identify the external parameters influencing magnetization switching and, eventually, to control it, an important step for many applications
Angular Dispersion of Free-Electron-Light Coupling in an Optical Fiber-Integrated Metagrating
Full text linkFree electrons can couple to optical material excitations on nanometer-length and attosecond-time scales, opening-up unique opportunities for both the generation of radiation and the manipulation of the electron wave function. Here, we exploit the Smith-Purcell effect to experimentally study the coherent coupling of free electrons and light in a circular metallo-dielectric metagrating that is fabricated onto the input facet of a multimode optical fiber. Using hyperspectral angle-resolved (HSAR) far-field imaging inside a scanning electron microscope, we probe the angular dispersion of Smith-Purcell radiation (SPR) that is simultaneously generated in free space and inside the fiber by an electron beam that grazes the metagrating at a nanoscale distance. Furthermore, we analyze the spectral distribution of SPR that is emitted into guided optical modes and correlate it with the numerical aperture of the fiber. By varying the electron energy between 5 and 30 keV, we observe the emission of SPR from the ultraviolet to the near-infrared spectral range, and up to the third emission order. In addition, we detect incoherent cathodoluminescence that is generated by electrons penetrating the input facet of the fiber and scattering inelastically. As a result, our HSAR measurements reveal a Fano resonance that is coupled to a Rayleigh anomaly of the metagrating, and that overlaps with the angular dispersion of second-order SPR at 20 keV. Our findings demonstrate the potential of optical fiber-integrated metasurfaces as a versatile platform to implement novel ultrafast light sources and to synthesize complex free-electron quantum states with light
Tuning the Optical and Structural Properties of Halide Perovskite by PbS Quantum Dot Additive Engineering for Enhanced Photovoltaic Performances
Full text linkThe combination of inorganic PbS quantum dots (QDs) and lead halide perovskite in one nanocomposite is considered as a promising approach to overcoming the limitations of metastable perovskites. However, to date, only a few examples of improved optoelectronic perovskites are realized with such materials. One of the keys to unraveling the full potential offered by the PbS QDs/perovskite material is the ability to purposefully modulate the interfacial electronic energy levels by changing the PbS QDs capping shell. Herein, this approach to adjust the offsets of the energy levels of the perovskite is demonstrated. To prepare the perovskite films with embedded PbS QDs, the organic capping of QDs is exchanged by a halide perovskite shell. Film properties are correlated to the structural changes of the soft perovskite matrix and their optical properties. Interestingly, this approach can be used to adjust the energy levels in the whole nanocomposite film, without changing the original bandgap, and thus paves the way for novel functional materials for optoelectronic devices. The applicability of this method is exemplified by fabricating solar cells with the perovskite nanocomposite, observing that the introduction of PbS/FAPI QDs into FAPI matrix boosts the average performance from 17.9% to 18.9% (21.3% champion device)
Stable developmental patterns of gene expression without morphogen gradients
Full text linkGene expression patterns in developing organisms are established by groups of crossregulating target genes that are driven by morphogen gradients. As development progresses, morphogen activity is reduced, leaving the emergent pattern without stabilizing positional cues and at risk of rapid deterioration due to the inherently noisy biochemical processes at the cellular level. But remarkably, gene expression patterns remain spatially stable and reproducible over long developmental time spans in many biological systems. Here we combine spatial-stochastic simulations with an enhanced sampling method (Non- Stationary Forward Flux Sampling) and a recently developed stability theory to address how spatiotemporal integrity of a gene expression pattern is maintained in developing tissue lacking morphogen gradients. Using a minimal embryo model consisting of spatially coupled biochemical reactor volumes, we study a prototypical stripe pattern in which weak crossrepression between nearest neighbor expression domains alternates with strong repression between next-nearest neighbor domains, inspired by the gap gene system in the Drosophila embryo. We find that tuning of the weak repressive interactions to an optimal level can prolong stability of the expression patterns by orders of magnitude, enabling stable patterns over developmentally relevant times in the absence of morphogen gradients. The optimal parameter regime found in simulations of the embryo model closely agrees with the predictions of our coarse-grained stability theory. To elucidate the origin of stability, we analyze a reduced phase space defined by two measures of pattern asymmetry. We find that in the optimal regime, intact patterns are protected via restoring forces that counteract random perturbations and give rise to a metastable basin. Together, our results demonstrate that metastable attractors can emerge as a property of stochastic gene expression patterns even without system-wide positional cues, provided that the gene regulatory interactions shaping the pattern are optimally tuned
Consistent Interpretation of Time- and Frequency-Domain Traces of Ion Migration in Perovskite Semiconductors
Full text linkThe migration of mobile ions through the metal halide perovskite layer is still one of the main reasons for the poor stability of perovskite solar cells, LEDs, and photodetectors. To characterize mobile ions in the perovskite layer, time- and frequency-based electrical measurements are promising techniques. However, the presence of transport layers complicates their interpretation, limiting the information about mobile ions that can be extracted, and it is not clear how different features in frequency- and time-domain measurements relate to mobile ions. Here, we characterize a transport-layer-free device with capacitance frequency, capacitance transient, and current transient measurements in the dark, under illumination, and at different temperatures. We extract characteristic ionic signatures from the measurements, which we reproduce with drift-diffusion simulations for each technique. This allows us to explain the origins of the different ionic signatures, advancing our understanding of how electronic characterization techniques can be used to study the properties of mobile ions
Roadmap for Optical Metasurfaces
Full text linkMetasurfaces have recently risen to prominence in optical research, providing unique functionalities that can be used for imaging, beam forming, holography, polarimetry, and many more, while keeping device dimensions small. Despite the fact that a vast range of basic metasurface designs has already been thoroughly studied in the literature, the number of metasurface-related papers is still growing at a rapid pace, as metasurface research is now spreading to adjacent fields, including computational imaging, augmented and virtual reality, automotive, display, biosensing, nonlinear, quantum and topological optics, optical computing, and more. At the same time, the ability of metasurfaces to perform optical functions in much more compact optical systems has triggered strong and constantly growing interest from various industries that greatly benefit from the availability of miniaturized, highly functional, and efficient optical components that can be integrated in optoelectronic systems at low cost. This creates a truly unique opportunity for the field of metasurfaces to make both a scientific and an industrial impact. The goal of this Roadmap is to mark this “golden age” of metasurface research and define future directions to encourage scientists and engineers to drive research and development in the field of metasurfaces toward both scientific excellence and broad industrial adoption