Nanopatterned Back-Reflector with Engineered Near-Field/Far-Field Light Scattering for Enhanced Light Trapping in Silicon-Based Multijunction Solar Cells

Multijunction solar cells provide a path to overcome the efficiency limits of standard silicon solar cells by harvesting a broader range of the solar spectrum more efficiently. However, Si-based multijunction architectures are hindered by incomplete harvesting in the near-infrared (near-IR) spectral range as Si subcells have weak absorption close to the band gap. Here, we introduce an integrated near-field/far-field light trapping scheme to enhance the efficiency of silicon-based multijunction solar cells in the near-IR range. To achieve this, we design a nanopatterned diffractive silver back-reflector featuring a scattering matrix that optimizes trapping of multiply scattered light into a range of diffraction angles. We minimize reflection to the zeroth order and parasitic plasmonic absorption in silver by engineering destructive interference in the patterned back-contact. Numerical and experimental assessment of the optimal design on the performance of single-junction Si TOPCon solar cells highlights an improved external quantum efficiency over a planar back-reflector (+1.52 mA/cm2). Nanopatterned metagrating back-reflectors are fabricated on GaInP/GaInAsP//Si two-terminal triple-junction solar cells via substrate conformal imprint lithography and characterized optically and electronically, demonstrating a power conversion efficiency improvement of +0.9%abs over the planar reference. Overall, our work demonstrates the potential of nanophotonic light trapping for enhancing the efficiency of silicon-based multijunction solar cells, paving the way for more efficient and sustainable solar energy technologies.

Solving integral equations in free space with inverse-designed ultrathin optical metagratings

As standard microelectronic technology approaches fundamental limitations in speed and power consumption, novel computing strategies are strongly needed. Analogue optical computing enables the processing of large amounts of data at a negligible energy cost and high speeds. Based on these principles, ultrathin optical metasurfaces have been recently explored to process large images in real time, in particular for edge detection. By incorporating feedback, it has also recently been shown that metamaterials can be tailored to solve complex mathematical problems in the analogue domain, although these efforts have so far been limited to guided-wave systems and bulky set-ups. Here, we present an ultrathin Si metasurface-based platform for analogue computing that is able to solve Fredholm integral equations of the second kind using free-space visible radiation. A Si-based metagrating was inverse-designed to implement the scattering matrix synthesizing a prescribed kernel corresponding to the mathematical problem of interest. Next, a semitransparent mirror was incorporated into the sample to provide adequate feedback and thus perform the required Neumann series, solving the corresponding equation in the analogue domain at the speed of light. Visible wavelength operation enables a highly compact, ultrathin device that can be interrogated from free space, implying high processing speeds and the possibility of on-chip integration.

Optical Characterization of Plasmonic Indium Lattices Fabricated via Electrochemical Deposition

The optical properties of periodic metallic nanoparticle lattices have found many exciting applications. Indium is an emerging plasmonic material that offers to extend the plasmonic applications given by gold and silver from the visible to the ultraviolet spectral range, with applications in imaging, sensing, and lasing. Due to the high vapor pressure/low melting temperature of indium, nanofabrication of ordered metallic nanoparticles is nontrivial. In this work, we show the potential of selective area electrochemical deposition to generate large-area lattices of In pillars for plasmonic applications. We study the optical response of the In lattices by means of angle-dependent extinction measurements demonstrating strong plasmonic surface lattice resonances and a good agreement with numerical simulations. The results open avenues toward high-quality lattices of plasmonic indium nanoparticles and can be extended to other promising plasmonic materials that can be electrochemically grown.

Optically Resonant Bulk Heterojunction PbS Quantum Dot Solar Cell

We design an optically resonant bulk heterojunction solar cell to study optoelectronic properties of nanostructured p-n junctions. The nanostructures yield strong light-matter interaction as well as distinct charge-carrier extraction behavior, which together improve the overall power conversion efficiency. We demonstrate high-resolution substrate conformal soft-imprint lithography technology in combination with state-of-the art ZnO nanoparticles to create a nanohole template in an electron transport layer. The nanoholes are infiltrated with PbS quantum dots (QDs) to form a nanopatterned depleted heterojunction. Optical simulations show that the absorption per unit volume in the cylindrical QD absorber layer is enhanced by 19.5% compared to a planar reference. This is achieved for a square array of QD nanopillars of 330 nm height and 320 nm diameter, with a pitch of 500 nm on top of a residual QD layer of 70 nm, surrounded by ZnO. Electronic simulations show that the patterning results in a current gain of 3.2 mA/cm² and a slight gain in voltage, yielding an efficiency gain of 0.4%. Our simulations further show that the fill factor is highly sensitive to the patterned structure. This is explained by the electric field strength varying strongly across the patterned absorber. We outline a path toward further optimized optically resonant nanopattern geometries with enhanced carrier collection properties. We demonstrate a 0.74 mA/cm² current gain for a patterned cell compared to a planar cell in experiments, owing to a much improved infrared response, as predicted by our simulations.

Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission

Lead-halide perovskites offer excellent properties for lighting and display applications. Nanopatterning perovskite films could enable perovskite-based devices with designer properties, increasing their performance and adding novel functionalities. We demonstrate the potential of nanopatterning for achieving light emission of a perovskite film into a specific angular range by introducing periodic sol-gel structures between the injection and emissive layer by using substrate conformal imprint lithography (SCIL). Structural and optical characterization reveals that the emission is funnelled into a well-defined angular range by optical resonances, while the emission wavelength and the structural properties of the perovskite film are preserved. The results demonstrate a flexible and scalable approach to the patterning of perovskite layers, paving the way toward perovskite LEDs with designer angular emission patterns.

Observational study to estimate the proportion of surgical site infection following excision of ulcerated skin tumours (OASIS study)

BACKGROUND

Ulceration is a recognized risk factor for surgical site infection (SSI); however, the proportion of patients developing SSI after excision of an ulcerated skin cancer is unknown.

AIM

To determine the proportion of participants with SSI after surgical excision of an ulcerated skin cancer. A secondary aim was to assess feasibility outcomes to inform the design of a randomized controlled trial to investigate the benefits and harms of perioperative antibiotics following excision of ulcerated tumours.

METHODS

This was a multicentre, prospective, observational study of patients undergoing excision of an ulcerated skin cancer between March 2019 and March 2020. Prior to surgical excision, surface swabs of the ulcerated tumours of participants recruited from one centre were undertaken to determine organism growth. At 4 weeks after surgery, all participants were e-mailed or posted the Wound Healing Questionnaire (WHQ) to determine whether they had developed SSI.

RESULTS

In total, 148 participants were recruited 105 (70.9%) males; mean ± SD age 77.1 ± 12.3 years. Primary outcome data were available for 116 (78.4%) participants, of whom 35 (30.2%) were identified as having an SSI using the WHQ with a cutoff score of 8, and 47 (40.5%) were identified with a cutoff score of 6. Using the modified WHQ in participants with wounds left to heal by secondary intention, 33 (28.4%) and 43 (37.1%) were identified to have SSI respectively.

CONCLUSION

This prospective evaluation of SSI identified with the WHQ following excision of ulcerated skin cancers demonstrated a high proportion with SSI. The WHQ was acceptable to patients; however, further evaluation is required to ensure validity in assessing skin wounds.

High-Index Dielectric Metasurfaces Performing Mathematical Operations

Image processing and edge detection are at the core of several newly emerging technologies, such as augmented reality, autonomous driving, and more generally object recognition. Image processing is typically performed digitally using integrated electronic circuits and algorithms, implying fundamental size and speed limitations, as well as significant power needs. On the other hand, it can also be performed in a low-power analog fashion using Fourier optics, requiring, however, bulky optical components. Here, we introduce dielectric metasurfaces that perform optical image edge detection in the analog domain using a subwavelength geometry that can be readily integrated with detectors. The metasurface is composed of a suitably engineered array of nanobeams designed to perform either first- or second-order spatial differentiation. We experimentally demonstrate the second-derivative operation on an input image, showing the potential of all-optical edge detection using a silicon metasurface geometry working at a numerical aperture as large as 0.35.

Correction to: Bone marrow pericyte dysfunction in individuals with type 2 diabetes

Unfortunately, three errors were made in the conversion of HbA_1c to per cent values.

Bone marrow pericyte dysfunction in individuals with type 2 diabetes

AIMS/HYPOTHESIS

Previous studies have shown that diabetes mellitus destabilises the integrity of the microvasculature in different organs by damaging the interaction between pericytes and endothelial cells. In bone marrow, pericytes exert trophic functions on endothelial cells and haematopoietic cells through paracrine mechanisms. However, whether bone marrow pericytes are a target of diabetes-induced damage remains unknown. Here, we investigated whether type 2 diabetes can affect the abundance and function of bone marrow pericytes.

METHODS

We conducted an observational clinical study comparing the abundance and molecular/functional characteristics of CD146⁺ pericytes isolated from the bone marrow of 25 individuals without diabetes and 14 individuals with uncomplicated type 2 diabetes, referring to our Musculoskeletal Research Unit for hip reconstructive surgery.

RESULTS

Immunohistochemistry revealed that diabetes causes capillary rarefaction and compression of arteriole size in bone marrow, without changing CD146⁺ pericyte counts. These data were confirmed by flow cytometry on freshly isolated bone marrow cells. We then performed an extensive functional and molecular characterisation of immunosorted CD146⁺ pericytes. Type 2 diabetes caused a reduction in pericyte proliferation, viability, migration and capacity to support in vitro angiogenesis, while inducing apoptosis. AKT is a key regulator of the above functions and its phosphorylation state is reportedly reduced in the bone marrow endothelium of individuals with diabetes. Surprisingly, we could not find a difference in AKT phosphorylation (at either Ser473 or Thr308) in bone marrow pericytes from individuals with and without diabetes. Nonetheless, the angiocrine signalling reportedly associated with AKT was found to be significantly downregulated, with lower levels of fibroblast growth factor-2 (FGF2) and C-X-C motif chemokine ligand 12 (CXCL12), and activation of the angiogenesis inhibitor angiopoietin 2 (ANGPT2). Transfection with the adenoviral vector carrying the coding sequence for constitutively active myristoylated AKT rescued functional defects and angiocrine signalling in bone marrow pericytes from diabetic individuals. Furthermore, an ANGPT2 blocking antibody restored the capacity of pericytes to promote endothelial networking.

CONCLUSIONS/INTERPRETATION

This is the first demonstration of pericyte dysfunction in bone marrow of people with type 2 diabetes. An altered angiocrine signalling from pericytes may participate in bone marrow microvascular remodelling in individuals with diabetes.

Nonlocal Metasurfaces for Optical Signal Processing

Optical analog signal processing has been gaining significant attention as a way to overcome the speed and energy limitations of digital techniques. Metasurfaces offer a promising avenue towards this goal due to their efficient manipulation of optical signals over deeply subwavelength volumes. To date, metasurfaces have been proposed to transform signals in the spatial domain, e.g., for beam steering, focusing, or holography, for which angular-dependent responses, or nonlocality, are unwanted features that must be avoided or mitigated. Here, we show that the metasurface nonlocality can be engineered to enable signal manipulation in the momentum domain over an ultrathin platform. We explore nonlocal metasurfaces performing basic mathematical operations, paving the way towards fast and power-efficient ultrathin devices for edge detection and optical image processing.

A case of chronic asymptomatic central pontine myelinolysis with histological evidence of remyelination

Central pontine myelinolysis (CPM) is a neurological demyelinating disease of the pons. Although usually associated with rapid correction of hyponatremia, CPM may occur despite normonatremia, is often associated with chronic alcoholism and may be asymptomatic. Histological confirmation of asymptomatic CPM is rare. We describe an unusual post-mortem case of extensive but asymptomatic CPM in a chronic alcoholic patient with normonatremia. The affected part of the pons contained thinly myelinated axons with appearances supporting remyelination. We suggest that remyelination may account for the subclinical nature of this patient's CPM.

The adipokine leptin modulates adventitial pericyte functions by autocrine and paracrine signalling

Transplantation of adventitial pericytes (APCs) improves recovery from tissue ischemia in preclinical animal models by still unknown mechanisms. This study investigates the role of the adipokine leptin (LEP) in the regulation of human APC biological functions. Transcriptomic analysis of APCs showed components of the LEP signalling pathway are modulated by hypoxia. Kinetic studies indicate cultured APCs release high amounts of immunoreactive LEP following exposure to hypoxia, continuing upon return to normoxia. Secreted LEP activates an autocrine/paracrine loop through binding to the LEP receptor (LEPR) and induction of STAT3 phosphorylation. Titration studies using recombinant LEP and siRNA knockdown of LEP or LEPR demonstrate the adipokine exerts important regulatory roles in APC growth, survival, migration and promotion of endothelial network formation. Heterogeneity in LEP expression and secretion may influence the reparative proficiency of APC therapy. Accordingly, the levels of LEP secretion predict the microvascular outcome of APCs transplantation in a mouse limb ischemia model. Moreover, we found that the expression of the Lepr gene is upregulated on resident vascular cells from murine ischemic muscles, thus providing a permissive milieu to transplanted LEP-expressing APCs. Results highlight a new mechanism responsible for APC adaptation to hypoxia and instrumental to vascular repair.

The bone marrow pericyte: an orchestrator of vascular niche

The concept of pericyte has been changing over years. This cell type was believed to possess only a function of trophic support to endothelial cells and to maintain vasculature stabilization. In the last years, the discovery of multipotent ability of perivascular populations led to the concept of vessel/wall niche. Likewise, several perivascular populations have been identified in animal and human bone marrow. In this review, we provide an overview on bone marrow perivascular population, their cross-talk with other niche components, relationship with bone marrow stromal stem cells, and similarities and differences with the perivascular population of the vessel/wall niche. Finally, we focus on the regenerative potential of these cells and the forthcoming challenges related to their use as cell therapy products.