Biomimic Vein-Like Transparent Conducting Electrodes with Low Sheet Resistance and Metal Consumption

Abstract: In this contribution, inspired by the excellent resource management and material transport function of leaf veins, the electrical transport function of metallized leaf veins is mimicked from the material transport function of the vein networks. By electroless copper plating on real leaf vein networks with copper thickness of only several hundred nanometre up to several micrometre, certain leaf veins can be converted to transparent conductive electrodes with an ultralow sheet resistance 100 times lower than that of state-of-the-art indium tin oxide thin films, combined with a broadband optical transmission of above 80% in the UV–VIS–IR range. Additionally, the resource efficiency of the vein-like electrode is characterized by the small amount of material needed to build up the networks and the low copper consumption during metallization. In particular, the high current density transport capability of the electrode of > 6000 A cm−2 was demonstrated. These superior properties of the vein-like structures inspire the design of high-performance transparent conductive electrodes without using critical materials and may significantly reduce the Ag consumption down to < 10% of the current level for mass production of solar cells and will contribute greatly to the electrode for high power density concentrator solar cells, high power density Li-ion batteries, and supercapacitors.[Figure not available: see fulltext.]. © 2020, © 2020, The Author(s)

Copper Iodide on Spacer Fabrics as Textile Thermoelectric Device for Energy Generation

The integration of electronic functionalities into textiles for use as wearable sensors, energy harvesters, or coolers has become increasingly important in recent years. A special focus is on efficient thermoelectric materials. Copper iodide as a p-type thermoelectrically active, nontoxic material is attractive for energy harvesting and energy generation because of its transparency and possible high-power factor. The deposition of CuI on polyester spacer fabrics by wet chemical processes represents a great potential for use in textile industry for example as flexible thermoelectric energy generators in the leisure or industrial sector as well as in medical technologies. The deposited material on polyester yarn is investigated by electron microscopy, x-ray diffraction and by thermoelectric measurements. The Seebeck coefficient was observed between 112 and 153 µV/K in a temperature range between 30 °C and 90 °C. It is demonstrated that the maximum output power reached 99 nW at temperature difference of 65.5 K with respect to room temperature for a single textile element. However, several elements can be connected in series and the output power can be linear upscaled. Thus, CuI coated on 3D spacer fabrics can be attractive to fabricate thermoelectric devices especially in the lower temperature range for textile medical or leisure applications

Fabrication of self-assembled spherical Gold Particles by pulsed UV Laser Treatment

We report on the fabrication of spherical Au spheres by pulsed laser treatment using a KrF excimer laser (248 nm, 25 ns) under ambient conditions as a fast and high throughput fabrication technique. The presented experiments were realized using initial Au layers of 100 nm thickness deposited on optically transparent and low cost Borofloat glass or single-crystalline SrTiO3 substrates, respectively. High (111)-orientation and smoothness (RMS ≈ 1 nm) are the properties of the deposited Au layers before laser treatment. After laser treatment, spheres with size distribution ranging from hundreds of nanometers up to several micrometers were produced. Single-particle scattering spectra with distinct plasmonic resonance peaks are presented to reveal the critical role of optimal irradiation parameters in the process of laser induced particle self-assembly. The variation of irradiation parameters like fluence and number of laser pulses influences the melting, dewetting and solidification process of the Au layers and thus the formation of extremely well shaped spherical particles. The gold layers on Borofloat glass and SrTiO3 are found to show a slightly different behavior under laser treatment. We also discuss the effect of substrates.We report on the fabrication of spherical Au spheres by pulsed laser treatment using a KrF excimer laser (248 nm, 25 ns) under ambient conditions as a fast and high throughput fabrication technique. The presented experiments were realized using initial Au layers of 100 nm thickness deposited on optically transparent and low cost Borofloat glass or single-crystalline SrTiO3 substrates, respectively. High (111)-orientation and smoothness (RMS ≈ 1 nm) are the properties of the deposited Au layers before laser treatment. After laser treatment, spheres with size distribution ranging from hundreds of nanometers up to several micrometers were produced. Single-particle scattering spectra with distinct plasmonic resonance peaks are presented to reveal the critical role of optimal irradiation parameters in the process of laser induced particle self-assembly. The variation of irradiation parameters like fluence and number of laser pulses influences the melting, dewetting and solidification process of the Au layers and thus the formation of extremely well shaped spherical particles. The gold layers on Borofloat glass and SrTiO3 are found to show a slightly different behavior under laser treatment. We also discuss the effect of substrates

Self-Assembled Graphene/MWCNT Bilayers as Platinum- Free Counter Electrode in Dye-Sensitized Solar Cells

We describe the preparation and properties of bilayers of graphene- and multi-walled carbon nanotubes (MWCNTs) as an alternative to conventionally used platinum-based counter electrode for dye-sensitized solar cells (DSSC). The counter electrodes were prepared by a simple and easy-to-implement double self-assembly process. The preparation allows for controlling the surface roughness of electrode in a layer-by-layer deposition. Annealing under N2 atmosphere improves the electrode's conductivity and the catalytic activity of graphene and MWCNTs to reduce the I3 − species within the electrolyte of the DSSC. The performance of different counter-electrodes is compared for ZnO photoanode-based DSSCs. Bilayer electrodes show higher power conversion efficiencies than monolayer graphene electrodes or monolayer MWCNTs electrodes. The bilayer graphene (bottom)/MWCNTs (top) counter electrode-based DSSC exhibits a maximum power conversion efficiency of 4.1 % exceeding the efficiency of a reference DSSC with a thin film platinum counter electrode (efficiency of 3.4 %). In addition, the double self-assembled counter electrodes are mechanically stable, which enables their recycling for DSSCs fabrication without significant loss of the solar cell performance. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Multicrystalline silicon thin-film solar cells based on vanadium oxide heterojunction and laser-doped contacts

This is the peer reviewed version of the following article: Martín, I., López, G., Plentz, J., Jin, C., Ortega, P., Voz, C., Puigdollers, J., Gawlik, A., Jia, G. and Andrä, G. (2019), Multicrystalline Silicon Thin‐Film Solar Cells Based on Vanadium Oxide Heterojunction and Laser‐Doped Contacts. Phys. Status Solidi A, 216: 1900393, which has been published in final form at https://doi.org/10.1002/pssa.201900393. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Liquid phase crystallized (LPC) silicon thin films on glass substrates are a feasible alternative to conventional crystalline silicon (c-Si) wafers for solar cells. Due to substrate limitation, a low-temperature technology is needed for solar cell fabrication. While silicon heterojunction is typically used, herein, the combination of vanadium oxide/c-Si heterojunction as emitter and base contacts defined by IR laser processing of phosphorus-doped amorphous silicon carbide stacks is explored. LPC solar cells are fabricated using such technologies to identify their issues and advantages with a promising performance of an active-area efficiency of 5.6%. Apart from the absence of light-trapping techniques, the relatively low efficiency obtained is attributed to a low lifetime in the LPC silicon bulk. These poor material properties imply a short diffusion length that makes it that only photogenerated carriers in the emitter regions can be collected. Consequently, future devices should show narrower base contact regions, suggesting a shorter-wavelength laser, combined with longer LPC substrate lifetimes.Peer ReviewedPostprint (author's final draft

Nanopatterned indium tin oxide as a selective coating for solar thermal applications

Indium tin oxide (ITO) coatings have been proposed to reduce thermal emission losses for solar thermal applications. Unfortunately, ITO also has a large amount of free charge carriers (∼1 × 1020 per cm3), which absorb sunlight. To address this issue, we propose a nano-patterned ITO-coated quartz exhibiting both anti-reflectivity (to maximize solar transmission) and low emissivity (to minimize long wavelengths radiative losses). A record small-size nanosphere (∼60 nm) etch mask was prepared via double self-assembly, followed by dry etching and characterisation. In parallel, alternative nanopattern geometries were modelled using the Lumerical FDTD software to optimise short wavelength transmission without diminishing the inherently low emissivity of unetched ITO. It was found that an inverted moth's eye pattern (height = 250 nm and spacing = 80 nm) gave the best results at various solar concentrations (1 sun @ 100 °C, 10 suns @ 400 °C, and 100 suns @ 600 °C), resulting in ∼7% improvement in the solar weighted transmission as well as a similar boost in the overall efficiency factor for selectivity. It was concluded that if the proposed deposition/etching processes can be cost-effectively scaled in a continuous process, it would provide a net performance boost for most solar thermal technologies

Assessment of the reliability and quality of breast cancer related videos on TikTok and Bilibili: cross-sectional study in China

BackgroundAs the most common malignant tumor in the world, breast cancer also brings a huge disease burden to China. Ordinary people are increasingly inclined to use the Internet, especially video social platforms, as a source of health information. Educating the public to obtain correct information is important to reduce the incidence of breast cancer and improve the prognosis. However, the quality and reliability of breast cancer-related video content have not been fully studied.ObjectiveThis study aims to evaluate the quality of the information of breast cancer-related videos on TikTok and Bilibili video sharing platforms and factors related to video quality.MethodsWe collected the top 100 videos about breast cancer on TikTok and Bilibili, respectively. Categorize videos according to video source and video content. Video quality and reliability were assessed using Global Quality Score (GQS) and modified DISCERN (mDISCERN) tools. We also analyzed the correlation between video quality and video likes, comments, saves, and shares.ResultsAlthough the quality and reliability of Bilibili’s breast cancer videos were higher than TikTok (p = 0.002 and p = 0.001, respectively), the video quality of both video sharing platforms was not satisfactory, with a median GQS scores of 2.00 and 3.00 and mDISCERN scores of 1.00 and 2.00, respectively. In general, the quality and reliability of videos released by medical practitioners were higher than those of non-medical practitioners, and the quality and reliability of videos covering disease-related knowledge were higher than those of news reports (all p &lt; 0.001). Among medical practitioners, the quality of videos uploaded by doctors in breast disease was significantly lower than that of doctors in other areas (p &lt; 0.05). There was a significant positive correlation between video quality and duration (r = 0.240, p &lt; 0.001), a weak negative correlation between video quality and likes (r = 0.191, p &lt; 0.01), video quality and comments (r = 0.256, p &lt; 0.001), video reliability and likes (r = 0.198, p &lt; 0.001), video reliability and comments (r = 0.243, p &lt; 0.01).ConclusionOur study shows that the quality and reliability of breast cancer-related videos on TikTok and Bilibili are poor, and the overall quality is unsatisfactory. But videos uploaded by medical practitioners covering disease knowledge, prevention and treatment are of higher quality. Medical practitioners are encouraged to publish more high-quality videos, while video social platforms should formulate relevant policies to censor and supervise health education videos, so as to enable the public to obtain reliable health information

Charakterisierung der elektrischen und optischen Eigenschaften von Silizium-basierten Materialien

In this work, the electrical and luminescence properties of a series of Si based materials used for photovoltaics, microelectronics and nanoelectronics have been investigated by means of electron beam induced current (EBIC), cathodoluminescence (CL), photoluminescence (PL) and electroluminescence (EL). Photovoltaic Si produced by block casting has been investigated by EBIC on wafers sliced from different parts of the ingot. The impact of selected solar cell processing steps on the material properties has been evaluated by EBIC utilizing adjacent wafers from the ingot. The temperature dependence of dislocations’ EBIC contrast was measured to assess the degree of dislocation contamination with impurities, yielding low dislocation contamination for the middle of the block and high contamination in the top and bottom regions. This is in agreement with the impurity distribution in the block. It was found that phosphorus diffusion gettering (PDG) followed by SiN firing greatly reduces the recombination activity of extended defects at room temperature, and improves the bulk property simultaneously. The improvement is attributed to both PDG of metal impurities and a passivation effect of SiN firing. In order to better understand the factors limiting the properties of thin polycrystalline Si layers prepared by the Aluminum induced layer exchange (Alile) technique, epilayers grown on (111) and (100) monocrystalline Si substrates were used as a model system to investigate the impact of processing temperature (Ts) and type of substrate. It was found that no dislocations are formed for epilayers on (100) Si, while a high density of dislocations was detected on epilayers prepared on (111) Si at 450 °C. The dislocation density decreases with increasing TS. The diffusion lengths extracted from the energy dependent EBIC collection efficiencies reveal an improvement of the epilayer quality with increasing TS during growth from 450 °C to 650 °C, and a decrease of the epilayer quality at 700 °C. This is attributed to a reduction of the dislocation density with increasing TS and a formation of precipitates during the process. Precipitate formation of at 700 °C is limited because the metal impurities are very mobile at high TS, resulting in a homogeneous distribution of the impurities. Because the impurities are effective lifetime killers of the minority carriers, so the diffusion length decreases. PL measurements on epilayers grown on Si substrates revealed no characteristic dislocation-related luminescence (DRL) lines at room temperature and 77 K, while intense characteristic DRL lines D1 - D4 have been detected in the sample prepared by the Alile technique. This indicates that dislocations in the Alile sample are relatively clean. The possible reason for the purification of the Alile samples is Al induced gettering during the polycrystalline Si layer growth. The diffusion length in the thin top layer of Si-on-insulator (SOI) samples has been successfully measured by EBIC employing suppression of the surface recombination at the buried oxide layer and at surface of the top layer by biasing. The measured diffusion length is several times larger than the layer thickness. Dislocation networks produced by Si wafer direct bonding have been investigated with regard to their electrical properties by EBIC. The networks were observed to show charge carrier collection and electrical conduction. Inhomogeneities in the charge collection were detected in n- and p-type samples under appropriate beam energy. The EBIC contrast behavior can be understood under the consideration of the positively charged oxide precipitates along with dislocations charged with majority carriers, where the appearance of the contrast in dark or bright depends strongly on the ratio of the collection and the recombination loss of the carriers.The luminescence properties of Si nanostructures (Si nanowires, Si nano rods, porous Si, and Si/SiO2 multi quantum wells (MQWs)) are another important subject of this work. Sub-bandgap infrared (IR) luminescence around 1570 nm has been found in Si nanowires, nano rods and porous Si. PL measurements with samples immersed in different liquid media, for example, in aqueous HF (50%), concentrated H2SO4 (98%) and H2O2 established that the sub-bandgap IR luminescence originates from the Si/SiOx interface. Its origin was explained in terms of a simple recombination model through radiative interface states. EL in the sub-bandgap IR range has been observed in simple diodes prepared on porous Si and MQWs at room temperature. The results show the possibility to fabricate an efficient light emitter around 1570 nm wavelength based on the radiative recombination at the Si/Si oxide interface. Based on the knowledge about radiative transitions via the interface states, an improved understanding of luminescence in dislocated samples was proposed.In der vorliegenden Arbeit werden die elektrischen und Lumineszenzeigenschaften von verschiedenen Si-basierten Materialien mit Hilfe von Elektronenstrahlinduziertem Strom (EBIC), Kathodolumineszenz (CL), Photolumineszenz (PL) und Elektrolumineszenz (EL) untersucht. Die elektrischen Eigenschaften von Blockguss-Solar-Si wurden mittels EBIC an Proben aus verschiedenen Blockhöhen untersucht. Durch EBIC-Messungen an Parallelproben, die im Block unmittelbar benachbart waren, aber unterschiedlichen thermischen Prozessen unterzogen wurden, konnte die Wirkung ausgewählter Prozessschritte auf die Materialeigenschaften verfolgt werden. Aus den gemessenen Temperaturabhängigkeiten des EBIC-Kontrastes der Versetzungen lässt sich ableiten, dass in der Mitte des Blockes die Kontamination der Versetzungen mit metallischen Verunreinigungen gering ist, am Boden und in der Kappe aber deutlich höher. Das ist in guter Übereinstimmung mit der Höhnenverteilung der Verunreinigungen im Block. Es wurde festgestellt, dass Phosphordiffusionsgetterung (PDG) mit anschließendem Feuern einer aufgebrachten SiN-Schicht die Rekombinationsaktivität der ausgedehnten Defekten bei Raumtemperatur deutlich reduziert und gleichzeitig die Volumenqualität verbessert. Die Verbesserung wird auf Getterung von metallischen Verunreinigungen infolge PDG und die Passivierungswirkung des SiN-Feuerns zurückführt. Um die Faktoren, die die Eigenschaften dünner polykristalliner, mittels sogenannter Al-induzierter Schichtaustauschtechnik (Alile) hergestellter Si-Schichten besser verstehen zu können, wurden als Modellsystem für die Untersuchung des Einflusses von Substrate und Prozesstemperatur Epischichten auf (111)- und (100)-orientierten einkristallinem Si abgeschieden. Es wurde festgestellt, das Epischichten auf (100) Si versetzungsfrei wachsen nachgewiesen hat, während Epischichten auf (111) Si eine hohe Versetzungendichte bei 450 °C aufweisen. Die Dichte der Verstzungen nimmt mit steigender Substrattemperatur (TS) ab. Die aus der energienabhängigen Messungen der EBIC-Sammlungseffizienz ermittelten Diffusionslängen zeigen für (111) Si eine Zunahme der Schichtqualität mit steigender TS bis 650 °C, und einen Abfall für 700 °C. Das Abfallen der Diffusionslänge bei 700 °C deutet daraufhin, dass die Ausscheidungsbildung nicht effektiv ist und sich die Verunreinigungen fast gleichmäßig in der Schicht verteilen. Da die Verunreinigungen aktive Rekombinationszentren und Lebensdauerkiller für Minoritätsladungsträger sind, nimmt so die Diffusionslänge ab. PL-Messungen an auf (100)- und (111)-Si gewachsenen Epischichten haben keine versetzunginduzierte Lumineszenz (DRL) D1-D4 nachgewiesen. In der Alile-Probe tritt dagegen ein intensives DRL-Siganl auf. Dies bedeutet, dass die Versetzungen in der Alile-Probe relativ sauber sind, was wahrscheinlich auf eine Al-induzierte Getterung von Verunreinigungen zurückzuführen ist. Die Diffusionslänge in der dünnen oberen Schicht von SOI-Proben wurde erfolgreich mittels EBIC gemessen, indem die Oberflächenrekombination an der Oberfläche und an der vergrabenen Oxidschicht mit Hilfe angelegter Spannungen unterdrückt wurde. Die gemessene effektive Diffusionslänge ist mehrfach länger als der Schichtdicke. Durch direktes Bonden von Si-Wafern hergestellte Versetzungsnetzwerke wurden mit EBIC hinsichtlich ihrer elektrischen Eigenschaften untersucht. Es wurde beobachtet, dass die Netzwerke Ladungssammlung und elektrische Leitung zeigen. Bei bestimmten Strahlenergien wurden Inhomogenitäten der Ladungssammlung nachgewiesen. Das Verhalten des EBIC-Kontrastes dieser Inhomogenitäten kann unter der Berücksichtigung der positiv geladenen Sauerstoffausscheidungen im Netzwerk und der mit Majoritätsträgern beladenen Versetzungen verstanden werden. Das Auftreten von Dunkel- oder Hellkontrast hängt stark vom Verhältnis zwischen Ladungssammlung und Rekombinationverlust am Netzwerk ab. Die Lumineszenzeigenschaften von Si-Nanostrukturen (Si-Nanodrähte, Nanostäbe, poröses Si und Si/SiO2 Multi-Quantentöpfe (MQW)) sind ein anderes wichtiges Thema der Arbeit. Ein infrarotes Lumineszenzband im „sub-bandgap“-Bereich wurde in Si-Nanodrähten, Nanostäben und porösem Si entdeckt. PL-Messungen in flüssigen Medien wie HF (50%), H2SO4 (98%) und H2O2 ergaben, dass das Lumineszenzband von der Si/SiOx-Grenzfläche stammt. Zur Erklärung dieses Bandes wurde ein einfaches Rekombinationsmodel via Grenzflächenzustände vorgeschlagen. EL-Messungen an Dioden aus porösem Si und MQW zeigten infrarote Lumineszenz im „sub-bandgap“-Bereich bei 300 K. Die Ergebnisse demonstrieren die Möglichkeit, einen effizienten Lichtemitter bei 1570 nm Wellenlänge auf der Basis strahlender Rekombination an der Si/SiOx-Grenzfläche herzustellen. Basierend auf dem Wissen über strahlende Rekombination an der Si/SiOx-Grenzfläche, wurde ein modifiziertes Verständnis der Lumineszenz in versetztem Si vorgeschlagen

Low temperature chemical treatment of graphene films made by double self-assembly process to improve sheet resistance

In this study, a low temperature hydro iodic acid (HI) vapor treatment of the self-assembled graphene films has been developed, and the electrical, optical, structural and morphological properties were investigated by four point probe, UV-Visible spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM). Mono-, doubleand triple-layer of graphene flakes were deposited on glass substrates by using the Double Self-Assembly (DSA) process. The self-assembled graphene films were treated with HI vapors at 40 degrees C for different time intervals between 1 and 24 h. In addition, graphene deposition and HI-vapor treatment (at 40 degrees C for 1 h) was enforced three times to the same substrate. The optical transparency values of the self-assembled mono- (MGFs), double- (DGFs) and triple-layer graphene flakes (TGFs) were measured as 91, 85 and 80%, respectively (values at 550 nm). Due to the HI-vapor treatment, the sheet resistance of MGFs significantly reduced from 1.1 x 10(7) Omega omega square(-1) to 2.9 x 10(4) omega square(-1), the transparency of the graphene films slightly reduced by 2-5%, the I-D/I-G ratio of the DGFs decreased from 1.01 to 0.81, while the I-2D/I-G ratio increased from 0.43 to 0.48 in the Raman spectrum. Thanks to its impressive reducing effect on sheet resistance, HI-vapor treatment can be a suitable method to improve the conductivity of low-cost large area graphene films

Wet chemical method for highly flexible and conductive fabrics for smart textile applications

This study reports the preparation of highly flexible and conductive fabrics containing zinc oxide (ZnO), silver nanowires (AgNW) and graphene flakes (GFs) by simple vacuum filtration. The ZnO particles prepared with sol-gel method in large sizes with flower-like shape were used as filler and became the first layer to be coated on the fabric surface. These particles covered the gaps at the junction of the fabric fibers, providing a suitable area for the deposition of subsequent layers of AgNW and GFs. The structural, morphological and conductivity properties of the prepared conductive fabric were investigated by XRD, optical and electron microscopy as well as four-point probe conductivity measurement. The optical images showed that a continuous conductive network was obtained that allowed electron transport across the fabric surface. The fabric was found to have a remarkably low sheet resistance of an average of 1.5 Ω/sq. This result displays that promising candidates suitable for conductive textile applications can be prepared by simple vacuum filtration method