Improved Cleaning Process for Textured ∼25 μm Flexible Mono-Crystalline Silicon Heterojunction Solar Cells with Metal Backing

An improved cleaning process is developed to remove front surface contamination for single heterojunction solar cells on textured surfaces on ∼25 μm thick exfoliated, flexible mono-crystalline silicon. The process is very effective in cleaning metallic and organic residues, without introducing additional contamination or degrading the supporting back metal used for ultrathin substrate handling. Quantitative analysis of the Auger electron spectra shows significant potassium contamination reduction (∼0.89% atomic) using the new cleaning process. An open-circuit voltage enhancement of 22 mV and an absolute 1.5% increase in conversion efficiency are observed with the new cleaning procedure for the exfoliated thin solar cells. Thin crystalline silicon (c-Si) solar cells are of much interest due to their potential to achieve high efficiency and reduce cost by using less Si material. However, there are significant challenges to commercialize sub-100 μm thin Si substrates as they can easily break or crack with wafer-handling, resulting in low yield in a solar cell manufacturing line. We have introduced in our earlier work, 1 a kerf-less process in which ultra-thin (∼25 μm) and flexible mono-crystalline Si substrates can be obtained through an exfoliation technique from a thicker (>450 μm) parent wafer. These substrates, when exfoliated, have thick (∼50 μm) electroplated nickel (Ni) metal backing, which provides mechanical support to the thin Si and enables ease of processing for semiconductor device fabrication. Previously we have demonstrated single heterojunction (SHJ) solar cells fabricated on this type of substrate exhibiting efficiencies 14.9% on as-exfoliated substrates. 2 However, on textured surfaces efficiency was limited to 11%. We postulated that one of the issues that could be limiting the performance of the cells is unintentional front surface contamination introduced during wet chemical processes before hydrogenated amorphous Si (a-Si:H) deposition of the front surface emitter, which can limit the open-circuit voltage (V OC ) of these solar cells. This could happen due to the presence of potassium ions introduced from potassium hydroxide (KOH) during texturing. For decontamination we could not use SC-2 solution (5:1:1 ratio of H 2 O, H 2 O 2 , HCl at 80 o C) as it reacts rather aggressively with the electroplated Ni back metal. Instead, we used a piranha solution (1:1 ratio of H 2 O 2 , H 2 SO 4 ) for both decontamination from potassium ions and removal of organic contaminants, which did not seem to show corrosion degradation in the back side Ni. The pH level of HCl is slightly lower compared to H 2 SO 4, and SC-2 solution has a stronger effervescent action than piranha solution. This may explain why the Ni is much more affected by the SC-2 clean compared to the piranha clean. Nevertheless, piranha-treatment alone is probably inadequate for metal residues or potassium related contaminant removal after texturing. In this work, we attempted to address the front surface contamination issue by developing an improved cleaning procedure for textured silicon surfaces for mono-crystalline exfoliated Si substrate. We assumed the cleaning process employed for the rear surface is sufficient as it was done using traditional RCA cleaning 3 on a textured thick parent wafer. With the help of X-ray Photoelectron Spectroscopy (XPS) we have identified the chemical bonding nature of key contaminants at the surface i.e. carbon and potassium. We have also employed Auger electron spectroscopy (AES) to quantify the atomic concentration of the impurities before and after implementation of various wet chemical cleans. We have fabricated and characterized SHJ solar cells on z E-mail: [email protected] both exfoliated and bulk (∼180 μm) substrates to study the effect of contamination on device performance and how an improved surface clean procedure can affect the solar cell efficiency. Experimental A detailed process flow for the exfoliation process is discussed in previous work. 2 Sample 3 was treated with a 1:40 water based solution of SC-15 5 (Surface Chemistry Discoveries, Inc.) at 40 o C for 5 minutes. SC-15 is used as an alternative to RCA clean. It is well documented in the literature 6,7 that SC-1 step (5:1:1 ratio of H 2 O, H 2 O 2 , NH 4 OH at 80 o C) in RCA cleans causes micro-roughening and even pitting of silicon substrates, thereby introducing trap states (D it ) at the heterointerface. 8 We ensure extremely low anisotropic silicon etch rate to reduce roughening the surface by using high dilution (1:40) of SC-15 formulation. This is verified by scanning electron microscopy (SEM) done before and after SC-15 treatment. The surface morphology doesn't change as the solution was not concentrated enough and the temperature wasn't high enough to round off the peaks of the random pyramids that has been typically shown in previous literature 11,12 The chelating agent was used to increase the capacity of the cleaning bath to retain metals in solution by acting as a multi-dentate ligand forming a stable multi-dentate complex with the metal cations, which enhances the dissolution of metallic residues on the silicon surface. 13,14 The temperature of 40 o C aids in the contaminant removal, but is still not high enough to result in anisotropic etching of the silicon. Finally, sample 4 was treate

Patterns of antibiotic use, pathogens, and prediction of mortality in hospitalized neonates and young infants with sepsis: A global neonatal sepsis observational cohort study (NeoOBS)

BACKGROUND: There is limited data on antibiotic treatment in hospitalized neonates in low- and middle-income countries (LMICs). We aimed to describe patterns of antibiotic use, pathogens, and clinical outcomes, and to develop a severity score predicting mortality in neonatal sepsis to inform future clinical trial design. METHODS AND FINDINGS: Hospitalized infants <60 days with clinical sepsis were enrolled during 2018 to 2020 by 19 sites in 11 countries (mainly Asia and Africa). Prospective daily observational data was collected on clinical signs, supportive care, antibiotic treatment, microbiology, and 28-day mortality. Two prediction models were developed for (1) 28-day mortality from baseline variables (baseline NeoSep Severity Score); and (2) daily risk of death on IV antibiotics from daily updated assessments (NeoSep Recovery Score). Multivariable Cox regression models included a randomly selected 85% of infants, with 15% for validation. A total of 3,204 infants were enrolled, with median birth weight of 2,500 g (IQR 1,400 to 3,000) and postnatal age of 5 days (IQR 1 to 15). 206 different empiric antibiotic combinations were started in 3,141 infants, which were structured into 5 groups based on the World Health Organization (WHO) AWaRe classification. Approximately 25.9% (n = 814) of infants started WHO first line regimens (Group 1-Access) and 13.8% (n = 432) started WHO second-line cephalosporins (cefotaxime/ceftriaxone) (Group 2-"Low" Watch). The largest group (34.0%, n = 1,068) started a regimen providing partial extended-spectrum beta-lactamase (ESBL)/pseudomonal coverage (piperacillin-tazobactam, ceftazidime, or fluoroquinolone-based) (Group 3-"Medium" Watch), 18.0% (n = 566) started a carbapenem (Group 4-"High" Watch), and 1.8% (n = 57) a Reserve antibiotic (Group 5, largely colistin-based), and 728/2,880 (25.3%) of initial regimens in Groups 1 to 4 were escalated, mainly to carbapenems, usually for clinical deterioration (n = 480; 65.9%). A total of 564/3,195 infants (17.7%) were blood culture pathogen positive, of whom 62.9% (n = 355) had a gram-negative organism, predominantly Klebsiella pneumoniae (n = 132) or Acinetobacter spp. (n = 72). Both were commonly resistant to WHO-recommended regimens and to carbapenems in 43 (32.6%) and 50 (71.4%) of cases, respectively. MRSA accounted for 33 (61.1%) of 54 Staphylococcus aureus isolates. Overall, 350/3,204 infants died (11.3%; 95% CI 10.2% to 12.5%), 17.7% if blood cultures were positive for pathogens (95% CI 14.7% to 21.1%, n = 99/564). A baseline NeoSep Severity Score had a C-index of 0.76 (0.69 to 0.82) in the validation sample, with mortality of 1.6% (3/189; 95% CI: 0.5% to 4.6%), 11.0% (27/245; 7.7% to 15.6%), and 27.3% (12/44; 16.3% to 41.8%) in low (score 0 to 4), medium (5 to 8), and high (9 to 16) risk groups, respectively, with similar performance across subgroups. A related NeoSep Recovery Score had an area under the receiver operating curve for predicting death the next day between 0.8 and 0.9 over the first week. There was significant variation in outcomes between sites and external validation would strengthen score applicability. CONCLUSION: Antibiotic regimens used in neonatal sepsis commonly diverge from WHO guidelines, and trials of novel empiric regimens are urgently needed in the context of increasing antimicrobial resistance (AMR). The baseline NeoSep Severity Score identifies high mortality risk criteria for trial entry, while the NeoSep Recovery Score can help guide decisions on regimen change. NeoOBS data informed the NeoSep1 antibiotic trial (ISRCTN48721236), which aims to identify novel first- and second-line empiric antibiotic regimens for neonatal sepsis. TRIAL REGISTRATION: ClinicalTrials.gov, (NCT03721302)

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Breast cancer management pathways during the COVID-19 pandemic: outcomes from the UK ‘Alert Level 4’ phase of the B-MaP-C study

Abstract: Background: The B-MaP-C study aimed to determine alterations to breast cancer (BC) management during the peak transmission period of the UK COVID-19 pandemic and the potential impact of these treatment decisions. Methods: This was a national cohort study of patients with early BC undergoing multidisciplinary team (MDT)-guided treatment recommendations during the pandemic, designated ‘standard’ or ‘COVID-altered’, in the preoperative, operative and post-operative setting. Findings: Of 3776 patients (from 64 UK units) in the study, 2246 (59%) had ‘COVID-altered’ management. ‘Bridging’ endocrine therapy was used (n = 951) where theatre capacity was reduced. There was increasing access to COVID-19 low-risk theatres during the study period (59%). In line with national guidance, immediate breast reconstruction was avoided (n = 299). Where adjuvant chemotherapy was omitted (n = 81), the median benefit was only 3% (IQR 2–9%) using ‘NHS Predict’. There was the rapid adoption of new evidence-based hypofractionated radiotherapy (n = 781, from 46 units). Only 14 patients (1%) tested positive for SARS-CoV-2 during their treatment journey. Conclusions: The majority of ‘COVID-altered’ management decisions were largely in line with pre-COVID evidence-based guidelines, implying that breast cancer survival outcomes are unlikely to be negatively impacted by the pandemic. However, in this study, the potential impact of delays to BC presentation or diagnosis remains unknown

Bio-Monitoring of Airborne Fungi and Antifungal Activity of Clerodendrum Infortanum L. Against Dominant Fungi

The present study provides baseline information on the quantitative and qualitative estimation of aeromycoflora. Burkard personal airsampler and Anderson two stage airsampler were used to detect the quantitative and qualitative estimation of aeromycoflora. 17 non-viable fungal spores were recorded with the aid of Burkard personal airsampler and 12 viable fungal genera were detected using Anderson two stage airsampler. Higher concentration airborne fungi observed in the month of March. Aspergillus sp, Ascospore, Basidiospore, Curvularia sp, Alternaria sp were found to be Nigrospora sp most predominant nonviable fungal genera whereas dominant viable genera were Aspergillus sp, Penicillium sp, Cladosporium sp, Curvularia sp, Trichoderma sp and Fusarium sp in both the environments. The result of antifungal potential of Clerodendrum infortunatum showed highest efficacy against Aspergillus sp followed by Penicillium sp and Fusarium sp. This present study provided the baseline information about the viable and non-viable concentration in the study sites. Besides the outcomes of this study along with the insightful explanation could aptly provide basis for strategizing effective preventive measures against airborne-fungi. Those are responsible for causing different agricultural crops diseases and human respiratory ailments

Boosting thermoelectric power factor of free-standing Poly (3,4ethylenedioxythiophene):polystyrenesulphonate films by incorporation of bismuth antimony telluride nanostructures

We demonstrate that introduction of p-type Bi0.5Sb1.5Te3 nanostructures into the polymer matrix not only causes highly adherent drop-casted films of PEDOT:PSS (on Kapton sheets) to attain a free-standing nature but also brings a significant improvement in their thermoelectric properties. Hall and ESR measurements of these hybrid films clearly show that both the carrier concentration and mobility can be varied with Bi0.5Sb1.5Te3 content. Whereas, results of X-ray diffraction, Raman and X-ray photoelectron spectroscopy confirm the enhancement in chain alignment and better connectivity among PEDOT:PSS and Bi0.5Sb1.5Te3 nanosheets; leading to remarkable enhancement of electrical conductivity. These hybrid films, due to energy filtering of charge carriers at the organic/inorganic interface, exhibit improvement in the Seebeck coefficient also. In fact, such a synergetic combination of improved electrical conductivity and Seebeck coefficient expertly tailors the power factor (from order of similar to 10(-4) to 8.3 mu W/mK(2)) over a vast range. The optimized films are tested for their power conversion ability and a single thermoelement based device exhibits an open circuit voltage similar to 536 mu V and current similar to 134 mu A for a temperature difference of 53 degrees C. Such an evolution of organic-inorganic hybrid films in a flexible, free-standing motif with enhanced thermoelectric properties exhibit good potential for recovering heat from the curved hot surfaces