Mask and plate: a scalable front metallization with low-cost potential for III-V-based tandem solar cells enabling 31.6 % conversion efficiency.

Low-cost approaches for mass production of III-V-based photovoltaics are highly desired today. For the first time, this work presents industrially relevant mask and plate for front metallization of III-V-based solar cells replacing expensive photolithography. Metal contacts are fabricated by nickel (Ni) electroplating directly onto the solar cell's front using a precisely structured mask. Inkjet printing offers low-cost and high-precision processing for application of an appropriate plating resist. It covers the solar cell's front side with narrow openings for subsequent electroplating. The width of the resulting Ni contacts is as low as (10.5 ± 0.8) µm with sharp edges and homogenous shape. The 4 cm2-sized champion III-V-on-silicon triple-junction solar cell with mask and plate front metallization reaches a certified conversion efficiency η of (31.6 ± 1.1) % (AM1.5 g spectrum). It performs just as well as the reference sample with photolithography-structured evaporated front contacts, which reaches η = (31.4 ± 1.1) %.

Screen Printable Sol-Gel Materials for High-Throughput Borosilicate Glass Film Production.

The use of sol-gel materials can simplify the industrial fabrication of high-efficiency silicon solar cells if a suitable deposition method is established. In this work, we investigate the possibilities to adapt a borosilicate glass sol-gel to provide a stable screen printing process. This material has previously been used as a boron dopant source for silicon solar cells. We now use an adjusted synthesis process, with an increased gelling time and different additives. This changes the rheological properties (i.e., the elastic and viscous moduli G' and G″) in a way that avoids the dripping of paste through the screen and that stabilizes the material transfer in subsequent printing steps. Using this synthesis process, we were able to show a printing process with long-term stability of more than 500 prints. When comparing the adjusted to the initial paste, we show that, after thermal treatment, the obtained thin films are very similar in terms of their constitution, with a refractive index between n = 1.47 (initial) and n = 1.55 (adjusted). We also show that they provide the same amount of doping under the tested conditions (950 °C, 30 min), resulting in sheet resistances of R□ = (42.5 ± 2.6) Ω/□ (initial) and R□ = (46.4 ± 3.6) Ω/□ (adjusted).

Filament stretching during micro-extrusion of silver pastes enables an improved fine-line silicon solar cell metallization.

The metallization of heterojunction solar cells requires a further reduction of silver consumption to lower production costs and save resources. This article presents how filament stretching of polymer-based low-temperature curing Ag pastes during micro-extrusion enables this reduction while at the same time offering a high production throughput potential. In a series of experiments the relationship between the printing velocity and the filament stretching, thus the reduction of Ag-electrode widths and Ag laydown is evaluated. Furthermore, an existing filament stretching model for the parallel dispensing process is advanced further and utilized to calculate the elongational viscosity. The stretching effect enables a reduction of the Ag-electrode width by down to Δwf = - 40%rel. depending on the nozzle diameter and paste type. The Ag laydown has been reduced from mAg,cal. = 0.84 mg per printed line to only mAg,cal. = 0.54 mg per printed Ag-electrode when 30 µm nozzle openings are used, demonstrating the promising potential of parallel dispensing technology for the metallization of silicon heterojunction solar cells.

A model for screen utility to predict the future of printed solar cell metallization.

Fine line screen printing for solar cell metallization is one of the most critical steps in the entire production chain of solar cells, facing the challenge of providing a conductive grid with a minimum amount of resource consumption at an ever increasing demand for higher production speeds. The continuous effort of the industrial and scientific community has led to tremendous progress over the last 20 years, demonstrating an average reduction rate for the finger width of approximately 7 µm per year with the latest highlight of achieving widths of 19 µm. However, further reductions will become a major challenge because commonly used metal pastes are not able to penetrate arbitrary small screen opening structures. Therefore, this study introduces the novel dimensionless parameter screen utility index SUI which quantifies the expected printability of any 2-dimensional screen architecture in reference to a given paste. Further, we present a full theoretical derivation of the SUI, a correlation to experimental results and an in-depth simulation over a broad range of screen manufacturing parameters. The analysis of the SUI predicts the point when commonly used wire materials will fail to provide sufficient meshes for future solar cell metallization tasks. Therefore, novel wire materials (e.g. the use of carbon nanotubes) with very high ultimate tensile strengths are discussed and suggested in order to fulfill the SUI requirements for printing contact fingers with widths below 10 µm. We further analyze economic aspects of design choices for screen angles by presenting an analytical solution for the calculation of mesh cutting losses in industrial screen production. Finally, we combine all aspects by presenting a generalized approach for designing a 2-dimensional screen architecture which fulfills the task of printing at a desired finger width.

Hypoglycemia While Driving in Insulin-Treated Patients: Incidence and Risk Factors.

OBJECTIVES: This study aimed to investigate a potential daily-life concern for patients with diabetes hypoglycemia while driving by (1) estimating their incidence in insulin-treated drivers, (2) determining factors associated with their occurrence, and (3) analyzing patients' behavior regarding prevention of hypoglycemia. METHODS: We conducted an observational study from November 2013 to May 2018 in the endocrinology-diabetology-nutrition department of our university hospital. All patients treated for diabetes older than 18 years admitted in the department were eligible. A specific questionnaire assessing attitudes, knowledge, and consequences of hypoglycemia was provided. In this study, only insulin-treated patients who regularly drive were analyzed. RESULTS: On the 233 insulin-treated drivers included, 45 (19%) self-reported at least 1 hypoglycemia while driving in the preceding year. Two factors were significantly associated with their occurrence: type 1 diabetes (odds ratio [OR] = 3.19; 95% confidence interval [CI] = 1.55-6.57) and experiences of asymptomatic hypoglycemia (OR = 2.20; 95% CI = 1.05-4.63). Awareness of the treatment hypoglycemia risk because of information provided by a medical specialist was also but nonsignificantly associated with hypoglycemia while driving (OR = 2.61; 95% CI = 0.86-7.92). Forty-one patients (18%) combined those 3 variables, 20 (49%) of them self-reported hypoglycemia while driving. Thirty-four percent of the patients never carried carbohydrates for hypoglycemia correction. Seventy-six percent do not monitor blood glucose level before driving. CONCLUSIONS: Our questionnaire allowed us to highlight that 19% our cohort of insulin-treated drivers declared experiencing hypoglycemia while driving. Risk factors identified and prevention data collected should help us better target patient education.

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

Conductive Highly Filled Suspensions for an Electrochemical Dispensing Approach to Pattern Full-Area Thin Metal Layers by Physical Vapour Deposition.

This paper presents a systematic approach for the development of highly filled suspensions used for an electrochemical dispensing approach. Electrochemical dispensing is an alternative structuring process to locally pattern PVD full-area thin metal layers with the goal to create contacts on solar cells or circuit boards by anodic metal dissolution. Achieving a narrow patterned line width requires a dispensing paste with a high yield stress, a small particle size distribution and a good electrical conductivity. Therefore this work focuses on the formulation and characterization of dispensing pastes in terms of their rheological and electrical properties and their particle size distribution. Furthermore, the printing performance is evaluated in dispensing experiments. In this study, samples with a yield stress above 5000 Pa and an average particle size below 0.4 µm were produced, resulting in dispensed line widths below 100 µm with a high aspect ratio above 0.6. The lack of electrical conductivity was solved by adding KCl solution to the paste, which will add to the ionic conductivity of the NaNO3 basis paste formulation. With this approach, printed line widths down to 115 µm and etched line widths below 90 µm at high aspect ratio were achieved on 50 nm aluminum layers.

Non-achievement of LDL-cholesterol targets in patients with diabetes at very-high cardiovascular risk receiving statin treatment: Incidence and risk factors.

BACKGROUND: Cardiovascular diseases are the first cause of mortality in patients with diabetes, and LDL-cholesterol is a well-established cardiovascular risk factor. This study aimed to assess rate of LDL-cholesterol target attainment among patients with diabetes at very-high cardiovascular risk treated with statins, and to identify predictive factors of non-attainment of target in this population. METHODS: Patients were recruited in the Nutrition-Diabetes unit of Montpellier University Hospital, France, from 2014 to 2017. We included all consecutive patients with type 1 or type 2 diabetes receiving statin treatment and at very-high cardiovascular risk according to 2016 ESC guidelines, therefore having a LDL-cholesterol target of <1.8 mmol/L. LDL-cholesterol levels were measured upon admission. Variables independently associated with non-attainment of LDL-Cholesterol target were assessed using multivariable logistic regression. RESULTS: 654 patients were included. Mean age was 63.8 years (SD 11.0), 41.9% were women and 42.3% had a history of cardiovascular disease. 59% of patients did not achieve LDL-cholesterol target, with a median value (interquartile range) of 2.4 mmol/L (2.1-2.9) versus 1.4 mmol/L (1.1-1.6) in patients at target. Risk of non-attainment of LDL-cholesterol target value was increased in women (odds ratio [95% confidence interval]: 2.27 [1.62-3.17]) and decreased in patients with history of coronary artery disease (0.64 [0.45-0.89]) or history of stroke or transient ischemic attack (0.59 [0.33-1.07]). CONCLUSIONS: Management of dyslipidemia is suboptimal, even in very-high risk patients with diabetes under statins. Lipid-lowering treatment should be intensified, in particular in very high risk patients with diabetes who are women or in primary cardiovascular prevention. Clinical Trial number: NCT03449784.