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In this study, we highlight some important factors in the specimen preparation methods for evaluating photovoltaic backsheet properties after accelerated aging. Two different sequences are considered: Method (I) cut‐then‐age: cut into 1‐cm wide strips and then expose to stress, and Method (II) age‐then‐cut: expose a larger sheet to stress and then cut into 1‐cm widths for mechanical property measurements. We also compare the effect of three cutting methods, (a) tensile specimen punch, (b) paper cutter, and (c) fresh razor blade. Several commercial backsheets were evaluated, with stress exposures including (a) pressure cooker test (PCT), (b) dry ultraviolet (UV) radiation exposure, and (c) UV combined damp heat tests. Fourier transform infrared spectrometer (FTIR) and intrinsic viscosity (IV) were used to analyze the materials on unstressed materials and samples exposed to PCT. The results show that both the cutting method and the time of cutting have an impact on the backsheet mechanical properties. Under UV exposure, Method II, age‐then‐cut, generally resulted in a higher average value, with more variation than Method I; however, if the side strips from Method II were excluded, the variation dropped to the same level. This is because the specimens at the sides of the sheet get additional damage from UV light from the exposed sides of the sample. In contrast to UV exposure, PCT specimens prepared by Method II result in lower average values and higher variability. This is attributed to embrittlement through the bulk of the sample where the cutting of embrittled specimens appears to result in more edge defects which can then initiate a break at smaller strains. The data suggest that for UV exposures, the specimens should be cut after aging and the exposed side specimens discarded, and that for PCT exposures, the specimens should be cut before the exposure. [ABSTRACT FROM AUTHOR]

Abstract This paper analyzes the mechanisms for corrosion and delamination observed in Si photovoltaic modules subjected to high temperature and humidity with a negative-ground bias testing. Based on the thermodynamic data, the ionic component of the leakage current causes reduction reactions of water on the cathodic metallization, producing hydrogen gas and hydroxide ions. Ag fingers are strong catalysts for this reduction reaction compared to other materials used in solar cells and can be the initiation sites of corrosion and delamination caused by the electrochemical reactions. The produced hydrogen gas accumulates inside the module potentially producing a high gas pressure that can promote delamination, which is often preferentially initiated on metallization where the adhesion strength is lower [1–3]. The local basicity near the metal surface increases due to the hydroxide ion generation. Thus, the environment inside the encapsulant can be alkaline despite the presence of acetic acid decomposition products from the encapsulant. Corrosion of materials such as Si used in solar cells occurs and the extent depends on their corrosion resistance to the alkaline solution. This suggests that corrosion and delamination are interactive and promote the formation and propagation of one another. Highlights • The ionic component of leakage current causes water reduction under negative bias. • Produced hydrogen gas potentially produces a high pressure and promotes delamination. • Local alkalinity increase due to hydroxide ion generation can cause corrosion. • EVA can has an alkaline environment under negative bias conditions. [ABSTRACT FROM AUTHOR]

There are relatively few field studies on the degradation of non-fluoropolymer-based backsheets, and understanding their in-field behavior is critical for further development of such products. In this study, backsheet degradation of modules with one of these new types of backsheets (polyethylene naphthalate (PEN)-based) was documented at a four-year old utility-scale array located in Maryland (USA). Visual inspection, colorimetry, glossimetry, and Fourier-transform infrared spectroscopy (FTIR) revealed highly varied properties depending on module position within the array. Specifically, modules near the edge of the array and with higher mounting elevations underwent greater amounts of backsheet degradation, as indicated by yellowing and gloss-loss. The reason for these unique degradation patterns were differential backside exposure conditions, especially of ultraviolet light. This was strongly influenced by the array design, including array structural and environmental factors, such as module spacing and ground cover, respectively. Within the array, no clear link between backsheet degradation and module output or safety has been identified. However, such a relationship may be expected to become more pronounced with time, affecting system lifetime and ultimately the levelized cost of electricity (LCOE). The observed phenomena have implications for both backsheet product development and array design, especially for modules that utilize newer classes of non-fluoropolymer-based backsheets which are typically more susceptible to environmental degradation. [ABSTRACT FROM AUTHOR]

Recycling is an important circular economy strategy, and for photovoltaics (PV), the one that has received the greatest research attention. Recycling of PV modules is required in Europe; everywhere else it competes in the market of end-of-life options, where cost is a primary decision factor. The vast majority of PV modules sold globally are crystalline-silicon (c-Si); most of the rest of the market are cadmium telluride thin film modules whose primary manufacturer runs its own commercial-scale recycling program. While many different c-Si recycling approaches and technologies have been proposed, they generally lack accompanying cost estimates or enough process information to model costs. Herein we develop detailed estimates of seven categories of capital and operating costs along with estimates of revenue from recovered materials for each step in two proposed recycling processes for c-Si PV modules. Using these results, we develop a hypothetical third recycling process merging process steps from the original two, estimate surcharges required to achieve minimum sustainable prices for each recycling process, as well as consider how economies of scale could reduce costs. Increasing the purity of and identifying higher-value markets for recovered materials are approaches to reducing costs and increasing recycling rates in voluntary markets. [ABSTRACT FROM AUTHOR]

Photovoltaic module degradation from a high system voltage is a prevalent degradation mode in the field, where the enabling degradation mechanisms are inherently dependent on the voltage bias polarity of the installed system. Here, the effects of positive bias on module performance are confirmed and the underlying chemical degradation processes are more thoroughly investigated to reveal different degradation pathways from those previously reported in negative bias studies. When cells are under +1000 V stress, crystalline silicon mini-modules with poly(ethylene-co-vinyl acetate) (EVA) encapsulant demonstrated a significant photocurrent loss due to EVA discoloration and delamination from increased chemical reactivity at the front-side EVA/cell metallization interface. Brown discoloration of the EVA encapsulant near the cell gridlines is linked to an electrochemical reaction at the Ag gridlines under hot and humid conditions (85 °C, 85% relative humidity). Chemical compositional analysis using X-ray photoelectron spectroscopy (XPS) confirmed that the discoloration is attributed to the formation of silver sulfide (Ag 2 S) and/or silver oxide (Ag 2 O) species at the EVA/Ag gridline interface. The subsequent migration of Ag ions from the cell gridlines into the bulk of the EVA was evident from XPS depth profiling and optical microscopy. However, the Ag signal was not detected at the EVA/glass interface, inferring limited ionic transport through the nominally 0.45 mm thick encapsulant. For the samples studied herein, the sulfur is believed by the process of elimination to come from the ambient air, diffusing into the module through the permeable polymer backsheet. • High system voltage degradation of PV modules is dependent on the voltage bias polarity. • Positive bias voltage stressed modules demonstrated higher photocurrent loss. • Brown discoloration and delamination observed at EVA/cell gridline interface. • XPS determined oxidation and sulfurization of silver gridlines along with Ag migration into the bulk of EVA. • No evidence of silver at EVA/glass interface. [ABSTRACT FROM AUTHOR]

Controlled delamination of thin-film photovoltaics (PV) post-growth can reveal interfaces that are critical to device performance yet are poorly understood because of their inaccessibility within the device stack. In this work, we demonstrate a technique to lift off thin-film solar cells from their glass substrates in a clean, reproducible manner by first laminating a polymeric backsheet to the device and then thermally shocking the system at low temperatures ( T ≤ -30 °C). To enable clean delamination of diverse thin-film architectures, a theoretical framework is developed and key process control parameters are identified. Focusing on cadmium telluride (CdTe) devices, we show that the lamination temperature and device architecture control the quality of lift-off, while the rate at which the film stack is removed is controlled by the delamination temperature. Crack-free CdTe devices are removed and successfully recontacted, recovering up to 80% of the original device efficiency. The areal density of these devices is ∼0.4 kg m -2 , a reduction of over an order of magnitude relative to their initial weight on glass. The framework developed here provides a pathway toward both the development of inexpensive, flexible PV with high specific power and the study of previously buried interfaces in thin-film architectures.

This article examines different aspects of the history of medicine in the correspondence of the Swiss physician and scientist Johann Jakob Scheuchzer (1672--1733) from Zurich. The focus is on three different levels: persons, contents and functions. On all three levels we can observe that "medicine" takes in some way part of the res publica litteraria. The international correspondence network of Scheuchzer can be seen as a crucial "multiplicator" of communication within the scientific community.