This case study investigates mono-crystalline silicon modules from underperforming portions of a utility-scale photovoltaic power plant. Field-collected I-V curves and electroluminescence imaging suggested that increased series resistance was a primary factor driving module degradation. Selected modules were removed from the field for further analysis, including incremental damp heat accelerated testing, which confirmed a progression in series resistance degradation. Two distinct cell degradation behaviors became apparent during the investigation. Cross-sectional scanning electron microscopy (with elemental analysis) and scanning spreading resistance microscopy identified key differences between the two degradation mechanisms, primarily grid finger width and contact resistance. Additionally, the study highlights the reliability implications of retest requirements in International Electrotechnical Commission 61215 for material changes and how they may have mitigated the degradation observed at this site.

State-of-the-art encapsulation cannot prevent the permeation of oxygen into perovskite solar cells (PSCs). Here, we report the finding that p-i-n structured PSCs degrade quickly under oxygen exposure. Oxidation of C60, rather than perovskites, dominates the degradation. Chemical absorption of oxygen by C60 is identified, which impairs its electron transport property. We modify the electron transport layers to address the instability under oxygen exposure. The elongated fullerene C70 is found to react with oxygen orders of magnitude slower than C60. In combination with a compact SnO2 buffer fabricated by atomic layer deposition, which can slow down the oxygen diffusion, the resulting unencapsulated PSCs with C70 retained 90% of their initial efficiency after 1-sun illumination in pure oxygen for 1,200 h at 70°C, improving stability by hundreds of times. Testing of unencapsulated perovskite minimodules of different perovskite compositions with C70 gives extrapolated lifetimes of 17–41 years at 50°C.

Simultaneous changes in photovoltaic (PV) module architecture-such as increased area, replacing the polymeric backsheet with a glass backsheet, and reducing glass thickness from 3.2 to 2.0 mm-have resulted in a novel failure called spontaneous glass breakage. Spontaneous glass breakage results in front and/or rear glass failure without any obvious cause. The resulting low-energy fracture patterns have raised concerns about the thermal strengthening in 2.0-mm glass. We present validation of a nonde structive method for measuring the glass surface stress in PV modules. We use a scattered light polariscope to examine the glass properties of 11 modules from 6 solar fields, with and without spontaneous glass breakage. Based on a Mann-Whitney test p-value of 1.4 & times; 10(-6), we conclude that there is a correlation between lower surface stress and susceptibility to spontaneous breakage. A Kendall's Tau test p-value of 2.0 & times; 10(-4) indicates a correlation between increased module area and lower surface stress. We find that 2.0-mm glass can be, and often is, fully tempered (surface stress >= 69 MPa), but inspecting the fracture pattern is not a reliable way to assess the amount of thermal strengthening. A combination of factors, not just surface stress, influences glass breakage.

We present a performance modeling and degradation analysis framework for tandem photovoltaic modules, building upon established procedures for crystalline silicon devices and adapting them to account for the spectral sensitivity of multijunction technologies. The methodology employs filter criteria to select outdoor measurements close to standard test conditions (STC) under stable spectral and ambient conditions, followed by normalization of power production data with corrections for temperature, irradiance, and precipitable water vapor. We demonstrate this framework using a mechanically stacked four-terminal gallium arsenide (GaAs) // silicon (Si) tandem solar minimodule deployed outdoors from October 2019 to January 2021 in Golden, Colorado, USA. We determined degradation rates of −4.1±0.2%/year for the GaAs subcell and −2.5±0.9%/year for the Si subcell, with analysis of individual performance metrics indicating that packaging degradation, particularly delamination, was the dominant failure mode. Simulations using PVcircuit, an open-source equivalent-circuit solver, confirmed these findings. The presented methodology provides a reproducible foundation for performance modeling and degradation analysis of emerging tandem technologies.

We present a fast, low-cost ultraviolet (UV) spot test to screen photovoltaic modules for UV-induced degradation (UVID). The measurement is based on a fiber-coupled arc lamp that delivers a highly accelerated local UV dose—approximately five years of equivalent field exposure in less than a day. Spot-exposed areas are evaluated using electroluminescence imaging. We test a “known bad” product, which was observed to experience UVID in the field, and a “known good” product which did not exhibit UVID in the field. Results indicate that the method may be useful as a quick and relatively inexpensive quality control screening tool for customers and manufacturers.

We present outdoor observations of metal-halide perovskite modules deployed in the Photovoltaic Accelerator for Commercializing Technologies center, which houses one of the world's broadest efforts to test metal-halide perovskite photovoltaic modules outdoors. As of January 2025, outdoor testing has encompassed over 150 modules from 14 different partners. Our findings illustrate how daily changes in efficiency, driven by exposure to light, affect field performance in real-world conditions. These effects cannot be explained by existing outdoor performance models and frustrate the notion of a traditional temperature coefficient.

Photovoltaic (PV) modules that have a robust package and that pass a minimum of 100 hours of 1-sun irradiance at 55 °C are more likely to retain 80% of initial efficiency beyond 10 weeks in the field. In this work, we describe our progress towards understanding the relationship between light- and elevated-temperature testing and outdoor degradation of perovskite PV modules. We find that a combination of tests is required to confidently screen for early field failures. Here, we discuss field testing and indoor stress testing results from 8 different module batches representing 4 different module makers and a variety of processing conditions and formulations.

We performed cyclic loading of photovoltaic laminates with precracked silicon cells to explore if and how loading frequency and contact pressure influence the ensuing gridline wear-out process. A measurement of parallel resistance across cracked gridlines on a laminated cell coupon was used as the metric for gridline electrical contact degradation. A statistical analysis of variance (ANOVA) analysis of the experimental results discerned that loading frequency is a more significant factor than contact pressure for gridline degradation.

This case study investigates mono-crystalline silicon modules from a utility site flagged as underperforming. Field characterizations revealed suspected damp heat induced series resistance driving module degradation. Select modules were removed from the field and incremental damp heat accelerated testing was conducted. A bimodal distribution of cell degradation became apparent. Cross-sectional scanning electron microscopy, energy-dispersive X-ray spectroscopy, and scanning spreading resistance microscopy reveal the most significant differences between the two are grid finger width and contact resistance. We discuss the reliability implications of re-test requirements in IEC 61215 for bill-of-material changes and how they may have mitigated degradation at this site.

A recent trend in commercial PV modules is a transition to n-type silicon cells, including passivated emitter rear totally diffused (n-PERT), tunnel oxide passivated contact (TOPCon), and silicon heterojunction (SHJ). There is evidence via lab studies that some of these cells are more susceptible to UV induced degradation (UVID), yet there is a lack of confirmation that such degradation occurs in the field. Current IEC standards designed to screen for early module failures require only minimal UV exposure (15 kWh/m(2) 280-400 nm, similar to 2-3 months equivalent outdoor exposure). Here, we investigate fielded n-PERT silicon (Si) modules from a commercial utility that show power losses of similar to 2%/year. We present a comprehensive picture of the physics and chemistry of degradation supported by both module and cell electronic characterization (EL, PL, IV, EQE, and DLIT) and materials-level morphological and chemical analysis (SEM, EDS, XPS, FTIR, and HPLC). All sampled site modules show short circuit current (I-sc) and open circuit voltage (V-oc) losses when compared to unfielded spares, with the most severely degraded also having losses in fill factor (FF). We identify two different degradation modes contributing to overall power loss: (1) external quantum efficiency (EQE) measurements show losses in the blue range of the spectra, indicative of cell surface recombination losses, and (2) variations in high series resistance (R-s) at the cell level that are correlated with compositional differences in cell metallization. Using unfielded spares, we were able to reproduce V-oc, I-sc, and EQE losses via a minimum UV stress of 67.5 kWh/m(2) (280-400 nm), 4.5x the exposure currently required in IEC 61215-2 (MQT 10). Degradation continued with additional UV dosage equivalent to the fielded modules (405 kWh/m(2) total), with power loss leveling out at an average of 6.1%. Subsequent 1000 h of 85% RH/85 degrees C damp heat testing showed that cells exposed to UV underwent additional severe series resistance degradation, even those without the susceptible paste composition seen in the field, whereas non-UV exposed cells saw little change. We attribute this to higher concentrations of acetic acid generated on the UV exposed area of the module, leading to degradation of the gridline/cell interface and high R-s. This study is unique in that it reproduces field observed utility scale UVID with an accelerated test and supports the need for standards development for longer UV exposure combined with other stress factors to catch materials interplay within a module package.

Field testing, failure analysis, and understanding of degradation mechanisms are essential to advancing metal halide perovskite (MHP) photovoltaic (PV) technology toward commercialization. Here, we present performance data from up to 1 year of outdoor testing of MHP modules in Golden, Colorado. The module encapsulation architecture and encapsulant materials have a significant impact on module reliability, with modules containing a polyolefin elastomer (POE) in addition to a desiccated polyisobutylene (PIB) edge seal outlasting modules with only a PIB edge seal or PIB blanket. Nondestructive and destructive characterization of the field-tested modules points to module scribes and interfaces as areas of potential mechanical weakness and chemical migration, resulting in shunt pathways and increased series resistance. Finally, indoor accelerated stress testing with light and elevated temperatures is performed, demonstrating failure with similar scribe degradation signatures as compared to the field-tested modules. Under both outdoor testing and light and elevated temperature conditions, electrochemical corrosion between the copper electrode and the mobile iodine ions appeared dominant, with a significant progression at the scribes that is speculated to result from an interplay between the initial laser damage and joule heating from enhanced ion diffusion under bias.

Developing metal halide perovskite (MHP) photovoltaic (PV) devices into reliable large-area solar modules could accelerate global solar energy deployment. Many MHP devices are susceptible to degradation under light and elevated temperature (LT). Published research on LT testing is limited at the module level, and LT testing has not yet been developed for qualification testing of commercial PV products. This report assesses whether results of LT testing at moderately elevated temperatures correlate with those of field-tested modules from the same batch. Six batches of samples from four manufacturers are assessed. It is shown that modules with a robust package that can maintain over 80% of their peak efficiency during LT testing at 55 °C for 100 h are more likely to retain over 80% of their peak efficiency during outdoor operation for 10 weeks. This finding is a step towards developing a validated test protocol that could be incorporated into a qualification standard for the commercialization of MHP PV technologies.

Photovoltaic (PV) module materials and technologies continue to evolve as module manufacturers and buyers try to minimize costs, maximize performance, and speed deployment. Both silicon and thin film modules are converging toward similar similar to 3m(2) glass-glass designs with thinner glass sheets to increase power output while reducing module weight, and both types are increasingly mounted on single-axis trackers. At the same time, an increasing number of PV sites have been reporting spontaneous glass breakage in early life systems deployed with these "big, floppy modules." In this article, we identify the concurrent module changes that may be contributing to increased early failure, explain the trends, and discuss their reliability implications. We suggest that larger, thinner glass sheets along with variations in heat treatment and quality may be contributing to glass vulnerability. We note that trends toward weaker or back-mounted frames may also be contributing to module failures, especially for "extra-extra-large" modules mounted on trackers. Combinations of these trends may have pushed modules to a threshold at which increasing early failures are causing the front edge of the "bathtub curve" to re-emerge. Current qualification testing appears to be ineffective for catching these early failures in new module designs, and module buyers do not have enough reliability information-or cannot prioritize such information-during module procurement. Additional research is needed to identify the field conditions leading to glass breakage and if there is one or multiple limiting flaws in new module designs causing glass breakage. Early failures may be mitigated by returning to more robust designs or ensuring better module testing and quality assurance.

Metal halide perovskite solar cells have shown promising power conversion efficiencies, but commercialization requires that decent durability is also demonstrated. Under normal operation, solar cells are subject to a complex combination of stressors, such as visible light, ultraviolet light, heat, humidity, mechanical stress and electric potential, which complicates the understanding of failure mechanisms. Existing stress tests do not act as a time machine. In new materials systems such as perovskite photovoltaics, the tests have no known relationship to field service. In this Perspective we recommend following a durability learning cycle that interleaves photovoltaic module engineering with field testing; accelerated testing; and preconditioning and performance engineering. We advocate for field testing to demonstrate real-world performance and identify field-relevant failure modes, and urge the community to develop accelerated and qualification tests that account for device metastability, variations in material composition and different/various processing methods. These practices are more difficult, but more important, than the simple pursuit of higher initial efficiencies. Perovskite photovoltaics have achieved high power conversion efficiencies, yet their durability remains to be proven. This Perspective presents a number of approaches with a view to addressing durability challenges.

The rise of photovoltaics (PV) as a major contributor to energy generation worldwide has also coincided with major changes in module format. In the last ~5 years, utility scale modules have transitioned to a glass-glass package to take advantage of bifaciality, while at the same time decreasing the glass thickness from 3.2 mm to ~2 mm to save on cost and weight. In parallel, modules have continued their trend of increasing in size, with areas of 2.5 - 3 m2 common today. Despite top tier manufacturers testing to current IEC standards, there has been an uptick of modern glass-glass modules spontaneously breaking in the field, sometimes even before the PV plant is brought online. This is of grave concern as even a small number of cracked modules have been observed to cause ground faults and inverter down time. One of multiple possible contributing factors is a change in glass strength, which is dependent on the thickness, flaws, and stress profile from heat treatments of the glass. Our work examines the variability of glass thickness, surface stress, and compression depth in a variety of PV modules, from older glass-backsheet, to more modern glass-glass modules of various sizes. We discuss a procedure developed to get consistent stress measurements on a fully intact module. We find that while most glass panes measured pass ASTM 1048-18 as fully tempered glass, the surface stress of modules known to break in the field is overall lower compared to glass-backsheet and glass-glass modules not known to spontaneously break. Furthermore, we discuss how compression depth, inherently smaller in thinner glass, could contribute to a narrower tolerance of flaws. We discuss how the decrease of both the surface stress and compression depth in modules known to spontaneously break in the field could be one contributing factor increasing probability of failure.

We present outdoor observations on metal halide perovskite modules deployed in the Perovskite Photovoltaic Accelerator for Commercializing Technologies (PACT) Center which represents the world’ broadest effort to test perovskite photovoltaic modules outdoors. Outdoor testing to date has encompassed over 100 modules from nine different partners. Our findings illustrate how daily changes in efficiency, driven by exposure to light, affect field performance in real-world conditions. These effects cannot be explained by existing outdoor performance models and frustrate the notion of a traditional temperature coefficient. We also present observations about the long-term performance of the modules, including symptoms of degradation as they manifest in the field.

Metal halide perovskite (MHP) solar cells are an emerging thin-film photovoltaic (PV) technology projected to play an important role in the terawatt-level PV deployment. However, the lack of long-term operational stability in outdoor environments is currently a major hurdle and technological barrier to commercialization. Limited studies are available on outdoor testing of MHP cells and modules, and differences in cell/module encapsulation, architectures, chemistry, and fabrication processes further complicate our understanding of MHP outdoor reliability and associated degradation mechanisms. The Perovskite PV Accelerator for Commercializing Technology (PACT) center provides independent testing of mini-modules provided by the perovskite community. To date the PACT center has received and tested over 300 modules from 4 Universities and 5 industry providers. Here we present results of post-mortem analysis of encapsulated perovskite modules that underwent a gradual power loss throughout -200 days of field testing. Fully encapsulated perovskite modules exhibit longer field lifetimes compared to early module designs with an edge seal only, with the current T80 record of -140 days. Module scribe-lines were identified as potential weak spots resulting in resistive losses. We observe perovskite morphology deterioration near the scribes caused by chemical degradation. Accelerated stress-test protocols are being developed to build confidence in this new technology faster than the field alone. Initial results suggest that light and elevated temperature leads to similar degradation mechanisms as seen in the field. The role of the polymeric encapsulant on the degradation kinetics and mechanisms is going to be examined.

Cracks can form in Silicon solar cells in photovoltaic modules due to mechanical stresses arising from various extrinsic factors like handling and weather. While the immediate performance degradation may be minor, continuous loading overtime will degrade module performance. One probable reason is gridline surface wear across the cracked silicon with increased cyclic loading. In this work we propose a method to correlate gridline wear to module electrical degradation. We begin by conducting cyclic four-point bending tests on laminated silicon solar cells with a single crack and 22 intact gridlines for 10,000 cycles. We measure the progressive change in resistance during each loading cycle. We correlate it to a length scale called critical crack opening displacement (CCOD) that signifies failure of individual gridlines. By employing Weibull analysis, we determine the characteristic CCOD for all cycles and fit this data to a modified version of a wear power law. We observe that this fits the data well. We also propose to study the effect of individual parameters in the power law equation and extend the equation to include material properties.

This article explores the use of femtosecond (fs) lasers to form glass-to-glass welds for hermetically sealed, polymer-free solar modules. Low-iron solar glass coupons were welded together without the use of glass filler using a fs laser with dedicated optics to elongate the focal plane parallel to the incident beam. The resulting welds were then stress tested to failure to reveal the critical stress intensity factor, K-Ic. These values were used in a structural mechanics model of a 1 m x 2 m glass/glass module under a simulated static load test. The results show that the fs laser welds are strong enough for a suitably framed module to pass the IEC 61215 static load test with a load of 5400 Pa. Key to this finding is that the module must be framed and braced, and the glass must be ribbed to allow pockets for the cells and welds inside the border of the module. The result is a module design that is completely polymer free, hermetically sealed, has improved thermal properties, and is easily recycled.