Identifying suitable locations for solar photovoltaic (PV) systems is key to a successful global energy transition. However, PV assessments vary widely in terms of input data used, methodological approaches applied, and therefore ultimately in the resulting total potentials, making their comparison and interpretation challenging. Here, we review the current literature with respect to existing definitions of potentials, associated criteria as well as methodologies to identify current trends in this field and potential future research directions with a focus on large-scale assessments covering at least an entire country or a large region within a very large country. We observed a wide range of assumptions and methodologies used in such studies, sometimes combined with lack of transparency in documentation. Furthermore, the literature lacks consideration of system integration costs to account for the variable PV generation profile. The inclusion of non-technical factors is challenged by the lack of consistent theoretical and methodological approaches and interdisciplinary collaborations, as well as limited availability of data. Combined with a frequent lack of validation attempts, these aspects ultimately limit the comparability and reliability of results. The comprehensive overview in this review assists modelers and decision makers in utilizing best-practice methods for PV potential assessments to improve traceability and comparability of future assessments.

Identifying real-world degradation modes in perovskite solar cells (PSCs) and reproducing them through accelerated aging tests are accomplishments that remain elusive, and this limits progress toward commercialization. Here, we identify three coexisting, spatially non-uniform degradation modes in PSCs following 20 months of outdoor operation: copper corrosion, edge patterns, and phase segregation. By varying light intensity (1 and 2.3 suns) and electrical bias (at the maximum power point [MPP] or open-circuit [OC] conditions) as key stressors, we reproduce and accelerate all three mechanisms. Furthermore, we demonstrate how the interplay of stressors can alter the manifestation of each degradation mode. Among them, phase segregation is the most spatially dominant mode outdoors, and it results in irreversible, micrometer-scale domains. Nevertheless, external stimuli induce optoelectronic changes in these domains that we associate with the metastability observed outdoors. This work links real-world degradation modes to accelerated aging tests, reveals their spatial signatures, and points toward mechanism-targeted acceleration.

Building-integrated photovoltaic (BIPV) systems present a promising avenue for integrating renewable energy generation into urban environments. However, they pose unique challenges, including higher planning efforts and reduced yield generation compared to conventional rooftop systems. Despite these challenges, the double use of area and the high potential in urban landscapes offer compelling advantages. Modules have become highly customizable to fit architect’s requirements in sustainable yet also aesthetic building material. This paper discusses the results of a “living laboratory” in Berlin, which is both a typical building with a ventilated curtain wall and a unique showcase for BIPV technology. Through careful analysis of various factors, including module positioning, ventilation, and shading, this study demonstrates the feasibility and practicality of BIPV integration. The “living lab” not only highlights the technical viability of BIPV systems but also underscores their potential to enhance architectural aesthetics and promote sustainability and carbon-neutrality in urban landscapes.

The commercial viability of promising perovskite photovoltaic technologies hinges on their ability to achieve multidecade operational lifetimes, driving a global effort to design accelerated aging tests that can reliably predict real‐world stability. However, establishing a link between indoor and outdoor degradation remains challenging, as it typically requires sophisticated characterization techniques that are difficult to implement and interpret. In this work, we demonstrate how coupling physics‐based modeling with a probabilistic Bayesian framework allows us to validate the relationship between indoor and outdoor degradation pathways of perovskite solar cells (PSCs) using readily available current–voltage curve data. Our findings reveal that bulk trap density is a dominant degradation mechanism common to p‐i‐n PSCs tested under various indoor and outdoor conditions, while new degradation modes not yet observed during outdoor exposure emerge under elevated stress levels. Furthermore, they emphasize the need to move beyond efficiency‐based lifetime metrics toward a mechanistic framework that can uncover potential failure points. This flexible approach can guide the design of predictive accelerated testing protocols while offering broad applications for optimizing fabrication processes and assessing performance across the solar industry and beyond.

Perovskite solar cells (PSCs) are expected to transform the photovoltaic market; however, their unproven operational stability requires urgent attention, particularly accelerated aging tests. Currently, illumination is the primary stressor in such tests. In this work, we present an accelerated aging procedure consisting of prolonged forward biasing followed by a dark storage (postbias rest) phase, conducted entirely in the dark. During aging under forward bias, ion migration led to impeded charge transport, macroscopic defect growth, and an adverse response of the cells to short light soaking, all of which recovered in the postbias rest phase, yet resulted in increased recombination due to redistribution of ions. We found that outdoor operation of PSCs in Berlin, Germany, over a 20-month period exhibited similar dynamics, with periods of higher temperature and irradiance (spring-summer) aligning with the forward bias phase and cooler, dimmer periods (fall-winter) aligning with the postbias rest phase. This paves the way for accelerated aging tests that can mimic ion migration-induced degradation outdoors without requiring an illumination source.

Encapsulation is a critical topic to ensure the successful implementation of perovskite photovoltaics. Recently, vacuum lamination has been shown as a promising approach that combines compatibility with current industrial processes in conventional photovoltaic (PV) manufacturing and suitability to achieve good results with perovskites. Here, we explore some of the attractive encapsulation materials in terms of their ability to prevent moisture ingress, withstand elevated temperatures, and have suitable mechanical properties to avoid thermomechanical issues. We utilized the previously suggested concept of the "perovskite test," an optical test with simple sample fabrication, for evaluating encapsulation quality and validated the findings with the full solar cell stack. Unsurprisingly, encapsulants without an edge sealant showed insufficient protection from moisture. Ionomer in combination with butyl edge seal showed the best barrier properties; however, this stack led to rapid delamination of the cell layers in thermal cycling tests. Configuration with only edge sealant does not have such an issue in principle (no mechanical stress applied), but an absence of the polymer in the stack is unfavorable in terms of optical design and sometimes showed perovskite degradation that we assign to trapped moisture in the butyl itself. Polyolefin with butyl edge sealant is not free of degradation but showed the most promising compromise by passing the damp heat test and showing fewer issues in the thermal cycling experiments. In general, our material study and optimization presented in this manuscript show that a holistic approach is needed when choosing an optimal encapsulation scheme for perovskite devices.

Tandem solar cells can surpass the limitations of single-junction devices, promising increased performance due to lower thermalization losses. Even though many research and industrial upscaling efforts are based on perovskite-Si tandems, all-thin-film photovoltaic (PV) devices, for instance with chalcopyrite (CIGSe) and perovskite, can offer many advantages such as significant cost and material savings and access to niche markets like building integrated- and flexible PV. However, long-term stability and outdoor performance of perovskite-based tandem devices is to this day challenging. This work presents the first data analysis of year-round outdoor measurements (mpp-tracked) of a perovskite-chalcopyrite tandem device with a starting efficiency of about 23.14% before encapsulation. The maximum outdoor performance of the tandem device changed during the period of observation, reaching the peak performance in April and then decreased due to the device degradation. At its maximum outdoor performance, the tandem could reach up to 68% higher instantaneous power output, relative to its single-junction reference (CIGSe-SJ). In addition, a quantitative time series performance analysis, exemplary qualitative imaging characterization of the tandem before and after outdoor exposure, is shown. Finally, the possibility of predicting the immediate performance of an all-thin-film tandem is verified by using a multiple linear regression model with accuracies generally exceeding 90%.

Insights are reported from a 4-year outdoor study in Berlin using encapsulated p-i-n perovskite solar cells with the structure ITO | 2PACz | Cs0.15FA0.85PbI2.55Br0.45 (bandgap of 1.65 eV) | C60 | SnO2 | Cu. Peak summer performance showed little to no degradation during the first two summers and only approximate to 2% absolute drop in outdoor power conversion efficiency from the first to fourth summer. Despite good stability, the devices exhibit significant seasonality, with winter performance up to 30% lower than in summer during the first year, increasing with aging. The factors contributing to this seasonality are separated into four categories: I) solar spectrum, II) device temperature, III) maximum power point tracking losses, and IV) metastability effects. Among these, metastability - particularly light-soaking behavior - is the largest contributing factor that sets perovskite technology apart from conventional photovoltaics. It was found that in cold, low-light winter conditions, voltage gains from light-soaking remain unsaturated, leading to reduced performance. Full saturation requires more than 24 h of continuous illumination, indicating that device performance depends on more than a single diurnal cycle. This comprehensive analysis highlights the complexity of seasonal behavior and the importance of long-term, real-world testing for accurate forecasting of perovskite photovoltaic energy yield.

Photoluminescence (PL) spectroscopy is a valuable tool fordegradation studies of perovskite‐based photovoltaic materials. The wavelength‐sensitive nature of the photo‐induced processes implies a preference for sunlight as the photo‐excitation source for such PL studies. This study reports on the design and experimental validation of a new setup for the in situ study of PL degradation in metal halide perovskites using concentrated natural sunlight in a wide range of solar concentrations and sample temperatures. The system allows the sample to be excited with the entire solar spectrum while successfully filtering undesired reflected sunlight using two orthogonal polarization filters. Depending on temperature and solar concentration, we observed three types of perovskite PL behavior: stable PL response, without degradation; reversible PL degradation with stable ultraviolet–visible light absorption; and nonreversible PL degradation accompanied with the variation of light absorption.

Halide perovskite is a material that shows great promise in producing renewable energy. It offers one of the most efficient forms of photovoltaics for large-scale production. However, while perovskite solar cell devices are more efficient than many established technologies, their long-term stability outdoors is still being determined. Most studies have tested the stability of perovskite solar cells by keeping them under continuous illumination at maximum power point tracking for hundreds to a few thousand hours. Increasing the temperature has been proposed to accelerate degradation and project data collected relatively quickly to years of outdoor operations. However, PSCs undergo extensive degradation recovery during the resting time in dark and transient dynamics during the illumination they experience in day-night cycling. Therefore, an ageing protocol based on maximum power point tracking under continuous illumination cannot enable quantitative prediction of outdoor performances. To address the challenge of predicting the outdoor stability of perovskite solar cells, we have demonstrated how ageing perovskite solar cells under light/dark cycling that reproduces outdoor functioning with controlled temperature and illumination conditions allows a predictive analysis. Our ageing protocol can accelerate the degradation of perovskite solar cells up to 46 times, i.e. 6 months of indoor testing can reproduce the standard 25 years of outdoor functioning. This result will speed up the studies of perovskite solar cells' stability and their commercialisation.

Perovskite-based solar cells exhibit peculiar outdoor performance which is not yet fully understood. The results of outdoor tests may contain hidden, but valuable information that cannot be fully extracted from measurements alone. One such phenomenon is the effect of nighttime degradation and the subsequent light-soaking recovery, which can take from a few hours in the morning up to the entire day. In this work, long-term outdoor monitoring is combined with energy yield modeling to qualitatively and quantitatively investigate the effect of light-soaking recovery in both single junction and tandem perovskite-based devices. Following the novel methodology presented in this study, it is observed that the light-soaking effect depends not only on the daily irradiation but also on the device temperature, and it can be described using a simple empirical formalism. Incorporating this dependency into the energy yield model results in an excellent agreement between the simulated and the measured outdoor data, which allows to perform long-term prediction studies. The model estimates that the light-soaking metastability effect decreases the attainable annual energy yield by up to approximate to 5% for the studied single junction devices, and for tandems by up to approximate to 3%, depending on the geographical location, and even more for non-optimal device orientation. Long-term outdoor monitoring data are combined with energy yield modeling to quantitatively and qualitatively investigate the effect of light-soaking metastability in both single-junction and tandem perovskite-based PV devices. Using a novel empirical formalism, the energy harvesting losses associated with the light-soaking effect are analyzed for different types of devices operating in different geographical locations. image

This work summarizes various degradation mechanisms relevant for perovskite photovoltaics on different levels from the single layers over (tandem) solar cells to solar modules hereof and their mitigation strategies to enable reliable solar modules.

The stability of perovskite-based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and all-perovskite TSCs using scan-rate-dependent current-voltage (J-V) measurements with drift-diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion-freeze power conversion efficiency from >31% for Si/perovskite and >30% for all-perovskite tandems to approximate to 28% in steady-state. Moreover, the ions cause a substantial hysteresis in Si/perovskite TSCs at high scan speeds (400 s(-1)), and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all-perovskite tandems, subcell-dominated J-V characterization reveals more pronounced ionic losses in the wide-bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite-based TSCs which helps to separate ion migration-related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stability.

The long-term outdoor performance and stability of Perovskite Solar Cells showed several features that stem from the device's meta-stability. To rationalize this behavior we need indoor ageing experiments with cycled light.

For the commercialization of perovskite solar cells (PSCs), detection of associated degradation mechanisms and mitigation of their effect is of paramount importance. The former requires outdoor and indoor stability tests to detect these mechanisms under real operation conditions and to accelerate them under controlled environments. Herein, the thermomechanical stability of encapsulated PSCs in outdoor tests at three locations coupled with indoor thermal cycling tests is investigated. Results show that encapsulant-induced partial delamination can occur in outdoor and indoor tests, leading to disruption in device integrity and substantial loss in the cell active area and short-circuit current. The findings suggest that delamination involves C60 and SnO2 layers as the mechanically weakest point in the device stack. To the best of our knowledge, this work is the first demonstration of delamination in encapsulated PSCs under real operation conditions. While partial delamination emerged on some of the cells exposed in Israel and Cyprus in just a few weeks, it did not occur in Germany over 2.5 years of outdoor exposure. This highlights the importance of multiclimate outdoor testing to validate the significance of failure modes observed through accelerated indoor testing. Investigation of encapsulated perovskite solar cells (PSCs) in indoor and outdoor tests reveals thermomechanical stability concerns. Partial delamination particularly affects C60 and SnO2 layers and disrupts device integrity, leading to losses in cell active area and current. Variability in delamination occurrence across outdoor testing locations highlights the necessity of multiclimate outdoor testing.image (c) 2024 WILEY-VCH GmbH

One major factor affecting the energy yield of photovoltaic modules is the spectral distribution of incident solar radiation. As spectral irradiance data is scarce, this study provides further documentation of recorded spectra at tilt angle 30°– 45°over a period from one to several years, with the resulting distributions of average photon energy (APE) in the 350–1050 nm wavelength range, from five locations in northern Europe. The results show a general trend of higher monthly APE values in summer and lower values in winter, with more pronounced APE variation at increasing latitude. Compared to the reference APE value of 1.88 eV, the largest variation in monthly APE is seen for the northernmost location of Grimstad, Norway, ranging from 1.82 eV to 1.93 eV between January and July with an annual average APE of 1.90 eV. The smallest variation is found for Merklingen, Germany, ranging from 1.86 eV to 1.88 eV between March and July, with an annual average APE of 1.86 eV. Comparing the annual average APE values of the various locations, the study shows a slightly blue-shifted spectrum for Berlin, Enschede and Grimstad, whereas Merklingen experiences a slightly red-shifted spectrum and the APE at Utrecht is similar to the standard reference spectrum. The simulations through SMARTS show air mass, water vapor and aerosols as the major parameters affecting the spectrum. During the winter months, distinct contributions from both clear and cloudy sky conditions result in a bi-modal APE distribution for all locations, which is not observed during the summer months. Analysis of APE demonstrates different site-specific behaviors, even though all sites are categorized in the same Köppen–Geiger (KG) climate class. These differences arise mainly due to atmospheric factors, whereas dissimilarity in albedo conditions, plane of tilt and instrumentation also have some contributions.

Faults in photovoltaic arrays are known to cause severe energy losses. Data-driven models based on machine learning have been developed to automatically detect and diagnose such faults. A majority of the models proposed in the literature are based on artificial neural networks, which unfortunately represent black-boxes, hindering user interpretation of the models’ results. Since the energy sector is a critical infrastructure, the security of energy supply could be threatened by the deployment of such models. This study implements explainable artificial intelligence (XAI) techniques to extract explanations from a multi-layer perceptron (MLP) model for photovoltaic fault detection, with the aim of shedding some light on the behavior of XAI techniques in this context. Three techniques were implemented: Shapley Additive Explanations (SHAP), Anchors and Diverse Counterfactual Explanations (DiCE), each representing a distinct class of local explainability techniques used to explain predictions. For a model with 99.11% accuracy, results show that SHAP explanations are largely in line with domain knowledge, demonstrating their usefulness to generate valuable insights on model behavior which could potentially increase user trust in the model. Compared to Anchors and DiCE, SHAP demonstrated a higher degree of stability and consistency.

Real world solar spectra are rarely equal to those under standard test conditions, which points to the importance of measuring, analyzing and understanding the implications of solar spectra variations in photovoltaic performance. This work presents and analyzes one year of solar spectra measured with installed spectrometers at optimum and vertical (building-integrated-photovoltaics relevant) angles in central Europe, reporting for the first time experimental datasets measured simultaneously over such timespan. In addition, we quantify the differences between these datasets with known key performance indicators and discuss the implications of spectral changes on the maximum current density of ideal single-junction and tandem devices for both installation angles.

The next technological step in the exploration of metal-halide perovskite solar cells is the demonstration of larger-area device prototypes under outdoor operating conditions. The authors here demonstrate that when slot-die coating the halide perovskite layers on large areas, ribbing effects may occur but can be prevented by adjusting the precursor ink's rheological properties. For formamidinium lead triiodide (FAPbI(3)) precursor inks based on 2-methoxyethanol, the ink viscosity is adjusted by adding acetonitrile (ACN) as a co-solvent leading to smooth FAPbI(3) thin-films with high quality and layer homogeneity. For an optimized content of 46 vol% of the ACN co-solvent, a certified steady-state performance of 22.3% is achieved in p-i-n FAPbI(3)-perovskite solar cells. Scaling devices to larger areas by making laser series-interconnected mini-modules of 12.7 cm(2), a power conversion efficiency of 17.1% is demonstrated. A full year of outdoor stability testing with continuous maximum power point tracking on encapsulated devices is performed and it is demonstrated that these devices maintain close to 100% of their initial performance during winter and spring followed by a significant performance decline during warmer summer months. This work highlights the importance of the real-condition evaluation of larger area device prototypes to validate the technological potential of halide perovskite photovoltaics.

While perovskite solar cells have reached competitive efficiency values during the last decade, stability issues remain a critical challenge to be addressed for pushing this technology towards commercialisation. In this study, we analyse a large homogeneous dataset of Maximum Power Point Tracking (MPPT) operational ageing data that we collected with a custom-built High-throughput Ageing System in the past 3 years. In total, 2,245 MPPT ageing curves are analysed which were obtained under controlled conditions (continuous illumination, controlled temperature and atmosphere) from devices comprising various lead-halide perovskite absorbers, charge selective layers, contact layers, and architectures. In a high-level statistical analysis, we find a correlation between the maximum reached power conversion efficiency (PCE) and the relative PCE loss observed after 150-hours of ageing, with more efficient cells statistically also showing higher stability. Additionally, using the unsupervised machine learning method self-organising map, we cluster this dataset based on the degradation curve shapes. We find a correlation between the frequency of particular shapes of degradation curves and the maximum reached PCE.