Perovskite solar cells (PSCs) are a promising emerging technology on the cusp of commercialisation. With record power conversion efficiencies >26%, they are excellent candidates for low-cost and low-embodied energy photovoltaics. Their emergence as a promising technology is timely as we are on the brink of significant climate change and face the limits of current linear economic models. Transition is necessary to ‘circular economy’ with widespread deployment of sustainable green energy technologies. However, the deployment of green technologies, including PSCs, presents significant sustainability challenges, including availability of critical raw materials, environmental impacts of mining and production and waste generation at end-of-life.[1,2] Achieving widespread deployment necessitates a continuous supply of critical raw materials and lifecycle optimisation early in development to ensure true sustainability. This includes minimising production-related environmental impacts, developing end-of-life strategies, designing for longevity, selecting low-impact materials, and substituting primary and critical resources. Here we will discuss the work of the SPECIFIC Innovation and Knowledge Centre and the UNESCO Chair in Sustainable Energy Technologies at Swansea University, which aims to advance the sustainability, understanding and scaling of perovskite photovoltaics.[1-5] It is our contention that perovskite photovoltaics, as an emerging energy technology, have great potential to be designed for a circular economy and optimised end-of-life processing to deliver significant sustainability benefits. We will discuss opportunities for the for distributed manufacturing of perovskite photovoltaics to help transform energy access as well as assessing resource constraints and implementing circular economy strategies.[1] Early evaluation of future waste streams and materials supply issues are essential to avoid technological lock-in and ensure sustainable pathways forward.

Power conversion efficiencies (PCE) exceeding 26% have been achieved by perovskite photovoltaics (PePVs), which have emerged as a promising alternative energy solution. These efficiencies are comparable to classical silicon solar cells. They are appropriate for both low-power applications and large-scale solar farms due to their adaptability. Nevertheless, the preservation of high efficiency in large-area panels under real-world conditions continues to be a substantial obstacle. The complexities of outdoor exposure are not adequately captured by conventional lab-based testing protocols, as the performance and stability of the system are significantly influenced by fluctuating weather patterns and variable peak sun hours.The long-term performance of perovskite modules and panels in outdoor conditions will be the primary focus of this presentation, with an emphasis on the origins of a variety of degradation factors. Some of these factors are intrinsic to the perovskite active layer, while others are extrinsic, such as lamination failure. The effects of gloomy storage and light soaking on the panels and their partial recovery are investigated using detailed measurement protocols.The sensitivity of perovskite panels to environmental conditions such as humidity, high temperatures, and light exposure, which are significant degradation sources, poses a challenge to their long-term stability. Experimental results suggest that the solar farm experiences a more significant degradation during the summer as a result of protracted exposure to high temperatures and solar irradiance, which significantly impedes lamination stability. However, this degradation was discovered to be partially reversible following a period of dark storage. Changes in the light soaking phenomenon (LSP) were observed, as well as enhancements in the electrical parameters of the solar farm following dark storage. The time required for recuperation was contingent upon the severity of the panel degradation. Recovery occurred within the day-night cycle during the initial phases of operation; however, as degradation progressed, additional time was required. Panels were unable to regain their properties with dark storage alone at extremely low degradation levels, necessitating subsequent light exposure for performance recovery. This suggests a multifaceted interplay of degradation and recovery mechanisms that are contingent upon dark storage and light exposure. The rate of degradation of electrical parameters was also influenced by seasonal and environmental conditions, as evidenced by the seasonal behaviour of degradation. Visual inspections revealed that the panels had developed defects over time, which were linked to lamination failure and the penetration of oxygen and moisture. These defects had a negative impact on the panels' performance. The restoration of electrical parameters was impeded by severe optical degradation, even after dark storage. Studying the voltage mismatch of perovskite photovoltaics is another essential stage in the commercialisation of this photovoltaic technology, as it is essential to comprehend its influence on rate of degradation. This encompasses the identification of the most effective connection configuration (parallel and series) for the efficient long-term operation of a solar farm, as well as for the upscaling and fabrication of panels. In summary, the stability of photovoltaic perovskites is significantly influenced by lamination. This research demonstrates that the electrical properties of the panels can be restored provided that the lamination prevents the penetration of external factors (including moisture and oxygen). Nevertheless, it is imperative to conduct additional research on the ageing process in outdoor environments in order to distinguish between recovery scenarios in terms of the extent of degradation and long-term stability.

Accurate predictive models are required for photovoltaic (PV) performance reliability assessment and failure diagnostics [1]-[3]. Studies have shown that machine learning models can accurately predict the power conversion efficiency of perovskite solar cells (PSCs) based on composition and structural parameters [4]-[5]. Machine learning algorithms have been utilized before [6] using indoor stability data sets to predict the outdoor stability of perovskite-based devices. However, machine learning models using high-throughput outdoor stability data from perovskite-based devices to predict their time-series power output is still limited in the literature [7-8].

This work aims to utilize several data-driven algorithms (based on machine learning principles) to predict the power output of different perovskite devices (both single and tandem configuration). Namely, three gradient boosting models (CatBoost, XGBoost and LightGBM) have been employed for predicting the PV performance and output power from perovskite-based devices based on long-term outdoor data. The prediction performance of the different machine learning models was evaluated using yearly datasets containing instantaneous field measurements obtained from the outdoor test site in Nicosia, Cyprus. In all cases, the PV time series dataset was split into a random 70:30% train and test set approach. More specifically, 70% of the dataset was used for model’s training, while the rest 30% was used for testing the accuracy of the models. Prior to the model development, data quality checks were performed [9] along the most influential input parameters using statistics (Pearson correlation) were identified.

For the evaluation of the predictive accuracy of the constructed models, the normalized root mean square error (nRMSE) metric was used [8]. The obtained results demonstrated that all models provide good predictive quality (nRMSE<7%) using the instantaneous measurements. Better prediction performance was provided by the LightGBM regression model which presented the lowest nRMSE (<4%) across the whole test set. Dependence of the prediction accuracy of the models with output power levels was detected with larger discrepancies between the actual and predicted power to obtained at lower power levels.

Evaluation of the performance of the models at different train set data partition as well as at different filtering conditions is underway. This study will provide evidence regarding the dependence of the predictive accuracy on the train set duration, data filtering conditions and irradiance profile classification.

Perovskite solar technology has rapidly transitioned into a commercially viable solution after just over a decade of intensive global research. Distinguished by its high specific power, cost-effective production, and exceptional performance under low-light conditions, it stands out among photovoltaic technologies for its broad applicability. Hybrid organic-inorganic perovskites uniquely combine the ease of solution processing typical of organic small molecules and polymeric semiconductors with the superior physical properties of high-performance crystalline inorganic semiconductors. This synergy results in a novel material class that harnesses the advantages of both organic and inorganic domains.

To enable the large-scale production of perovskite photovoltaics, the adoption of sustainable, safe, and industry-compatible processing methods is essential. Achieving sustainability begins not only with processing techniques but also at the material level. Solaveni, a Germany-based company, has pioneered the sustainable synthesis of perovskite precursors through innovative green halide chemistry. This presentation highlights the benefits of these novel synthesis routes for organic alkylammonium halides and metal halides, evaluated through life cycle assessment (LCA) and benchmarked against conventional production methods. The LCA examines the environmental impacts of these precursor materials—assessing resource consumption, energy use, and emissions—to provide critical insights into their sustainability profiles and ecological footprints. Furthermore, we introduce novel green recycling approaches for perovskite materials that enable rapid dissolution and recovery, fostering the development of a circular economy.

ORIGIN OF DEGRADATION IN THE LONG-TERM PEROVSKITE MODULE OUTDOOR PERFORMANCE IN DIFFERENT OUTDOOR REGIONS

In the domain of perovskite formulations, module architectures, and layer stacks offering possibilities for processing highly efficient devices, comparing performance stability data across literature presents a considerable challenge. While perovskite outdoor stability data has been investigated by some research groups [1][2] [3] most samples, even for many perovskite compositions and architectures, have been relatively short-lived. Specific investigations include extensive datasets, yet measurements are confined to cells[4],[5],[6]leading to conclusions influenced by the small device areas and lack of interconnections. Despite the presentation of high-performing devices showcasing operational stability, the hurdles in achieving fabrication on a larger scale persist. Various consortia and partnerships, involving universities, companies, research institutes, and national laboratories, have been established to address these issues. One such consortium is US-MAP (Manufacturing of Advanced Perovskites), which collects and uniformly reports outdoor performance data for perovskite modules.

Our methodology comprises a reproducible and scalable process, an operationally stable perovskite formulation, and a photo and thermally stable layer stack (layer stack: ITO/NiOx/ FA_0.80Cs_0.20Pb(I_0.94Br_0.06)₃ /ETL/ITO). The robustness of this process is demonstrated by its run-to-run reproducibility, establishing a foundation for an equitable comparison of outdoor performance among samples. We present the real-time performance of our perovskite modules over 4 years and discuss the strategies employed to achieve more extended stability as we scaled up our modules to 800 cm2 [7].

Our innovative approach integrates a feedback loop based on in-lab characterization, outdoor performance results, and degradation analysis to enhance our understanding and enable adjustments for prolonged lifetimes. In the conference we will elaborate on our approach to the performance tests that have led to process modifications, giving rise to new generations of modules characterized by improved performance, stability, and area coverage.

We investigate the data for the correlation between outdoor performance and irradiance levels, alongside temperature variations. Figure 1 displays the mini-module PCE evolution up to the summer of 2024 alongside the temperature variations of the modules. Preliminary analysis suggests a consistent burn-in period for all samples, within the initial 3 months of outdoor deployment. This results in a performance decline of approximately 30% from the initial levels, followed by a performance stabilization over extended durations. From this dataset extending from 6 months in some locations to +4 years in others, we expect to discern dependences on irradiance levels, seasons, climates, and temperatures. Insights from the outdoor deployment of modules in Cyprus highlighted potential reasons for module failure, such as thermomechanical issues or the formation of ionic barriers. Through further investigation and deeper characterization, we aim to determine whether permanent degradation arises primarily from one of these stressors or a combination of both.

Figure 1: Upper plot: PCE evolution over time for samples considered in the study. Lower plot: Module temperature variations for different locations considered in the study.

Using the insights gathered from outdoor performance data, our objective is to refine our perovskite formulation, layer stack, and module design. Looking ahead to future developments, we are focusing on Gen 3 modules, to enhance the performance of our large-area modules while maintaining their exceptional stability.

Perovskite solar cells have exhibited meteoritic growth in their power conversion efficiency (PCE). However, there is a consensus among researchers in the field that the durability of perovskite photovoltaics under real operational conditions still requires considerable improvement. We should identify the dominant degradation mechanisms under multiple stresses in outdoor operation. It is even more complicated due to the well-known (but not still well-understood) metastable day-night dynamics of the perovskite PV. Another key aspect is that PSC degradation rates can strongly depend on electrical bias. We will demonstrate that even mechanisms of such degradation can be different at short-circuit, open-circuit, or maximum power point, for example. Furthermore, we will also report experimental results on the effect of electrical bias on PSC behavior after stress relief, including promoting the recovery process.

Research strategies towards improvement of PSC operational stability exhibiting (at least partially) reversible degradation may include both (1) mitigation of the degradation mechanisms and (2) promotion of the recovery process. Most of the published studies on perovskite PV were aimed at the former strategies. Knowledge about attempts to promote the recovery of perovskite PV is limited. Electrical “therapy” of degraded perovskite solar cells is possible but still should be developed.

Halide perovskite photovoltaics is surging towards commercialization with the first industrially manufactured panels installed in the PV fields. With this, it is more important than ever for the researchers in the perovskite community to focus on identifying all the degradation and failure modes that could be triggered under real-world conditions to finding ways to overcome them.

In this contribution, we will share insights on the topic accumulated over the last 5 years of outdoor studies with perovskite solar cells exposed in Berlin, Germany. After testing a variety of perovskite absorbers, cell architectures and module encapsulation schemes, it is not surprising that we observed a host of different degradation pathways depending on the device architecture, including both extrinsic and intrinsic instability mechanisms [1]. Despite this, champion devices on our test field are already more than 4 years old providing an optimistic perspective of the possibility of reaching the desired operational lifetimes.

Severe failures occur if water vapour enters the device due to flaws in encapsulation. It results in different patterns of damage spreading depending on whether it originates from a specific weak spot (glass crack, imperfect adhesion of the edge sealant, etc.) or the overall high water vapour transmission rate of the encapsulation materials used. We also observe that encapsulation could be responsible for other degradation effects, such as layer delamination or chemical interaction between perovskite and encapsulation materials [2].

Intrinsic device stability, which is not related to the device encapsulation, is also critical. We confirmed such mechanisms as increased ionic losses under outdoor operation (due to electric field screening) [3], increased bulk defect concentration, localized phase segregation, and the formation of macroscopic defects. We also often see a change with ageing in the cell transient behaviour in the day-night cycle patterns. This constitutes another loss mechanism, often referred to as fatigue. Finally, we observed for a range of samples that the device layout can affect the ageing behaviour through various edge effects.

References

[1] S. Baumann, G. E. Eperon, A. Virtuani, Q. Jeangros, D.B. Kern, D. Barrit, J. Schall, W. Nie, G. Oreski, M. Khenkin, C. Ulbrich, R. Peibst, J. S. Stein, M. Köntges, Stability and reliability of perovskite containing solar cells and modules: degradation mechanisms and mitigation strategies. Energy Environ. Sci., 2024,17, 7566

[2] U. Erdil, M. Khenkin,* W. M. Bernardes de Araujo, Q. Emery, I. Lauermann, V. Paraskeva, M. Norton, S. Vediappan, D. K. Kumar, R. Kant Gupta, I. Visoly-Fisher, M. Hadjipanayi, G. E. Georghiou, R. Schlatmann, A. Abate, E. A. Katz, C. Ulbrich, Delamination of Perovskite Solar Cells in Thermal Cycling and Outdoor Tests. Energy Technol. 2024, 2401280

[3] S. Shah, F. Yang, E. Köhnen, E. Ugur, M. Khenkin, J. Thiesbrummel, B. Li, L. Holte, S. Berwig, F. Scherler, P. Forozi, J. Diekmann, F. Peña-Camargo, M. Remec, N. Kalasariya, E. Aydin, F. Lang, H. Snaith, D. Neher, S. De Wolf, C. Ulbrich, S. Albrecht, M. Stolterfoht, Impact of Ion Migration on the Performance and Stability of Perovskite-Based Tandem Solar Cells, Adv. Energy Mater. 2024, 2400720

The transition to renewable energy is critical for decarbonizing global energy systems. Solar panels, alongside wind turbines, play a pivotal role in achieving this transformation. With projected annual photovoltaic production surpassing 1 terawatt peak (TWP) in 2025, the deployment of tens of billions of solar panels is essential to meet energy goals. However, as these panels reach the end of their lifecycle, the challenge of sustainable disposal or recycling arises. Opting for circular recycling over landfilling offers numerous benefits, including the recovery and reuse of valuable materials, which are vital to maintaining production sustainability. This underscores the urgent need for a circular photovoltaic market where production and recycling capacities are aligned.

Lead perovskite solar cells, a next-generation photovoltaic technology, have entered the field as a promising new technology with their high efficiency, scalability, and unique material properties, such as tunable bandgaps and high absorption coefficients. Perovskite solar cells hold both promises and new challenges with respect to recycling and sustainability of photovoltaic technologies. On the one hand, perovskite solar cells can be deposited from solutions, enabling material recovery with very high selectivity. On the other hand, perovskites pose environmental challenges, particularly regarding the sourcing and recycling of lead halides. Addressing this, our research focuses on i) developing circular recovery and recycling processes for all materials used in a perovskite solar cell and ii) integrating perovskite solar cells into a circular economy by repurposing lead waste into materials for new solar cell fabrication.

With respect to circular recycling of perovskite solar cells, we demonstrated a closed-loop recycling of MAPbI3 perovskite solar cells that achieved a 99.97% mass recovery through a layer-by-layer solvent extraction method. Critical components, including ITO glass, SnO2, MAPbI3, and spiro-OMeTAD, were recovered and purified. Devices fabricated with recycled materials maintained performance on par with those using virgin components, with peak efficiencies reaching 19%. A techno-economic analysis showed that implementing this recycling approach could reduce material costs by 63.7% in lab-scale production. These results underscore the potential of closed-loop recycling to enhance the sustainability and cost-effectiveness of perovskite photovoltaic technology​.

With respect to utilizing lead, we developed a recycling process starts to convert contaminated lead into lead iodide (PbI₂). This method achieves near-complete conversion, with a Faradaic efficiency close to 1. An essential step involves purifying the synthesized PbI₂ through single-crystal growth, yielding, in one example, 35% pure PbI₂, while the remaining material is recycled for subsequent loops. This scalable process produces PbI₂ at approximately 1g per hour, with potential for industrial application by increasing electrode area.The recovered PbI₂ is directly utilized to fabricate new perovskite solar cells, achieving efficiencies exceeding 20%. This result not only demonstrates the viability of recycling perovskite materials but also establishes a sustainable pathway for addressing the environmental concerns of lead waste. By converting contaminated lead from various sources, including legacy lead waste from industries and household applications, our approach eliminates significant ecological hazards and contributes to a circular economy.

Chinese companies like Microquanta, GLC Power and Utmolight are already producing perovskite modules and are planning production lines of 1-2 Gigawatts each in the next years. Also for tandem devices perovskites become more and more import, OxfordPV has the first modules on the market and according to the 15th edition of the International Technology Roadmap for Photovoltaics, 10% global market share of perovskite-silicon tandems are estimated for the year 2034.[1] This sounds not so much but will correspond to > 100GW, as for 2028 the global PV market is estimated to be 876 GW. [2]

These upcoming huge amounts in mind, recycling of perovskites will be an important issue in the future and in contrast to silicon modules, there is no existing industrial recycling concept for perovskite modules or perovskite-silicon-tandem modules.[3] Here we will present first results of the PeroCycle project, funded by the Deutsche Bundesstiftung Umwelt (DBU).  Within the project we investigate a direct recycling approach: Perovskite mini-modules are produced and encapsulated at ZSW, in the second step the modules are sent to Solar Materials where the glasses are separated in one piece from the absorber materials. In the third step, the glasses are cleaned and the absorber material is purified at Solaveni. Finally, with the recycled glasses and perovskite materials new modules will be manufactured at ZSW and analyzed to evaluate the feasibility and quality of the recycling process.

Besides recycling, we focus also on stability issues. An outdoor test of our semitransparent modules is running since 18 months at HZB and we carry out damp heat and constant illumination tests.

The long-term stability of perovskite solar cells (PSCs) depends not only on the inherent stability of their device layers but also on the effectiveness of their encapsulation. In commercial photovoltaic (PV) technologies, thermal lamination with over-device sealants, such as ethylene vinyl acetate (EVA) or similar polymeric films, is commonly employed. However, PSCs require an additional edge-sealing layer to significantly reduce water vapor permeation rates, ensuring enhanced protection for the device[1]. 

Glass frit sealants, known for their superior hermeticity and mechanical durability[2], have emerged as a highly effective encapsulation solution for PSCs. When applied through laser-assisted edge-sealing techniques, these materials have successfully protected PSCs under different standard durability tests as outlined by IEC61646 protocols [3, 4]. 

This discussion focuses on the influence of encapsulation hermeticity on the long-term stability of PSCs. Specifically, we examine the impact of the atmospheric composition within the cavity of glass frit-sealed devices. Our study investigates the light-induced degradation of perovskite films sealed under different atmospheres, including air, nitrogen, argon, and carbon dioxide. Results indicate that encapsulated printable HTM-free PSCs demonstrate significantly improved lifetimes when sealed under nitrogen and carbon dioxide atmospheres compared to air.

These findings highlight the role of controlled internal atmospheres in mitigating degradation and ensuring the durability of PSC devices.

Perovskite solar cells have established themselves as the front runner new technology to enter the PV market. Their fast development is now promising that both single-junction and tandem perovskite modules will soon enter industrial production. First modules have reportedly already been commercially available, nevertheless, there are still things to learn about perovskite field operation, arising questions about their long-term stability. While stability is an important and often researched topic, the large scale stability tests have not been performed often. Instead, typically only the stability of the champion device is shown. Several factors contribute to that, such as complex and expensive equipment as well as availability of a large number of similarly performing perovskite devices.

In the presentation, we will show our recent results obtained with the in-house developed WLED system that is designed for simultaneous long-term MPP tracking of up to 144 perovskite solar cells. Besides discuss reproducibility of our devices, the influence of light intensity on stability of the devices, and compare stability under cyclic and continuous illumination. Special focus will be paid to disentangling humidity and light as main degradation stressors for perovskite devices. For that, capping of devices with Al₂O₃ is implemented, enabling long-term testing without moisture degradation. This makes long-term measurements in air are possible without the need for encapsulation, which should accelerate mass testing of perovskite solar cells. Finally, we will also discuss aspects of perovskite tandem solar cell testing and present a dedicated bichromatic setup for their testing.

Laboratory-scale power conversion efficiencies (PCE) of ABX3 type perovskite solar cells have surpassed 26%. However, the typical solution-processed methods, involving spin-casting, antisolvents, or gas quenching, and using N,N-Dimethylformamide (DMF) and Dimethyl sulfoxide (DMSO) solvent systems, pose scalability and stability challenges. To address this, we optimized a DMF/DMSO and antisolvent-free solvent system for 1.48eV FAPbI3-based p-i-n architecture solar cells using 2-methoxyethanol (2-ME). We incorporated N-Methylpyrrolidone (NMP), a non-volatile and Pb2+ coordinating additive, to inhibit non-perovskite phase formation during room-temperature deposition. Unlike common Pb2+ coordinating agents such as DMSO, DMPU, or DMAc, our method showed no precipitation at any concentration. With high reproducibility, we achieved a stable maximum power point tracking (MPPT) of ~23.00% for a 0.25 cm2 and ~22% on a 1 cm2 aperture area, attributed to enhanced photoluminescence quantum efficiencies (~8%), compact and pinhole-free morphology, and a highly oriented crystal structure. This technique is easily scalable for larger areas. Despite these efficiency gains, stability remains crucial for commercial viability. Our study investigates the high stability of optimal bandgap FAPbI3 perovskite using in-situ 2D XRD. For examples: we stressed thin films at 130°C and 50% RH, noting that DMF films turned yellow, while 2-ME films retained their black phase. Optoelectronic and Photovoltaics Devices response tests revealed ~no degradation in 2-ME films and devices, following Damp Heat, ISOS-D2 and ISOS-L3 protocols. Loss quantification using half-stack PLQE measurements identified the perovskite/C60 interface as the performance limiter.

Besides demonstration of scalable processes for realization of perovskite based photovoltaics, stability of corresponding devices under operating conditions needs to be demonstrated to rationalize their industrial fabrication and marketability. To this end, we investigated outdoor stability of encapsulated 4-terminal perovskite-silicon tandem modules. In parallel, the stability of the individual devices in a single junction architecture was tested, i.e. of silicon solar cells illuminated with a spectrum not filtered by the wide band gap perovskite top cells and of semitransparent perovskite single junction modules without silicon solar cells at their back.

It is quite frequently discussed that applied load, e.g. by tracking the maximum power point (MPP) of the device under test, can positively affect stability, possibly due to a higher concentration of free charge carriers under open circuit conditions [1]. We performed comparative stability tests with devices in single or tandem configuration and held at open circuit or maximum power point and could not find significant changes with regards to device stabilty, which confirms one of our earlier studies on single junction perovskite modules [2]. Periodic scans of the full IV curves of all devices allowed tracking of individual solar cell figures of merit and their analyses in dependence of e.g. illumination conditions or temperature.