This talk will consider practical approaches for fabricating perovskite solar modules that use commonly available machinery rather than relying on novel or highly industrialized equipment. For example, the use of screen printing methods significantly reduces financial barriers, making advanced solar technology more accessible, especially in under-resourced areas. By focusing on machinery and tools that are widespread and easily obtainable globally, this approach democratizes the production of perovskite modules, ensuring that even communities in less affluent economies can participate in renewable energy advancements. The strategy intentionally avoids the use of overly expensive materials such as Spiro OMeTAD or gold, further contributing to the cost-effectiveness of the production process. If the factory cost entry-point can be driven down without overly compromising on performance then the manufacturing of perovskite solar modules can represent a key advancement in distributing solar energy solutions more equitably across different economic landscapes. The overall aim is to foster a more inclusive approach to renewable energy technology, making it a feasible option for a broader range of global communities.

Despite its current predominance in the photovoltaics (PV) energy market, silicon is being gradually complemented with other photovoltaic materials, able to simplify the production processes, lower the costs, as well as improve the overall efficiency performance. Among these new materials, perovskites can lead to solar cells with a very high efficiency (33.7% ESTI certified efficiency in May 2023[1]), These results have attracted major interest and significant investments toward their industrial scale-up.

Nevertheless, as perovskite solar cells (PSC) electrical properties vary over time due to various meta-stability related factors (material diffusion, chemical imbalance as well as temperature, measurement set-up, light and/or voltage bias triggers..), repeatability of the I-V curve is not always granted, and many uncertainties related to the PSC characterization process are still under scrutiny. In fact, for PSC at present there is not one recognized evaluation technique grounded on international standards yet.

Additionally, PSC contain compounds that require very accurate handling ways, either due to their tangible health-hazard nature or because they can still be considered valuable for the new production chain. These observations raise the need to develop an effective material recovery/recycle strategy to reduce the life cycle impact of this technology before it hits industrial scale production.

The Joint Research Center (JRC) of the European Commission is currently carrying on the “Recycle-PSC” project (Evaluation, assessment and improvement of Process for Recycling and Reusing Innovative). Recycle PV focuses on both aspects of the measurement and characterization of PSC, as well as on the assessment and improvement of certain recycling processes to recover and reuse the materials comprising a PSC, with the aim of developing a safe and sustainable protocol to measure and handle these devices.

From the characterization side, we are exploring ways to work around the Maximum Power Point Tracking routine currently applied at ESTI [2], in order to optimize measurement time and measurement accuracy. The rationale behind it, is that the highly time consuming measurement procedure currently applied, is considered to not be feasible in the long term, as an accurate up-scaled screening protocol of PSC. From the recycling perspective instead, we concentrated on the glass substrate as the most promising and suitable component to recover, thanks to its high market value, strong physio-chemical stability and ease of processing. Compared to the common results reported so far in the specific literature of the field, which focused on the use of hazardous solvents like DMF, i here we report the use of acetone as a non-hazardous and inexpensive solvent to recover the substrate from PSC, thus potentially reducing the environmental impact of the whole process.

Results achieved at the JRC aim to contribute to the development of future policies regarding the large-scale implementation of PSC as high-efficiency and low-cost PVs.

[1] https://www.pv-magazine.com/2023/05/30/kaust-claims-33-7-efficiency-for-perovskite-silicon-tandem-solar-cell/

[2] Giorgio Bardizza et al 2021 J. Phys. Energy 3 021001

Perovskite solar cells (PSCs) are emerging as a cornerstone in the pursuit of efficient and sustainable solar energy. Their exceptional laboratory-scale performance has sparked considerable interest, yet transitioning these high-efficiency cells to scalable, commercial applications presents a myriad of challenges. Central to these challenges is the reliance on high-toxicity solvents, such as DMF/DMSO for the perovskite layer and Chlorobenzene/ Chloroform for the hole transporting layer (HTL). These substances, while effective in controlled settings, pose significant health and environmental hazards, particularly when considered for large-scale manufacturing. The exposure limits and handling complexities of such chemicals demand urgent attention and alternative solutions.

Moreover, the long-term stability of PSCs under real-world environmental conditions, especially humidity, has been a persistent obstacle. Despite their impressive initial performance, these cells often face degradation over time when exposed to varying humidity levels, questioning their practicality for long-term use. The current production methods and materials, optimized for highly efficient in PSCs, often result in increased production costs, making it challenging to compete with established solar technologies in the market.

In response to these limitations, our study delves into the development of roll-to-roll (R2R) coated perovskite solar cells including the top electrode using low-toxicity solvents, marking a significant shift from traditional methods. This approach not only seeks to reduce the ecological footprint of PSC production but also to enhance the safety and feasibility of large-scale manufacturing. We strategically replaced the conventional solvents with safer alternatives: DI water was used for the tin oxide layer, for the critical perovskite and hole transporting layers, we opted for Acetonitrile (ACN) and Oxylene, respectively, significantly mitigating the environmental and health hazards. Furthermore, 2-Methylanisole was chosen for the carbon ink, reinforcing our commitment to safer and much cheaper production processes.

The results of our approach showed that the R2R coated PSCs, incorporating carbon electrodes, not only achieved a power conversion efficiency (PCE) of over 10% but also demonstrated extraordinary stability (D1- ISOS). Unencapsulated devices maintained 85% of their initial PCE after 90 days, a testament to the durability that can be achieved alongside environmental consciousness.

These findings do more than just validate the effectiveness of low-toxicity solvents in the fabrication of PSCs. They represent a crucial advancement in making PSC technology a realistic, sustainable option for large-scale solar energy production. By addressing the pivotal issues of toxicity, stability, and cost, our study paves the way for PSCs to transition from laboratory breakthroughs to robust, environmentally responsible, and commercially viable energy solutions, setting a new precedent in the solar energy landscape.

Metal Halide perovskites have emerged as highly promising candidates for photovoltaics with the certified record power conversion efficiency (PCE) reaching 26.1% for single-junction perovskite solar cells (PSCs)1. However, to date, most of the reported highly efficient PSCs were obtained based on the regular n-i-p architectures at the laboratory scale, i.e., typically ~0.1 cm2 2-5, which are not suitable for upscaling. Inverted p-i-n cells, on the other hand, are attractive for upscaling due to their architecture simplicity at relatively low material cost and potentially high stability, however, their PCE still lags behind the n-i-p counterparts6,7. Therefore, our work has been focused on improving the efficiency of p-i-n cells and scaling them to produce efficient and stable modules. To push the PCE of cells, we developed a dual interface passivation strategy which led to a champion PCE of 24.3% for small-area cells and a champion PCE of 22.6% for a 3.63 cm2 mini-module. Next, we developed a bladed-coated interlayer to passivate the NiOx/perovskite interface. As a result, PCEs of 21.8% and 20.5% are demonstrated for cells of 0.13 cm2 and 1 cm2, respectively. The scalability of this p-i-n architecture is successfully demonstrated, achieving aperture area module efficiencies of 19.7%, 17.5%, and 15.5% for minimodules of 4 cm2, 16 cm2, and 100 cm2, respectively. Furthermore, we have upscaled up our baseline process and device stack to large-area modules. We fabricated bi-facial (781 cm2) perovskite solar modules exhibiting a power conversion efficiency of 16.3%, respectively. Moreover, the bi-facial mini-module retained ~ 92% of initial PCE after 1000 h of standard IEC 61215-based damp heat (85 °C, 85% relative humidity) test.

References

1NREL Best Research-Cell Efficiencies Chart. Accessed on May 10, 2023.

2 Min, H. et al. Perovskite solar cells with atomically coherent interlayers on SnO2 electrodes. Nature 598, 444–450 (2021).

3 Zhao, Y. et al. Inactive (PbI2)2RbCl stabilizes perovskite films for efficient solar cells. Science 377, 531–534 (2022).

4 Zhang, T. et al. Ion-modulated radical doping of spiro-OMeTAD for more efficient and stable perovskite solar cells. Science 377, 495–501 (2022).

5 Kim, M. et al. Conformal quantum dot–SnO2 layers as electron transporters for efficient perovskite solar cells. Science 375, 302–306 (2022).

6 Jiang, Q. et al., Surface reaction for efficient and stable inverted perovskite solar cells, Nature 611, 278–283 (2022).

7 Li, Z et al., Organometallic-functionalized interfaces for highly efficient inverted perovskite solar cells. Science 376, 416–420 (2022).

Vapor phase deposition of organic-inorganic perovskite solar cells is raising increasing interest in both academia and industry, holding great promise for the commercialization of perovskite-based photovoltaics. Despite the dominance of vapor phase deposition processes in commercial thin film manufacturing of photovoltaics and other optoelectronic applications, research on vapor phase processed PSCs is still underrepresented compared to their solution-based counterparts. Solution-processed PSCs still dominate the field, benefiting from fast optimization feedback and straightforward integration in modern research laboratories. This contribution will present a recent perspective that coveys a balanced viewpoint of industry and academics on the prospects of vapor phase deposition of perovskite photovoltaics. The perspective highlights strategic opportunities of vapor phase deposition for the commercialization of perovskite-based PV.  In addition, the latest developments at the Karlsruhe Institute of Technology on vapor phase deposited perovskite thin films for perovskite solar cells and perovskite/Si tandem solar cells will be presented.

The addition of a perovskite thin-film solar cell on the front side of a commercial silicon solar cell promises power conversion efficiencies beyond the theoretical efficiency limit of silicon photovoltaics, which sits at around 29.5%. Advantageously, the cost of adding this perovskite solar cell to form a tandem device should be diluted at the system level by balance-of-system components, making the approach attractive from a commercial perspective.

This contribution will review perovskite/silicon tandem solar cells developments ongoing at CSEM and EPFL PV-Lab, which closely collaborate on the topic. Focusing first on 1-cm² tandem solar cell prototypes, different approaches to reduce losses occurring at the interfaces of the perovskite top-cell absorber will be discussed. For example, the use of phosphonic acid compounds, as hole transport layer and as additive in the perovskite ink, has enabled the demonstration of tandem solar cells reaching certified power conversion efficiencies >30% with both planar and textured Si wafers.^1,2 Furthermore, the development of process flows compatible with industrial requirements will be discussed. Notably, a Ag paste screen-printing process compatible with the low thermal budget of the perovskite top cell has been developed, yielding for example 25-cm² tandem cells with a certified power conversion efficiency of 29.6%. Also, progress on perovskite absorber deposition processes compatible with larger, industrial-sized tandems (M6 and above, see Figure) will be discussed and challenges ahead highlighted. Finally, the presentation will review the results of various stability testing procedures, including damp heat, thermal cycling, light soaking and other accelerated aging conditions set up to reveal the failure modes of perovskite solar cells.³

Perovskite solar cells have been attracting increasing attention in recent years due to their rapid progress with record efficiency of 26.1% for single junction and 33.9% for tandem devices respectively [1]. The biggest concern that impedes the application of perovskites and poses tremendous challenges for their commercialization is their long-term stability under operation [2]. Even if now perovskites are passing standardized protocols (IEC 61215) and ISOS procedures, those tests cannot resemble the outdoor operational conditions with day-night cycles and continuous change in temperature and irradiance levels. Although outdoor stability testing has been reported for different types of perovskite devices so far [3], [4] there is still a lack of quantitatively precise information about the diurnal trend in long-term performance of perovskites under outdoor conditions.

In this work, several perovskite and perovskite on Silicon tandem mini-modules were extensively investigated outdoors at real environmental conditions for a duration of up to two years and indoors using a range of advanced optoelectronic methods to set-up a complete optical and electrical characterization of perovskite devices. Characterization methods of spatially - resolved Electroluminescence/Photoluminescence, Dark Lock-In Thermography, Raman and Ultrafast spectroscopies have been utilized for this purpose. Outdoor testing for several months in the field demonstrated the impact of irradiance and temperature on the major electrical parameters of the devices. Interplay of metastability and temperature effects were detected in the output power temperature coefficients results while agreement was found between indoor laboratory tests and outdoor results for voltage temperature coefficients.

Diurnal performance degradation and recovery overnight were calculated for the first time outdoors. Seasonality effects in the diurnal changes are discussed demonstrating the values of performance recovery overnight and diurnal performance degradation as well as the degradation-to-recovery ratio at different environmental conditions. The diurnal changes in performance, current and voltage have been calculated and facilitated on the understanding of irradiance effects on the major electrical parameters of the perovskite samples. A data-driven predictive model has been utilized for predicting the output power time-series of perovskites.

Moreover, several optoelectronic and spectroscopic methods such as Ultrafast and Raman spectroscopies and Dark Lock-In-Thermography methods have been employed to understand changes in carrier relaxation dynamics and chemical properties after outdoor exposure as well as hotspot evolution in the devices under test. Results demonstrated FA decomposition products and changes in carrier relaxation mechanisms in Raman and Ultrafast methods respectively. Finally, Dark Lock-In Thermography method revealed hotspot evolution in both perovskite active and interconnection areas of the cell.

Metal-halide perovskite (MHP) photovoltaic (PV) modules are progressing towards commercialization. One major hurdle that remains is establishing confidence in long-term field performance and durability of MHP modules. A lot of progress has been made in addressing many reliability issues in MHP cells and modules; however, there is still work to be done to understand degradation and demonstrate real world operation of this technology. In addition to establishing field performance and reliability, in the absence of established test protocols for MHPs, many reliability studies have been conducted using the International Electrotechnical Commissions 61215-series (IEC 61215) of standardized tests, which do not yet have specifications for MHP modules. While some of the existing IEC 61215 protocols may be partially relevant to degradation mechanisms incurred by MHPs, a set of testing protocols specifically relevant to this technology is likely needed to ensure that accelerated testing can accurately assess the reliability of MHPs.   Here, I will present a brief overview of an initial field demonstration of MHP modules as part of the Perovskite PV Accelerator for Commercializing Technologies, PACT, program. In addition, I will discuss accelerated testing results in the development of a test procedure for the qualification of commercial MHP modules. Particular attention will be given to light and elevated temperature testing, which has shown a particularly large impact on MHP performance but is not thoroughly covered in IEC 61215.

Degradation of perovskite solar cells (PSCs) is often the result of exposure to extrinsic environmental factors: humidity, oxygen, and thermal stress. However, intrinsic factors, notably ion migration, are also linked to stability issues, such as via lattice strain[1] or phase segregation[2,3]. Being intrinsic, these factors could limit stability and energy yield in commercial devices even if they manage to achieve excellent isolation from the atmosphere.

The most extreme conditions under which ion migration could trigger degradation is under day-night cycling, where swings in the PSC’s internal electric fields will trigger large shifts in the distribution of ionic defects in the perovskite absorber. This challenge is recognised by the proposed day-night cycling stability testing protocol presented in the consensus statement for perovskite solar cell stability testing[4].

In this context, our work assesses the extent of the stress placed on PSCs by day-night cycling, relative to more conventional maximum power point tracking. We consider the influence of the perovskite composition, notably the number of different A-site cations and X-site halides (Double and Triple). Simultaneous with the day-night cycling, we capture photoluminescence (PL) intensity images to determine the spatial homogeneity of the degradation triggered by the cycling effects, and thus whether the degradation mechanisms are intrinsic to the film or precipitated by initial regions of heterogeneity.

Our analysis focuses on an inverted ITO/PolyTPD/PFN-Br/Perovskite absorber/C60/BCP/Au structure, fabricated using an anti-solvent method. The perovskite composition was based on triple cation and triple halide. Moreover, to examine the effect of perovskite composition and film fabrication route, triple and double halide-based perovskite was further formulated with the anti-solvent and vacuum zig method.

References:

1.         Tsai, H. et al. Light-induced lattice expansion leads to high-efficiency perovskite solar cells. Science 360, 67–70 (2018).

2.         Duong, T. et al. Light and Electrically Induced Phase Segregation and Its Impact on the Stability of Quadruple Cation High Bandgap Perovskite Solar Cells. ACS Appl. Mater. Interfaces 9, 26859–26866 (2017).

3.         A. Jacobs, D. et al. Lateral ion migration accelerates degradation in halide perovskite devices. Energy Environ. Sci. 15, 5324–5339 (2022).

4.         Khenkin, M. V. et al. Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures. Nat. Energy 5, 35–49 (2020).

The scalable slot-die coating methods adopted within TNO enable fabrication of efficient single junction perovskite solar devices with intrinsic stability using various material and layer combinations. Furthermore, several different encapsulation strategies are investigated to define a low-cost route to guarantee long term stable modules. Demonstration of a stable opaque and semi-transparent bifacial flexible perovskite module is a step forward on various applications, such as building- and vehicle-integrated PV (BIPV & VIPV) and noise barriers on highways. In this talk, we will give an overview of our story towards realizing a stable, efficient, and bifacial perovskite processed via roll-to-roll slot-die coating technique.

As an outlook, we show recent work on realizing multi-junction perovskite solar cells and modules. Furthermore, we reveal a method how flexible modules may be integrated in bespoke photovoltaic modules as enabling process for integrated PV and an important step towards commercializing this emerging PV technology.

The graphical abstract shows an example of roll-to-roll coated perovskite.