Program

The industrialization of Perovskite Solar Cells (PSCs) can only be possible if device stability and module reliability is further enhanced. In this work, we present our most recent work related to the enhancement of perovskite solar cells stability. The studies were carried out following the ISOS protocols for dark storage (ISOS-D), indoor (ISOS-L) and outdoor (ISOS-O) ananlysis. We have modified the halide perovskite abdorber, the transport layers and the device interfaces via several methods such as additive engineering and the application of novel electron and hole transport layers (like MXenes, novel organic hole transport materials, etc). For example, we use the 2D Ti3C2 MXene in normal PSC configuration of the type: FTO / c-TiO2 / m-TiO2 / halide perovskite (HP) / MXene / Spiro-OMeTAD / Au. We enployed the quadruple halide perovskite (HP) Rb0.05Cs0.05MA0.15FA0.75Pb(I0.95Br0.05)3 as the absorber, and the MXene (Ti3C2-Tx) at the interface of HP and the hole transport layer (HTL) to fabricate HP/MXene heterojunctions. Our champion solar cells resulted in 21.95% PCE, in comparisson with the 20.56 % obtained for the referene PSC. Both indoor stability studies under ISOS-L protocol (continuous MPP tracking under N2 atmosphere for 1000 h) and outdoor stability analyses under the ISOS-O protocol (MPP tracking, encapsulated devices) demonstrated the superior stability of PSCs when the MXene is employed, especially under high humidity (60-85%) conditions where the PSCs showed excellent recovery after a rainy day. Thermal admittance spectroscopy (TAS) revealed that the use of MXene:H3pp results in the decrease of deep and shallow trap state densities. This report  provides pioneering study of additive engineering for adabtable bulk passivation and interface passivation through MXene nanosheets. Other examples include the application of novel organic HTL or the use of Machine Learning to understand the coorelation of indoor and outdoor stability.

[1] Kouroudis, I.; et al., Lira-Cantu, M.; Gagliardi, ACS Energy Letters 2024, 9 (4), 1581-1586,

[2] Karimipour, M.; et al., Lira-Cantu, M. Advanced Energy Materials 2023, 13 (44),

[3] Haibing Xie, et al., Monica Lira-Cantu. Joule, 5, 2021, 1-21.

[4] Khenkin, M.V., et al., Lira-Cantu, M. Click the link to open the URL in a new window." href="https://www.nature.com/nenergy" target="_blank" rel="noopener">Nature Energy 2020, 5, 35–49.

Outdoor stability testing under natural sunlight provides the most relevant test of solar cell stability under operational conditions.[1] Understanding perovskite-based solar cells’ recovery properties under natural diurnal light-dark cycling can point to methods to extend its lifetime.[2, 3] A broad range of lifetimes of encapsulated single-junction perovskite-based cells and modules at outdoor operation at MPP were previously published, and the variability may be attributed to different cell architectures but also to the climate conditions. We systematically studied the effect of climate conditions on outdoor operational lifetime of n-i-p PSCs, determined their lifetime indicators (T80 and T50) in different seasons, correlated them with the outdoor irradiance and temperatures, and simulated such conditions in indoor light cycling tests. Our results show that outdoor T80 is climate dependent hence it should not be used as a (comparative) cell stability indicator.[4] We further demonstrated that the outdoor degradation behavior of PSCs can be predicted from accelerated indoor stability analyses using machine learning algorithms and mathematical decompositions.[5] Understanding the effect of outdoor climate parameters will be combined with these algorithms to determine the most relevant stress factors affecting outdoor stability of perovskite solar cells.

1.            Solar RRL, 2020. 4(2): p. 1900335.

2.            Energy Environ. Sci., 2018. 11: p. 739-743.

3.            ACS Applied Energy Materials, 2018. 1(2): p. 799-806.

4.            in prep.

5.            ACS Energy Letters, 2024. 9(4): p. 1581-1586.

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.

The complex heterogeneity in perovskite-based solar cells has been successfully explored using advanced synchrotron-based techniques. Utilizing X-ray fluorescence (XRF), grazing-incidence small-angle X-ray scattering (GISAXS), and grazing-incidence wide-angle X-ray scattering (GIWAXS), new opportunities have emerged for a deeper understanding of local element distributions, morphology, and structural analysis in perovskite materials and their functional layers. The capability of acquiring data in very short times, down to milliseconds, opens exciting possibilities for in-situ and operando synchrotron-based studies. This enables the tailoring of contrast conditions, thereby allowing the probing of more complex evolutions in element distribution, morphologies, and structure during device fabrication and operation. Thanks to these advanced techniques, we have gained insights into proper morphology regulation and achieved highly efficient perovskite single-junction solar cells1. Additionally, the limiting factor of trace amounts of water in the raw synthesis materials affecting device performance was identified2. The phase segregation mechanism in wide-bandgap perovskite was revealed and subsequently suppressed3. Finally, we uncovered the atmosphere-dependent degradation mechanisms of perovskite solar cells under different conditions using synchrotron-based operando GIXS techniques4.

(1) Guo, R.; Wang, X.; Jia, X.; Guo, X.; Li, J.; Li, Z.; Sun, K.; Jiang, X.; Alvianto, E.; Shi, Z. Refining the Substrate Surface Morphology for Achieving Efficient Inverted Perovskite Solar Cells. Advanced Energy Materials 2023, 13 (43), 2302280.

(2) Guo, R.; Xiong, Q.; Ulatowski, A.; Li, S.; Ding, Z.; Xiao, T.; Liang, S.; Heger, J. E.; Guan, T.; Jiang, X.; Sun, K.; Reb, L. K.; Reus, M. A.; Chumakov, A.; Schwartzkopf, M.; Yuan, M.; Hou, Y.; Roth, S. V.; Herz, L. M.; Gao, P.; Müller-Buschbaum, P. Trace Water in Lead Iodide Affecting Perovskite Crystal Nucleation Limits the Performance of Perovskite Solar Cells. Advanced Materials 2024, 36 (7), 2310237. DOI: https://doi.org/10.1002/adma.202310237.

(3) Guo, X.; Jia, Z.; Liu, S.; Guo, R.; Jiang, F.; Shi, Y.; Dong, Z.; Luo, R.; Wang, Y.-D.; Shi, Z. Stabilizing efficient wide-bandgap perovskite in perovskite-organic tandem solar cells. Joule 2024.

(4) Guo, R.; Han, D.; Chen, W.; Dai, L.; Ji, K.; Xiong, Q.; Li, S.; Reb, L. K.; Scheel, M. A.; Pratap, S.; Li, N.; Yin, S.; Xiao, T.; Liang, S.; Oechsle, A. L.; Weindl, C. L.; Schwartzkopf, M.; Ebert, H.; Gao, P.; Wang, K.; Yuan, M.; Greenham, N. C.; Stranks, S. D.; Roth, S. V.; Friend, R. H.; Müller-Buschbaum, P. Degradation mechanisms of perovskite solar cells under vacuum and one atmosphere of nitrogen. Nature Energy 2021, 6 (10), 977-986. DOI: 10.1038/s41560-021-00912-8.

Metal halide perovskites are ionic conductors and can undergo oxidation and reduction.  Perovskite solar cells often contain metal electrodes that can be oxidized.  Redox reactions occur quite rapidly when the cells are operated in reverse bias, which can happen when a shaded cell is forced to match the current of illuminated cells that are connected in series.  Shunting typically occurs in reverse bias when silver electrodes are used, but not when transparent conducting oxides or carbon are used. Oxidation of iodide can result in loss of iodine from the perovskite layer, which can also reduce power conversion efficiency.  The talk will describe the electrochemical degradation and how feasible it is to protect different types of modules with bypass diodes.

It is important to minimize stress in perovskite films to prevent mechanical failure and migration of ions and moisture at grain boundaries.  All inorganic perovskites annealed at high temperature have the most stress.  This stress results in unusually large moisture uptake.

The unproven durability of perovskite photovoltaics (PVs) is likely to pose a significant technical hurdle in the path towards the widespread deployment of this burgeoning thin-film PV technology. The overall durability of perovskite PVs, which includes operational stability, is directly affected by the mechanical reliability of metal-halide perovskite materials, cells, and modules, but this connection has been largely overlooked. Thus, there is a sense of urgency for addressing the mechanical reliability issue comprehensively, and help perovskite PVs reach their full potential. This presents many challenges, but it also offers vast research opportunities for making meaningful progress towards more durable perovskite PVs. Here I will highlight the important challenges and opportunities, together with best practices, pertaining to the three key interrelated elements that determine the mechanical reliability of perovskite PVs: (i) driving stresses, (ii) mechanical properties, and (iii) mechanical failure. I will also present examples of approaches to mitigate failure and extend the durability of perovskite PVs.

With the increase of power conversion efficiency (PCE), the stability of organic solar cells becomes the biggest obstacle for their commercialization. Nanomorphology of the bulk-heterojunction layer (BHJ) plays an important role in determining the performance and stability of the cells. In addition to pure donor and acceptor phases, amorphous intermixing phases of the donor and acceptor molecules are also formed within the BHJ film. However, quantitatively determining the content and structure of the intermixing phase is quite challenging. In this presentation, we demonstrate a method to characterize the aggregation and composition of non-fullerene acceptors (NFA) in the intermixed phases. By measuring the absorption spectrum of the blend films with different NFA concentration, we found a red-shift of the maximum absorption wavelength with the increase of the NFA concentration, which is ascribed to the change of intermolecular interactions. With these results, we can identify the nanostructure of the BHJ films under different processing conditions, and the results are correlated to the device efficiencies. Also, we found that the structure of the intermixing amorphous phases is rather stable under light and thermal stress, demonstrating an excellent intrinsic stability of the organic solar cells.

In the domain of perovskite formulations, module architectures, and layer stacks, comparing performance stability data across literature presents a significant challenge. The adoption of ISOS protocols has initiated a consensus, with researchers increasingly performing and reporting similar tests. We propose a reproducible and scalable module fabrication process, an operationally stable perovskite formulation, and a photo and thermally stable layer stack, enabling reliable indoor/outdoor test correlations and outdoor operation across diverse climate zones. The robustness of this process is demonstrated by its consistent run-to-run reproducibility, establishing a foundation for equitable outdoor performance comparisons among samples. Outdoor stability testing for various perovskite devices, including single-junction cells, remains underreported [1-3]. Some investigations offer extensive datasets but limit measurements to cells [4-6], leading to conclusions influenced by small device areas and lack of interconnections. This work, focused on modules of various sizes, reveals our findings on the long-term (+ 3 years) outdoor behavior under different climate conditions. Data analysis establishes correlations between module performance and irradiance levels, temperatures, seasons, and climates. Our approach integrates a feedback loop based on in-lab characterization and outdoor results to enhance understanding and enable adjustments for prolonged lifetimes. Preliminary findings indicate a consistent burn-in period within the initial 3 months, resulting in a performance decline of approximately 30%, followed by stabilization. As the dataset extends through September, we anticipate gaining a nuanced understanding of module behavior, potentially leading to enhanced module versions. A perovskite performance time series will be implemented for samples tested over a year at different sites, using statistical and machine learning forecasting methods to demonstrate the expected lifetime of the modules at various locations.

Bibliography:

[1]N. T. P. Hartono et al., “Stability follows efficiency based on the analysis of a large perovskite solar cells ageing dataset,” Nat Commun, vol. 14, no. 1, Dec. 2023, doi: 10.1038/s41467-023-40585-3.

[2]V. Stoichkov, N. Bristow, J. Troughton, F. De Rossi, T. M. Watson, and J. Kettle, “Outdoor performance monitoring of perovskite solar cell mini-modules: Diurnal performance, observance of reversible degradation and variation with climatic performance,” Solar Energy, vol. 170, pp. 549–556, Aug. 2018, doi: 10.1016/j.solener.2018.05.086.

[3]T. J. Silverman et al., “Daily Performance Changes in Metal Halide Perovskite PV Modules,” IEEE J Photovolt, vol. 13, no. 5, pp. 740–742, Sep. 2023, doi: 10.1109/JPHOTOV.2023.3289576.

[4]M. Khenkin et al., “Light cycling as a key to understanding the outdoor behaviour of perovskite solar cells,” Energy Environ Sci, 2023, doi: 10.1039/d3ee03508e.

[5]X. Li et al., “Outdoor Performance and Stability under Elevated Temperatures and Long-Term Light Soaking of Triple-Layer Mesoporous Perovskite Photovoltaics,” Energy Technology, vol. 3, no. 6, pp. 551–555, Jun. 2015, doi: 10.1002/ente.201500045.

[6]M. Jošt et al., “Perovskite Solar Cells go Outdoors: Field Testing and Temperature Effects on Energy Yield,” Adv Energy Mater, vol. 10, no. 25, Jul. 2020, doi: 10.1002/aenm.202000454.

The rapid research and development of perovskite solar cell (PSC) for practical applications are driven by both global warming concerns and industrial demands.Due to the distinctive characteristics exhibited by PSC, such as hysteresis, establishing a universally standardized and rational evaluation process becomes challenging. In this study, we present an equipment system designed to address this challenge. Hysteresis in I-V measurements, caused by capacitance components in stacked PSC, can lead to overestimation or underestimation of the performance. PSC exhibiting hysteresis in the I-V curve manifests two distinct maximum power points in the forward and reverse I-V curves, which depend on the scan speed, starting point, and direction of the scan. By implementing Maximum Power Point Tracking (MPPT), the genuine maximum output power of PSC can be promptly determined. Our newly developed device enables simultaneous I-V tracing and MPPT for PSC, facilitating research and development. The system continuously plots the light intensity and temperature data alongside the maximum power point, allowing each sample to handle up to 10 V and 1 A capacity. The MPPT algorithm maintained sample at its maximum power point, ensuring efficient power generation. This MPPT-integrated PV power analysis system offers a comprehensive solution to the evaluation challenges faced in PSC research and development. It enables accurate and efficient assessment of PSC performance, contributing to the advancement of practical applications and standardization of evaluation methods.

The stability of organic solar cells (OSC) is determined not only by the layer stack or a proper sealing of the device, but also by the morphological stability of the photoactive layer. The latter can be compromised by changes within the spatial distribution of the electron donor and electron acceptor, the two primary constituents of organic solar cells. The degree of phase separation between the donor and acceptor domains in the so-called bulk heterojunction (BHJ) is a crucial factor to OSCs performance. As a result, several ways have been attempted to stabilize the donor-acceptor distribution. One approach is to use amphiphilic molecules to stabilize the interface between donor and acceptor domains. Toluene sulfonic acid (TSA) was utilized as an additive to modify the morphology of P3HT:PC₆₀BM and PM6:Y6 solar cells. Not only the stability was indeed enhanced under thermal stressing, but also the performance could be raised. Overall a promising approach to encounter morphological degradation.

Organic photovoltaic cells (OPVs) have reached power conversion efficiencies of >20.2%, with a path to soon exceeding 25%. Thus, the potential for serving as a significant renewable energy resource depends on whether the requirements of low cost, high efficiency and prolonged lifetime are simultaneously fulfilled. Even with the fulfillment of these properties, OPVs have to serve applications that are qualitatively different than those filled by the incumbent Si-based PV technology. An application where OPVs have a unique opportunity for ubiquitous deployment is in power generating windows since they can be semitransparent (ST) in the visible while strongly absorbing in the infrared.  In this talk, I will discuss strategies explored in our laboratory to fabricate ST-OPVs with transparencies approaching ~50% and efficiencies of 10% or higher for both window and agricultural applications. Further, I will describe structures that show extrapolated intrinsic lifetimes of >30 years[2] under accelerated laboratory aging conditions, and short cost payback times.[3] Approaches to scaling the devices into prototype modules whose performance is reduced by only 10% from discrete, small test cells will be described. We have explored the reliability of ST-OPVs in outdoor environments in Michigan. Lessons learned, and failure mechanisms discovered will be discussed in this talk relating to both ST-OPV and opaque devices.

[1]         Z. Zheng, J. Wang, P. Bi, J. Ren, Y. Wang, Y. Yang, X. Liu, S. Zhang, and J. Hou, "Tandem Organic Solar Cell with 20.2% Efficiency," Joule, 2021.

[2]         Y. Li, X. Huang, K. Ding, H. K. Sheriff, L. Ye, H. Liu, C.-Z. Li, H. Ade, and S. R. Forrest, "Non-fullerene acceptor organic photovoltaics with intrinsic operational lifetimes over 30 years," Nature communications, vol. 12, no. 1, pp. 1-9, 2021.

[3]         B. Lee, L. Lahann, Y. Li, and S. R. Forrest, "Cost estimates of production scale semitransparent organic photovoltaic modules for building integrated photovoltaics," Sustainable Energy & Fuels, vol. 4, no. 11, pp. 5765-5772, 2020.

Organic solar cells have recently reached power conversion efficiencies of over 19%, highlighting the stability as their last remaining weak point. Their organic nature makes them strongly influenced by stresses such as oxygen, light, heat and humidity, which can be commonly found in their working environment. 

Incorporation of stabilizing additives (antioxidants, radical scavengers, hydroperoxide decomposers, UV absorbers) in active layers of organic solar cells is an attractive approach for inhibiting degradation as it is both inexpensive and easily upscalable, and it does not introduce further complexity into the device architecture.

Here we present our recent results on long-term stability improvement using naturally occurring antioxidants, such as vitamin C and beta-carotene, that act as singlet oxygen quenchers and radical scavenging compounds, as well as explore the synergistic effects of such compounds on the mechanical properties. The reported results and methods indicate a desirable route for mitigating degradation in organic solar cells.

References

1. Atajanov R, Turkovic V et al.  The mechanisms of degradation and stabilization of high-performing non-fullerene acceptor based organic solar cells. (in preparation)

2. Balasubramanian S, Turkovic V et al. Vitamin C for Photo-Stable Non-fullerene-acceptor-Based Organic Solar Cells. ACS Appl Mater Interfaces 2021; dx.doi.org/10.1021/acsami.3c06321

3. Prete M, Turkovic V et al. Synergistic effect of carotenoid and silicone-based additives for photooxidatively stable organic solar cells with enhanced elasticity. J Mater Chem C 2021; dx.doi.org/10.1039/D1TC01544C 

4. Turkovic V et al. Biomimetic Approach to Inhibition of Photooxidation in Organic Solar Cells Using Beta-Carotene as an Additive. ACS Appl Mater Interfaces 2019; dx.doi.org/10.1021/acsami.9b13085

5. Bregnhøj M, Turkovic V et al. Oxygen-dependent photophysics and photochemistry of prototypical compounds for organic photovoltaics: inhibiting degradation initiated by singlet oxygen at a molecular level. Methods Appl Fluoresc 2019; dx.doi.org/10.1088/2050-6120/ab4edc

In this study, we present the fabrication, performance, and year-long outdoor stability assessment of one of the largest mesoscopic carbon-based perovskite solar modules (C-PSCs) reported to date, featuring an active area of 518 cm² and a geometric fill factor exceeding 80%. Our modules, fabricated using scalable and low-cost manufacturing techniques such as screen printing and mechanical scribing, achieved a peak PCE of 9.4% under 1 sun illumination. Despite the inherent complexity of fabricating large modules, we demonstrate that these C-PSCs retain 68% of their initial PCE after 12 months of outdoor testing in a temperate climate, with only moderate performance losses driven by temperature-induced degradation during warmer months. The study highlights the importance of encapsulation—a process still lacking standardisation across the field—and its role in mitigating moisture ingress and maintaining module integrity.

The modules were fabricated using a mesoscopic stack of screen-printed TiO₂, ZrO₂, and carbon layers, with mechanical scribing employed to achieve precise interconnects between cells. Encapsulation was performed using a polyurethane sheet and butyl rubber sealant, providing resistance to moisture ingress. However, uneven perovskite crystallization due to non-uniform annealing was identified as a key degradation pathway, alongside encapsulation-induced thermal stress during module sealing. To mitigate these effects, process optimisation focused on more consistent heat distribution and improved control over solvent removal during perovskite curing.

The simplicity and scalability of the manufacturing processes, including screen printing and mechanical scribing, enable these modules to be produced with minimal capital cost, making them highly accessible for large-scale deployment. This low-cost approach, combined with the inherent stability of carbon-based architectures, positions this technology as a viable solution for energy generation in diverse regions, including those with limited resources. By reducing the reliance on expensive materials and complex fabrication techniques, this structure has the potential to significantly lower the barriers to entry for solar energy production, contributing to the democratisation of energy and supporting global efforts to expand access to affordable, renewable power.

Metal halide perovskite films and devices are susceptible to degradation upon exposure to ambient, elevated temperature, illumination, and electrical bias. The degradation under illumination typically occurs due to electrochemical redox reactions initiated by photogenerated charge carriers. The oxidation of iodide and the generation of various oxidized species (interstitial iodide I_i, iodine I₂, triiodide I₃^-) starts a chain reaction of degradation since I₃^- can readily deprotonate organic cations such as methylammonium cation MA⁺ or formamidinium cation FA⁺.¹ While the electrochemical redox reactions are in principle reversible, the loss of volatile degradation products resulting from deprotonation of organic cations will cause irreversible degradation. The degradation processes in different environments are strongly dependent on the composition of the perovskite, as well as device architecture which affects the charge collection. Here we investigated the stability under illumination for three different perovskite compositions, namely commonly used CsFAMA mixed cation perovskite Cs_0.05(FA_0.87MA_0.13)Pb(I_0.87Br_0.13)₃,^2,3 low Br perovskite Cs_0.05(FA_0.98MA_0.02)Pb(I_0.98Br_0.02)₃,⁴ and MA-free perovskite Cs_0.1FA_0.9PbI_2.9Br_0.1.⁵ We have found that low-Br perovskite, while enabling high efficiency, exhibits poor stability with significant phase transformation to d-FAPbI₃ as well as decomposition to PbI₂ under a range of testing conditions. In comparison, CsFAMA films did not show the formation of d-FAPbI₃ phase, but demonstrated degradation to PbI₂. Among the three compositions considered, MA-free perovskite exhibited the best stability. In addition, surprisingly it exhibited higher sensitivity to exposure to moisture compared to oxygen under illumination. The stability of MA free perovskite could be significantly improved with additives, and the role of different additives in stability improvement is discussed.

Bibliography

1. J. N. Hu, Z. Xu, T. L. Murrey, I. Pelczer, A. Kahn, J. Schwartz, B. P. Rand, Adv. Mater. 2023, 35, 2303373.
2. M. Saliba, J. P. Correa-Baena, C. M. Wolff, M. Stolterfoht, N. Phung, S. Albrecht, D. Neher, A. Abate, Chem. Mater. 2018, 30, 4193−4201;
3. J. Y. Lin, Y. T. Wang, A. Khaleed, A. A. Syed, Y. L. He, C. C. S. Chan, Y. Li, K. Liu, G. Li, K. S. Wong, J. Popović, J. Fan, A. M. C. Ng, A. B. Djurišić,, ACS Appl. Mater. Interfaces 2023, 15, 24437-24447, 2023.
4. D. Li, Y. Huang, R. Ma, H. Liu, Q. Liang, Y. Han, Z. Ren, K. Liu, P. W. K. Fong, Z. Zhang, Q. Lian, X. Lu, C. Cheng, G. Li, Adv. Energy Mater. 2023, 13, 2204247.
5. Q. An, L. Vieler, K. P. Goetz, O. Telschow, Y. J. Hofstetter, R. Buschbeck, A. D. Taylor and Y. Vaynzof, Adv. Energy Sustainable Res., 2021, 2, 2100061.

Talk will provide an update on the NREL perspective on metal halide perovskite (MHP) based photovoltaics (PVs).  This will include an argument of why MHP-PV technologies are critical and how the need to develop these technologies drives research needs in stability and reliability.  Results from across multiple studies undertaken at NREL will be summarized to identify both technical success and failures or missed opportunities to advance the stability of MHP and MHP enabled PV technologies.  Connections to device efficiency and manufacturing which are intimately linked to stability and reliability will also be highlighted.

Perovskite solar cells (PSCs) are rapidly gaining recognition as a promising photovoltaic technology, achieving a power conversion efficiency (PCE) of 26.1% [1]. As a potential alternative to traditional silicon cells, PSCs offer unique advantages but are hindered by significant stability challenges that affect their longevity. This research specifically investigates the stability and degradation mechanisms of semitransparent PSCs, leveraging their dual-sided measurement capability to quantitatively analyze recombination and transport mechanisms through electrical modeling [2].  The study employed semitransparent samples in an inverted architecture, incorporating a CH₃NH₃PbI₃ absorber layer. The focus was on detailed assessment of degradation under dark conditions (ISOS-D), continuous light illumination (ISOS-L) and in outdoor conditions (ISOS-O), while tracking changes in critical photovoltaic parameters such as PCE, fill factor (FF), open-circuit voltage (V_oc), and short-circuit current density (J_sc) [3]. By employing modulation light intensity techniques and drift-diffusion modeling, we analyzed the principal internal degradation mechanisms. This analysis primarily targeted the recombination and transport processes occurring within the perovskite bulk and at interfaces between the hole transport layer/perovskite and perovskite/electron transport layer. The results from these studies highlighted consistent degradation patterns, providing a crucial foundation for defining optimization strategies in future research to enhance the stability of PSCs. These findings highlight the critical need for more in-depth investigation into the degradation processes occurring in PSCs throughout their operational lifetime. This research establishes a solid foundation for strategic enhancements in PSC design, specifically aimed at minimizing internal degradation and extending the durability and efficiency of these solar cells.

Bibliography

[1] National Renewable Energy Laboratory (NREL), Chart of Best Research-Cell Efficiencies

[2] D. Glowienka, Y. Galagan, Advanced Materials 34 (2022) 2, 2105920

[3] M. Khenkin et al., Nature Energy 5 (2020) 35–49

Organic semiconductors are an emerging class of materials with various optoelectronic applications. The high commercialisation potential of this technology is evidenced by a few companies that have already launched their products into the market or are working towards this goal.

In my talk, I will introduce sustainable routes to manufacture solution-processed organic photovoltaics. One current limitation of this technology,  is the use of not eco-friendly solvents and materials during the device development stages. Most organic electronic devices require halogenated and non-halogenated aromatic solvents during their fabrication. For large-scale production and further commercialisation, this is a key limitation. This arises from the fact that organic semiconductors are highly soluble in this category of solvents, which are often carcinogenic or toxic to the human reproductive systems and negatively impact the environment. Here, we will show high-performing organic solar cells developed from novel, more sustainable organic semiconductors (in terms of less waste during synthesis and less energy consumption) as well as eco-friendly solvents. In particular, solvents derived from biomass have been explored for their application in delivering high-performing organic photovoltaics based on PTQ10:Y12 and FO6-T:Y12 with PCE > 14%.¹

In addition, I will discuss possible degradation mechanisms of the bulk heterojunction systems containing Y6 or Y12 as the acceptor, after degradation with indoor and outdoor light. A series of results will be discussed, for example, combining Suns-Voc temperature-dependent J-V measurements, AFM, and EPR in order to estimate the shape of DOS and the degradation mechanisms.

References

1.        Panidi, J., Mazzolini, E., Eisner, F., Fu, Y., Furlan, F., Qiao, Z., Rimmele, M., Li, Z., Lu, X., Nelson, J., et al. (2023). Biorenewable Solvents for High-Performance Organic Solar Cells. ACS Energy Lett 8, 3038–3047. https://doi.org/10.1021/ACSENERGYLETT.3C00891.

Cesium Formamidinium Lead halide (CsFA) is one of the promising perovskites from high performance and stability^1,2 standpoint. However, works on fabricating this CsFA perovskite in relatively high humidity level, especially with carbon electrodes for economical reasons and ease of scaling up are still scarce. In this talk, I will present an environmentally friendly approach to fabricate high-quality perovskite via gas-quenching of urea-perovskite precursor in 40% RH humidity condition. This recipe lengthens annealing window and yield perovskite with 1 micrometers grain size with high compactness³. Additionally, we showcase various surface defect passivation, especially organic molecules and polymers to not only improve the efficiency and stability of perovskite solar cells⁴ but also enable ambient fabrication of hole transport layer alternatives to Spiro-OMETAD. This includes ambient fabrication of Copper(I) thiocyanate and its solvent modification to improve their stability. Additionally, development of transferable carbon electrode will be discussed to complete the full PSCs totally in ambient.

References

1.      R. Cheacharoen, N. Rolston, D. Harwood, K.A. Bush, R.H. Dauskardt, M.D. McGehee*, “Design and understanding of encapsulated perovskite solar cells to withstand temperature cycling”, Energy & Environmental Science, 11, 144-150 (2018).

2.      R. Cheacharoen, C.C. Boyd, G.F. Burkhard, T. Leijtens, J.A. Raiford, K.A. Bush, S.F. Bent, M.D. McGehee*, “Encapsulating perovskite solar cells to withstand damp heat and thermal cycling”, Sustainable Energy & Fuels, 2, 2398-2406 (2018).

3.      C. Harnmanasvate, R. Chanajaree, N. Rujisamphan, Y. Rong, R. Cheacharoen*, “Ambient Gas-Quenching Fabrication of MA-Free Perovskite Solar Cells Enabled by an Eco-Friendly Urea Additive”, ACS Applied Energy Materials, 6,20, 10665-10673 (2023)

4.      M.Hu, Y. Zhu, Z. Zhou, M. Hao, C. Harnmanasvate, J.Waiyawat, Y. Wang, J. Lu, Q. An, X. Li, T. Zhang, Y. Zhou*, R. Cheacharoen*, Y. Rong*, “Post‐Treatment of Metal Halide Perovskites: From Morphology Control, Defect Passivation to Band Alignment and Construction of Heterostructures”, Advanced Energy Materials, 2301888 (2023)

Solar photovoltaic (PV) technology, a cornerstone in global efforts to mitigate CO2 emissions, faces an ambitious target. Projections suggest that the global PV generating capacity should reach approximately 70 terawatts (TW) by 2050. This rapid transition to renewable energy sources within a feasible timeframe necessitates an average installation of 6-10 kilowatts (kW) of PV per capita and an annual production output of 3-4 TW. Silicon-based PV technologies dominate the market landscape, offering a robust supply chain, well-established manufacturing processes, and competitive levelized cost of electricity (LCOE) metrics. However, a critical challenge persists: how can we enhance the power conversion efficiency (PCE) of PV systems without compromising their cost-effectiveness?
The concept of tandem solar cells has long been explored as a pathway to improve efficiency. Tandem cells stack two distinct cells atop each other, each optimized to capture complementary segments of the solar spectrum. Silicon-perovskite tandems hold significant promise. Combining silicon's maturity with perovskite's potential for rapid efficiency improvements, these tandems offer a compelling solution to accelerate progress in addressing climate change while bolstering the silicon market. This review delves into the most promising pathways for integrating perovskite-based PV technologies into industrial settings. Emphasizing non-concentrated tandem designs, the focus lies on configurations that promise efficiency gains without significant increases in system costs. These configurations typically involve pairing inexpensive solar absorbers with different bandgaps to optimize sunlight absorption across the spectrum. While several challenges exist in realizing these configurations, particularly regarding processing  techniques, strategic decisions remain nebulous. In navigating these challenges, the manuscript highlights the potential of slot-die coating as a pivotal fabrication technique. With its scalability, potential for short cycle times, and ease of processing, slot-die coating is positioned as a strategic choice for advancing perovskite-based PV technology. By elucidating the evolving landscape of performance-size relationships, this review underscores the crucial role of slot-die coating in facilitating the rapid integration of perovskite-based PV systems into mainstream industrial applications.

Although perovskite solar cells (PSCs) have reached impressive efficiencies [1], stability remains an issue in view of the necessary lifetimes. Degradation as result of partial shading has been identified as one of the great hurdles impeding commercialization of the single-junction perovskite solar cell [2]. Here, we are investigating the impact of low-intensity illumination on the reverse bias behavior of perovskite solar cells. This imitates the situation in a module that is partially shaded by an object at a distance, enabling illumination by diffuse light, and in bifacial modules that might receive diffuse illumination from their back side, even in the case of absolute shading.

To that end, we fabricated semi-transparent perovskite solar cells and performed voltage sweeps far into the reverse bias regime in the dark, and under illumination by a white LED from each side. Then, we determined the breakdown voltages as defined by Bowring et al. as the voltage at which -1 mA/cm2 flows [3], correcting for the light-generated current. We related the shift of the breakdown voltage with regard to the breakdown voltage in the dark to the illumination intensity, using the Jsc as measure (see Figure 1).

We observe a steep shift in the breakdown voltage at very low light-intensities and a levelling off below 0.1 sun. While we are still investigating possible mechanisms, consequences for modules are already conceivable. Small spatial variations in shading could lead to significant spatial variations in breakdown voltage. The regions with smaller breakdown voltage would then pass most of the current, accompanied by high local current densities, and followed by strong local degradation. Locally irreversibly damaged cells would reduce the power output of the whole module and, in the worst case, force the affected cell into reverse bias even outside of shading events [4].

Bibliography

[1] Green, M. A., Dunlop, E. D., Yoshita, M., Kopidakis, N., Bothe, K., Siefer, G., & Hao, X. (2024). Solar cell efficiency tables (Version 63). Progress in Photovoltaics: Research and Applications, 32(1), 3–13. https://doi.org/10.1002/pip.3750.

[2] Lan, D., & Green, M. A. (2022). Combatting temperature and reverse-bias challenges facing perovskite solar cells. Joule, 6(8), 1782–1797. https://doi.org/10.1016/j.joule.2022.06.014.

[3] Bowring, A. R., Bertoluzzi, L., O’Regan, B. C., & McGehee, M. D. (2018). Reverse Bias Behavior of Halide Perovskite Solar Cells. Advanced Energy Materials, 8(8), 1702365. https://doi.org/10.1002/aenm.201702365.

[4] Qian, J., Ernst, M., Walter, D., Mahmud, M. A., Hacke, P., Weber, K., Al-Jassim, M., & Blakers, A. (2020). Destructive reverse bias pinning in perovskite/silicon tandem solar modules caused by perovskite hysteresis under dynamic shading. Sustainable Energy and Fuels, 4(8), 4067–4075. https://doi.org/10.1039/c9se01246j.

Perovskite technologies have advanced significantly in the past decade, transitioning rapidly from fundamental research to device engineering. The use of thin, flexible substrates in perovskite solar cells (PSCs) offers an exceptional power-to-weight ratio compared to traditional photovoltaic systems, enabling new applications in building-integrated and building-applied photovoltaics  (BIPV, BAPV) and the Internet of Things (IoT). This talk summarizes the recent progress in perovskite solar technologies on flexible substrates, focusing on the challenges encountered during their development. Understanding the mechanisms that limit the efficiency of flexible substrates compared to rigid ones is essential. This requires a detailed investigation into material science to identify and mitigate these limiting factors. Furthermore, challenges related to the upscaling of flexible substrates need to be addressed, including maintaining uniform layer deposition and minimizing defects such as pinholes. An overview of stability tests on flexible modules will be provided, suggesting common standard procedures and guidelines.1 These tests reveal additional issues that flexible modules face upon bending and how to prevent device degradation through ad-hoc encapsulation strategies. Recent advancements in flexible devices in the perovskite market will also be discussed. These include improvements in encapsulation techniques to enhance durability and performance under mechanical stress. For instance, our approach will be presented introducing bifunctional ligands, elastomers and cross linking molecules in the perovskite ink that improves grain boundary passivation and reduces cracking during bending, thus enhancing the mechanical stability of flexible PSCs. In conclusion, while significant progress has been made, several challenges remain that need attention from stakeholders to fully exploit the potential of flexible perovskite solar technologies. Addressing these challenges is crucial for the technology's commercialization and widespread adoption.

Bibliography

1. L. A. Castriotta et al.; Advanced Materials, submitted.

Research on materials and novel solar technology devices require detailed characterization of electrical properties under illumination. Testing of device stability requires testing for extended periods of time under controlled conditions while monitoring progress and change. Analysis of electrical and optical responses require flexibility in the experimental setup. infinityPV offers a range of multichannel maximum power point tracking source measure units for low and medium power 0.1-5 watts that can be coupled with novel LED based light sources that cover from 375 nm to 1900 nm in 64 wavelength intervals with the possibility for moderate solar concentration enabling many degradation experiments to be carried out. This can be coupled to laser beam induced current (LBIC) mapping which provides detailed insight into failure modes during degradation and insight into remnants of the processing paths. The new instruments and their capabilities will be briefly presented in this short company presentation.

Bibliography

infinityPV.com

The commercialization of perovskite solar cells (PSC) in the renewable energy sector is limited by it’s long-term stability. In this work, we critically assess how material stoichiometry and surface morphology affects the long-term stability of caesium-formamidinium-based PSC. We demonstrate that the variation in the perovskite precursor - lead iodide (PbI2) to formamidinium iodide (FAI) ratio influences the stability under various stress conditions (elevated temperature and light). A high molar ratio (PbI2/FAI >1.1) in the perovskite precursor results in a higher open-circuit voltage (VOC) and hence better power conversion efficiency (PCE). However, the quenching techniques (anti-solvent or vacuum quenching) during the processing do not affect the long-term stability of PSCs. Under ISOS-D2 (dark, 85 °C, intermittent current density-voltage J-V characterization) condition, the devices implementing a non-standard PbI2/FAI ratio (>1.1 or <1.1) exhibit degradation of the perovskite layer or it’s interfaces with the charge transport layers, leading to a decrease in performance over a period of 500 h. When tested under ISOS-L1 (100 mW/cm2, 25 °C, maximum power point tracking) condition, the devices with PbI2/FAI ≤1.1 remain stable whereas devices with PbI2/FAI >1.1 show a drastic drop in J over 500 h. A contradictory trend is observed in post-degradation analysis of devices stressed under ISOS-L1. The devices with PbI2/FAI ≤1.1 are stable under stress but their PCEs decrease during storage in dark as characterized by intermittent J-V. Migration of iodide ions (I-) to the electron transport layer and iodide vacancies (VI-) to the hole transport layer1 causes formation of shunts resulting in non-radiative recombination during storage in the dark. This work emphasizes the importance of post-degradation and dark recovery analysis of PSCs to understand a process as complex as perovskite instability under different stress conditions2.

Bibliography:

(1) Thiesbrummel, J.; Shah, S.; Gutierrez-Partida, E.; Zu, F.; Peña-Camargo, F.; Zeiske, S.; Diekmann, J.; Ye, F.; Peters, K. P.; Brinkmann, K. O.; Caprioglio, P.; Dasgupta, A.; Seo, S.; Adeleye, F. A.; Warby, J.; Jeangros, Q.; Lang, F.; Zhang, S.; Albrecht, S.; Riedl, T.; Armin, A.; Neher, D.; Koch, N.; Wu, Y.; Le Corre, V. M.; Snaith, H.; Stolterfoht, M. Ion-Induced Field Screening as a Dominant Factor in Perovskite Solar Cell Operational Stability. Nat. Energy 2024, 1–13. https://doi.org/10.1038/s41560-024-01487-w.

(2) Singh, R.; Hu, H.; Feeney, T.; Diercks, A.; Laufer, F.; Li, Y.; Duong, T.; Schackmar, F.; Nejand, B. A.; Paetzold, U. W. Danger in the Dark: Stability of Perovskite Solar Cells with Varied Stoichiometries and Morphologies Stressed at Various Conditions. ACS Appl. Mater. Interfaces 2024, 16 (21), 27450–27462. https://doi.org/https://doi.org/10.1021/acsami.4c04350.

Perovskite solar cells (PSCs) have emerged as promising candidates for next-generation photovoltaics due to their high efficiency and cost-effective fabrication. However, the long-term stability of PSCs remains a critical roadblock that must be addressed for their commercial viability. In this study we present recent results from our comparative stability analysis of PSCs under indoor, outdoor, and quasi-in-situ conditions. From indoor stability tests, we highlight performance declines primarily due to intrinsic material degradation and interfacial reactions while outdoor tests demonstrate the impact of environmental stressors as well as the importance of proper device encapsulation. We show that gases released from some encapsulation epoxies react with the PSCs, leading to faster degradation. Combining ISOS-L2I tests with electrochemical impedance spectroscopy in quasi-in-situ analyses, we highlight the roles of ion migration on various performance parameters. These findings underscore the importance of multi-faceted testing approaches to accurately predict the operational lifespan of PSCs and inform the development of more robust, stable devices for real-world applications.

Bibliography:

1. Feng, S.-P., et al., Roadmap on commercialization of metal halide perovskite photovoltaics. Journal of Physics: Materials, 2023. 6(3): p. 032501.

2. Karimipour, M., et al., Functionalized MXene/halide perovskite heterojunctions for perovskite solar cells stable under real outdoor conditions. Advanced Energy Materials, 2023. 13(44): p. 2301959.

3. Kouroudis, I., et al., Artificial Intelligence-Based, Wavelet-Aided Prediction of Long-Term Outdoor Performance of Perovskite Solar Cells. ACS Energy Letters, 2024. 9(4): p. 1581-1586.

The stability of organic solar cells (OSC) is strongly affected by the morphology of the photoactive layers, whose separated crystalline and/or amorphous phases are kinetically quenched far from their thermodynamic equilibrium during the production process. The evolution of these structures during the lifetime of the cell remains poorly understood. In this talk, we will show how the bulk-heterojunction (BHJ) morphology evolution under thermal loading of OSC can be simulated, using a recently developed phase-field (PF) model1. For the first time, this allows to investigate the interplay between all the potentially relevant physical processes (nucleation, growth, grain coarsening, amorphous phase separation, composition-dependent kinetic properties), within a single coherent framework.

It will be shown, in the general case, how the morphology evolution depend on the thermodynamic and kinetic properties of the donor acceptor blend2 3 4. The possible crystallization pathways and associated morphologies will be discussed in detail. Moreover, the approach will be applied to two real material system. In the first case, the evolution of the considered all-small molecule BHJ is relatively simple. The simulation results show unambiguously that it is driven only by crystals stability and growth. In the second case, the polymer-small molecule BHJ is very unstable. Its evolution is the result of a subtle interplay between amorphous phase separation and acceptor crystallization. In both cases, the simulation results are in very nice agreement with the experimental findings.

Overall, this contribution illustrates how advanced simulations can help understanding intrinsic stability, thus accelerating the development of 3rd generation photovoltaics and contribute to the energy transition.

Bibliography

1 Ronsin O.J.J.; Harting J., Advanced Theory and Simulations 2022, 2200286

2 Ronsin O.J.J., Harting J., Energy Technol. 2020, 8, 1901468

3 Ronsin O.J.J.; Harting J., ACS Appl. Mater. Interfaces 2022, 14, 49785

4 Siber M., Ronsin O.J.J., Harting J., J. of Mat. Chem. C 2023, 11, 15979

Both performance loss and degradation of perovskite solar cells (PSCs) are initiated at grain boundaries (GBs) and interfaces, where defects and mobile ions tend to accumulate under external stress, such as continuous illumination, humid environment, and elevated temperature. Therefore, suppressing surface defects along with inhibiting mobile ion migration is critical to achieve PSCs long term stability. Different molecular species have been explored to suppress defect formation and ion migration either in the perovskite bulk or at the adjacent interfaces, with the ultimate goal of achieving stable PSCs. These species include ammonium-based salts, small organic molecules, polymers and other passivation agents including inorganic salts. A new category of aprotic sulfonium-based molecules shows great potential in stabilizing PSCs, however, it remains largely unexplored. In this work, we innovated a sulfonium-based molecule to post-treat formamidinium lead iodide perovskite films, which shows outstanding stability upon light soaking and remarkably remains in black-phase after 2 years ageing under ambient condition without encapsulation. The DMPESI-treated PSCs deliver a breakthrough record in  operational stability of highly-efficient PSCs with less than 1% performance loss after more than 4500 h at maximum power point tracking, yielding a theoretical T80 of over 9 years under continuous 1-sun illumination. They also present less than 5% PCE drops under various ageing conditions.

Reference:
Suo, J., Yang, B., Mosconi, E., Hagfeldt, A., et al. Multifunctional sulfonium-based treatment for perovskite
solar cells with less than 1% efficiency loss over 4,500-h operational stability tests. Nature Energy, 9, 172-183  (2024).

Perovskites are thriving to enter the PV market with very high efficiencies and the potential for low production costs. However, stability concerns are currently the major show stopper for a successful market entry, as competitive Si solar modules last in the field for 25 30 years. Understanding the main intrinsic thermodynamic process es and limitations involved in the phase stability and decomposition kinetics is therefore of foremost interest to the whole perovskite research community. While there is a large amount of different studies investigating the effect of moisture and oxygen on device stability, these two stress factors can in principle be avoided by an ideal encapsulation of the devices. However, the thermal load to which perovskites will be exposed in solar modules (easily operating at elevated temperatures >80ºC in hot climates) is unavoidable. Interestingly, the data on the intrinsic thermodynamic stability of different perovskite phases is scarce and scattered, making a thorough comparison of the thermal (in)stability of perovskites and the underlying physical properties governing the decomposition a difficult task.

A systematic investigation i s therefore required and presented in this contribution. We base our analysis on the investigation of co evaporated ABX 3 perovskite thin films with the compositional variations along the A=MA,FA,Cs, B= Pb,Sn, Ag/Bi, X= I,Br,Cl] axes. These films have been evaporated in vacuum, and their phase evolution is analyzed via in situ X ray diffraction (ISXRD) upon thermal annealing inside the deposition chamber, i.e. without any exposure to air/moisture. The ISXRD allows to detect and monitor the crystallization process, the phase evolution and decomposition processes of the thin films during deposition and degradation . Isothermal and ramping experiments are used to determine decomposition kinetics and decomposition temperature s for the set of investigated perovskite compositions. The results are reviewed and compared under thermodynamic considerations, establishing a more general framework the intrinsic thermal (in)stability of halide perovskites.

For serious upscaling of stable perovskite solar cells, control over the quality of the perovskite material is most critical. A key challenge both for efficiency and stability is the controlled growth of perovskite crystallites. To this end, the underlying mechanisms that govern the crystallization process are still subject to a vigorous debate. A frequently cited theory is that the nuclei for the perovskite crystallization evolve from intermediate solvate clusters that might form colloids that act as seeds.[1,2] As of yet, however, insights that unambiguously link the complex formation in the precursor inks to the perovskite formation are lacking.

In this work we propose an alternative hypothesis and explain, why solid predictions based on nucleation are hard if not impossible. We begin our study with the additive thiourea, which we have use successfully in the past.[3,4] Specifically, we probe the precursor stage and transition over in-situ investigations during thin film deposition to the final films and their implementation into perovskite solar cells. While we confirm reports on colloidal lead-complexes in the precursor ink, that grow in size with increasing concentration, we observe, that modification of the lead complex formation or a retardation of the nucleation process might not be the dominant mechanism. We show, that the key impact of Thiourea and other popular additives unfolds during the annealing step, when solvent removal, nucleation and initial perovskite crystallization is already finished. We alternatively suspect a coarsening process limited by the species mobility. We substantiate the general validity of our insights for various iodine-based perovskite compositions and several popular additives. Hereby we find the proposed mechanism to be not only viable to explain the effect of additives, but also transferable to several post-processing approaches like thermal hot-pressing, where the mobility of the constituents is manipulated by other means.

Bibliography:

[1] Ahlawat P, et al. Chem. Mater. 32, 529 (2020).

[2] Flatken MA, et al. J. Mater. Chem. A 9, 13477 (2021)

[3] Brinkmann et al. Nature 604, 280 (2022)

[4] Brinkmann et al. ACS Appl. Mater. & Interf. 11, 40172 (2019)

With the practical application of organic solar cells, the ISOS protocol was launched as a guideline for evaluating stability under appropriate environmental conditions. The protocol includes the following test items in addition to the combination of four stress factors and their variations: ISOS-D (dark-storage/shelf-life), ISOS-L (light-soaking), ISOS-O (outdoor testing), ISOS-T (thermal cycling), and ISOS-LT (light-humidity-thermal cycling).

In order to differentiate organic solar cells from conventional crystalline silicon solar cells, various applications are being expanded. The power generation behavior under light intensity weaker than 1 Sun (100mW/cm²), which has been used as the "standard condition (STC)" until now, has become important, particularly for indoor light.

In this study, we first developed an ultra-precise LED solar simulator to understand the accurate power generation characteristics under low-illumination environments. We also present the results of comparing the performance evaluation of various solar cells using a maximum power point tracker (MPPT) capable of tracking picoampere currents.

Bibliography

1) L. Cojocaru, S. Uchida, P.V.V. Jayaweera, S. Kaneko, J. Nakazaki, T. Kubo and H. Segawa Scientific Reports, 7, 11790 (2017).

2) IEC/TC82 Technical Specification, “Guidelines for current-voltage measurements of metastable photovoltaic devices”, NP proposal 82/2216/NP (2023).

The performance of perovskite solar cells suffers from slow transients, some of them being partially reversible. A major origin is ion migration changing the electric potential distribution in the layers and triggering further electrochemical processes. In this talk, transient changes in the open-circuit voltage under illumination are correlated to electroluminescence measurements under continuously applied forward voltage. Solar cells under investigation are devices with mesoporous oxide scaffolds and carbon electrode; an architecture, which is supposed to be a potential solution for a fully printable and stable perovskite single-junction solar cell. It is found that the transients and degradation phenomena happening under forward bias share the same origin as under open circuit. Using device simulations and temperature-dependent measurements, it is concluded that the observations can be explained by slow mobile ionic species and an increased concentration of ions during ageing. Along with the changes of the open-circuit voltage, which commonly increases, a strong decrease in the current density is observed, which is further analyzed using spectrally resolved measurements.

Perovskite-based multi-junction solar cells demonstrate promising potential and offer a solution to overcome theoretical limits of single-junction cells by reducing thermalization losses. Although notable efficiencies are already achieved by emerging perovskite/silicon and all-perovskite tandem devices, significant challenges persist, including the substantial carbon emissions due to energy-intensive silicon wafer production or fundamental stability concerns due to the oxidation of Sn2+ to Sn4+ in narrow-gap perovskites. Solution-processed narrow-gap non-fullerene acceptor (NFA) organic solar cells (OSCs) circumvent these issues and present a compelling choice as rear cells in perovskite-based tandem devices. In our previous work, the benchmark PM6:Y6:PC61BM ternary OSCs maintained approximately 95% of its efficiency after 5000 hours of continuous operation under irradiation with low-energy photons (l = 850 nm), but it degraded rapidly when illuminated with a white light-emitting diode (LED), indicating that the visible spectral region is responsible for device degradation.[1] In a perovskite-organic tandem solar cell, the wide bandgap perovskite sub-cell serves as a low-pass filter that protects the organic sub-cell against high-energy photons.[2] While the photostability of the perovskite-organic tandem devices is still limited by the photostability of the wide gap perovskite, for the narrow gap subcell, NFA based organic solar cells might be a better choice compared to narrow-gap Pb-Sn perovskite solar cells.

   In this work we generalize our study to include a wider range of Y-type acceptors with various energy gaps (Y18 (Eg = 1.31 eV), CH1007 (Eg = 1.30 eV), mBzS-4F (Eg = 1.25 eV)), that we identified to show great promise in tandem operation by showcasing efficiencies > 23%, currently the highest values reported for perovskite-organic tandem solar cells with each respective NFA. Most importantly, we could evidence that the remarkable photostability found for the Y6 NFA is possibly generally valid for the whole Y-family, indicating that the introduction of Y-type NFA could bring about efficient and photo-stable prospects for perovskite-organic tandem technology. On the path to further explore the photostability of NFA based ternary OSCs in more detail, we utilize monochromatic LED sources covering the ultraviolet, visible, and near-infrared spectral regions. Our results reveal that under continuous operation in the maximum-power point under irradiation with low-energy photons (λ > 590 nm), the devices show excellent long-term stability (> 1000 hours), while higher-energy photons (λ < 530 nm) infer degradation. Combining this wavelength-selective degradation studies with in-situ photoluminescence, Raman spectroscopy and photoluminescence quantum yield investigations, we systematically investigate the distinct contributions of the donor polymer and the Y-type NFA along with possible degradation pathways in both cases. Hereby we also identify the degradation threshold energies of each constituent – an information that is not only crucial for the design of tandem solar cells, but also might provide the lever to design photo-stable single junction organic NFA-based solar cells. 

Bibliography

[1] Nature 2022, 604, 280-286.
 [2] Nature Reviews Materials 2024, 9, 202-217. 

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, perovskite solar cells undergo extensive degradation recovery during the resting time in dark and complex transient dynamics during the relatively short illumination time they experience in day-night cycling. Therefore, an ageing protocol based on continuous illumination will fail to quantitatively predict 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 with controlled temperature and illumination conditions allow a predictive analysis. We reported accelerated degradation of perovskite solar cells up to 60 times, i.e. five months of indoor testing could reproduce the standard 25 years of outdoor functioning. Our ageing protocol based on light/dark cycling will speed up perovskite solar cells' stability and commercialisation.

Flexible perovskite solar cells (f-PSCs) have recently reached power conversion efficiency (PCE) as high as 25.09 % [1] which is reaching their rigid counterparts on glass, which in very short time have achieved 26.1% of certified efficiency. The use of flexible substrates however, thanks to the high power/to weight ratio generated which is the range of 29.4 W/g compared to 8.31 W/g for amorphous silicon and 0.254 W/g for ultra-thin CdS / CdTe [2-3], opens up to a wide range of applications, from sensors for the Internet of Things, to the retrofitting of existing buildings to improve their energy efficiency (building-applied PV), to space.

In this context, sustainability of the fabrication process and stability of the devices are among the major issues to tackle. In this talk we will give an overview on different strategies that can be used to increase the overall sustainability of the fabrication process of perovskite solar cells including the use of green solvents for perovskite deposition and of hole transporting layers synthetized with low environmental impact approaches, the substitution of gold metallic contact with carbon. In addition to that, the behaviour of those devices in different aging environments such as in Standard Testing Conditions, Indoor illumination and under particle irradiation will be presented elucidating the role played by the architectures and materials in affecting the overall stability of the solar cells  [4-6].

[1] N.Ren et al. iEnergy, 2024, 10.23919/IEN.2024.0001

[2] Y. Hu, et al., ACS Energy Lett. 2021, doi.org/10.1021/acsenergylett.1c01193.

[3] J. Wu, et al., Sci. China Mater. 2022,doi.org/10.1007/s40843-022-2075-7

[4] F. Jafarzadeh et al., Sust. En. & Fuels, 2023, 7(9), 2219-2228. https://doi.org/10.1039/D2SE01678H

[5] D. Machado et a. Advanced Sustainable Systems, under review.

[6] S.Noola et al. Sustainable Energy and Fuels, under review

[7] F.De Rossi et al. Neutron irradiated perovskite films and solar cells on PET substrates, Nano Energy 93 (2022) 106879, https://doi.org/10.1016/j.nanoen.2021.106879

ISOS protocols provide a framework for comparing the stability of lab-scale solar cells. Comparability depends on documenting the stressing conditions (atmosphere, temperature, bias, light). However, the electrodes’ layout and quality can falsify the measurement.

Small-area samples are often based on substrates with pre-deposited transparent conducting electrodes (TCEs). It is popular that the TCE is shared with multiple solar cell devices deposited on the substrate. In this case, it becomes a common electrode. In some cases, the TCEs are not metalized.

A non-metalized common electrode presents two problems: a high contact resistance and the reciprocal influence of the devices sharing the common electrode.

The most common stability measurement entails MPP tracking of multiple devices in parallel for statistical validation.

We analyzed the deviation of the PV parameters caused by a common electrode with simulations and confirmed them with experimental measurements. We considered the JV of devices with increasing contact resistance and with a shunted neighboring device. The estimated MPP is comparable to the one obtained from continuous MPP tracking.

The contact resistance varied from 0.001 to 100Ω. A contact resistance of 1Ω is sufficient to introduce a significant error in the MPP estimation. If a neighboring pixel shunts, it increases the deviation and causes a Voc overestimation. Such deviations falsify any result obtained from stability tests and JV measurements.

For reliable parallel stability testing, a common electrode should be avoided. Metallization of the electrode is necessary to minimize the contact resistance. However, the choice of the metal matters, as it might react with other layers and be unstable to environmental stressors like humidity and oxygen. An extreme case is silver paste on ITO. We compared it with a copper electrode with an MPP tracking test with a humidity of about 8%. The device with a copper electrode had a lifetime which was four times longer. This indicates that the material and deposition process of the contact requires careful selection.

Bibliography
[1] M. Fischer, D. Kiermasch, L. Gil-Escrig, H. J. Bolink, V. Dyakonov, K. Tvingstedt, Sustainable Energy
Fuels 2021, 5, 3578.

Perovskite solar cells (PSC) have gained tremendous attention due to their excellent power conversion efficiency (PCE) and their potential for low-cost, scalable production. However, one of the critical challenges hindering their widespread commercialization is their stability under various environmental conditions, as humidity, light and heat.

In this study, we investigate the stability of flexible fully printed PSC devices via the standardized protocols established by the International Summit on Organic Photovoltaic Stability (ISOS), and the results are correlated with the analysis of Spectroscopic Ellipsometry (SE) and Laser Beam Induced Current (LBIC) measurements, to systematically explore and contribute to the understanding of the degradation mechanisms as well as to identify strategies towards the stability enhancement.

The flexible fully printed PSC devices were fabricated by the sequential printing of PEDOT:PSS/MAPbI3/PC60BM/AgNWs layers on top of flexible PET/IMI substrates, and their stability was studied under the ISOS-L1, ISOS-L2, ISOS-D2, and ISOS-D3 protocols. Our findings indicate that humidity has the most significant impact on the PSC degradation, causing a 60% drop in PCE within a few hours. Temperature also significantly affected the devices degradation, while the radiation caused less severe effects. Additionally, we evaluated the kinetics using Accelerated Lifetime Testing models at temperatures of 45°C and 65°C to gain deeper insights into the stability kinetics. Furthermore, the analysis of the in-situ and real-time SE spectra enabled monitoring of the time evolution of the MAPI, PbI2 and the voids volume fractions in MAPbI3 films exposed to humidity and light.

Flexible perovskite solar cells (f-PSCs) hold the promise to be game-changers for a wide range of applications (e.g. IoT, portable and wearable electronics, space), where flexibility, conformability, lightweight and high power-to-weight ratio are instrumental and sought-after. Beside their remarkable efficiency, as high as 25% , f-PSCs present additional appealing features: f-PSC fabrication is based on abundant materials and low-cost manufacture via solution processes; series- interconnected monolithic modules have been demonstrated on large area substrates, reaching up to 15.5% PCE on 100 cm2. Yet, as for their counterparts on rigid glass, f-PSC long-term stability is still an open issue, depending on several factors, both intrinsic and extrinsic. An effective encapsulation, able to ensure f-PSCs long-term stability providing protection from extrinsic agents, such as moisture, water, and oxygen, without compromising the overall flexibility of the device, is of extreme interest. Thermosetting polyurethanes (PUs) arise as promising candidates: they are inert toward the perovskite layer, and their curing reaction can easily be performed at room temperature, directly on the f-PSC.
Moreover, minimal modifications on the precursors&apos; skeleton can tune flexibility, barrier properties, and transparency. We present the successful implementation of a low-cost thermosetting PU resin as the encapsulant for 1 cm2 f-PSCs. Two encapsulation strategies are proposed: the PU is applied only on the back of the device (i.e., in contact with the metal electrode) or on both the back and the front, onto the PET substrate. Besides preserving the device flexibility, the double encapsulation strategy allows for very long stability under a highly damp atmosphere (RH > 75%), reaching T80 of over 550 hours (i.e., 23 days), clearly outperforming the unencapsulated control devices, whose T80 is 6 hours only.

This talk will present two studies on outdoor stability of monolithic perovskite / silicon tandem solar cells. The first one is about glass/glass encapsulated devices with an area of 9 cm² and compares two encapsulation schemes. The second one shows statistics on forty-five tandems integrated into photoelectrochemical cells producing solar hydrogen [1]. To do so, the devices have been interconnected  and the glass encapsulation has been adapted which made it possible to reach a total active area of 342 cm². Finally, the development of an imaging method will be presented. It is based on electroluminescence and localizes the ohmic shunt in the perovskite top-cell in 2T configuration.[2]

References

[1]. Maragno ARA, Cwicklinski G, Matheron M, Vanoorenberghe R, Borgard JM, Morozan A, et al. A scalable integrated solar device for the autonomous production of green methane. Joule. 2024 Aug;8(8):2325–41; Maragno ARA, Morozan A, Fize J, Pellat M, Artero V, Charton S, et al. Thermally integrated photoelectrochemical devices with perovskite/silicon tandem solar cells: a modular approach for scalable direct water splitting. Sustainable Energy Fuels. 2024 Aug 6;8(16):3726–39.

[2] Wyttenbach J. and Matheron M. Top-cell ohmic shunt imaging in 2-terminal tandem solar cells by differential electroluminescence, under review

The limited stability of perovskite solar cells remains a critical factor impeding their transition from laboratory settings to commercial production. Addressing this challenge requires not only improving the quality of perovskite active material but also ensuring its reliable performance in conjunction with other device layers. In this talk, I will discuss strategies to enhance the stability of perovskite solar cells by optimizing the interfaces between the active material and charge transport layers. I will first examine the role of bulky cations in passivating interfaces to achieve damp heat stable perovskite solar cells. Following this, I will emphasize the significance of energetic alignment between the perovskite layer and the hole transport layer and its impact on long-term photostability of perovskite solar cells. I will conclude my talk by introducing strategies for performing microscopic evaluation of the perovskite top interface using advanced imaging characterization.

All-inorganic cesium lead triiodide (CsPbI3) perovskites exhibit the advantages of excellent thermal and optical stability, various fabrication methods, and compatibility for constructing tandem devices with silicon or other narrow-bandgap perovskite solar cells. However, the CsPbI3 perovskites exhibit various phases, such as α, β, and γ phases, and the annealing temperature is as high as 350°C[1], which increases the energy cost of the manufacturing process. The high-temperature process limits their potential applications on flexible substrates. In addition, the CsPbI3 perovskites are easy to convert into the yellow phase (δ), leading to a large number of defects. Therefore, the development of low-temperature co-evaporated inorganic perovskite films has been initiated in recent years[2]; however, the random orientation and small grain size of low-temperature co-evaporated CsPbI3 thin films result in detrimental defects and non-radiative recombination. In this study, we introduced guanidinium iodide (GAI) into the co-evaporated CsPbI3 thin films to prepare γ-CsPbI3 all-inorganic perovskite solar cells with fewer defects, low-temperature phase transition, and highly preferential orientation. The p-i-n photovoltaic device based on this film achieves a power conversion efficiency of 15% with suppressed non-radiative recombination, comparable to the devices fabricated by the high-temperature (~350°C) process. This in-situ evaporation process alloying strategy paves the way for crystallization and defect control of the co-evaporated perovskite films.

Bibliography:

[1] HUANG, Qingrong, et al. Vapor-deposited CsPbI3 solar cells demonstrate an efficiency of 16. Science bulletin, 2021, 66.8: 757-760.

[2] DONG, Chong, et al. Co-evaporated oriented DMA1-xCsxPbI3 perovskite films for photovoltaics. Nano Energy, 2024, 120: 109159.

Further improvements in perovskite solar cells (PSCs) require better control of ionic defects in the perovskite photoactive layer during the manufacturing stage and their usage. Here, we report a living passivation strategy using a hindered urea/thiocarbamate bond Lewis acid-base material (HUBLA), where dynamic covalent bonds with water and heat-activated characteristics can dynamically heal the perovskite to ensure device performance and stability. Upon exposure to moisture or heat, HUBLA generates new agents and further passivates defects in the perovskite. This passivation strategy achieved high-performance devices with a power conversion efficiency (PCE) of 25.1%. HUBLA devices retained 94% of their initial PCE for approximately 1500 hours of aging at 85 °C in N2 and maintained 88% of their initial PCE after 1000 hours of aging at 85 °C and 30% relative humidity in air. (1)

Bibliography

(1) Wang, WT., Holzhey, P., Zhou, N., Zhang, Q. et al. Water- and heat-activated dynamic passivation for perovskite photovoltaics. Nature (2024). https://doi.org/10.1038/s41586-024-07705-5