Hazard potential of perovskite solar cell technology for potential implementation of "safe-by-design" approach

Achievements, challenges, and future prospects for industrialization of perovskite solar cells

In just over a decade, certified single-junction perovskite solar cells (PSCs) boast an impressive power conversion efficiency (PCE) of 26.1%. Such outstanding performance makes it highly viable for further development. Here, we have meticulously outlined challenges that arose during the industrialization of PSCs and proposed their corresponding solutions based on extensive research. We discussed the main challenges in this field including technological limitations, multi-scenario applications, sustainable development, etc. Mature photovoltaic solutions provide the perovskite community with invaluable insights for overcoming the challenges of industrialization. In the upcoming stages of PSCs advancement, it has become evident that addressing the challenges concerning long-term stability and sustainability is paramount. In this manner, we can facilitate a more effective integration of PSCs into our daily lives.

Toward the Commercialization of Perovskite Solar Modules

Perovskite (PVSK) photovoltaic (PV) devices are undergoing rapid development and have reached a certified power conversion efficiency (PCE) of 26.1% at the cell level. Tremendous efforts in material and device engineering have also increased moisture, heat, and light-related stability. Moreover, the solution-process nature makes the fabrication process of perovskite photovoltaic devices feasible and compatible with some mature high-volume manufacturing techniques. All these features render perovskite solar modules (PSMs) suitable for terawatt-scale energy production with a low levelized cost of electricity (LCOE). In this review, the current status of perovskite solar cells (PSCs) and modules and their potential applications are first introduced. Then critical challenges are identified in their commercialization and propose the corresponding solutions, including developing strategies to realize high-quality films over a large area to further improve power conversion efficiency and stability to meet the commercial demands. Finally, some potential development directions and issues requiring attention in the future, mainly focusing on further dealing with toxicity and recycling of the whole device, and the attainment of highly efficient perovskite-based tandem modules, which can reduce the environmental impact and accelerate the LCOE reduction are put forwarded.

Comprehensive Neurotoxicity of Lead Halide Perovskite Nanocrystals in Nematode Caenorhabditis elegans

To date, all-inorganic lead halide perovskite quantum dots have emerged as promising materials for photonic, optoelectronic devices, and biological applications, especially in solar cells, raising numerous concerns about their biosafety. Most of the studies related to the toxicity of perovskite quantum dots (PeQDs) have focused on the potential risks of hybrid perovskites by using zebrafish or human cells. So far, the neurotoxic effects and fundamental mechanisms of PeQDs remain unknown. Herein, a comprehensive methodology is designed to investigate the neurotoxicity of PeQDs by using Caenorhabditis elegans as a model organism. The results show that the accumulation of PeQDs mainly focuses on the alimentary system and head region. Acute exposure to PeQDs results in a decrease in locomotor behaviors and pharyngeal pumping, whereas chronic exposure to PeQDs causes brood decline and shortens lifespan. In addition, some abnormal issues occur in the uterus during reproduction assays, such as vulva protrusion, impaired eggs left in the vulva, and egg hatching inside the mother. Excessive reactive oxygen species formation is also observed. The neurotoxicity of PeQDs is explained by gene expression. This study provides a complete insight into the neurotoxicity of PeQD and encourages the development of novel nontoxic PeQDs.

Learning from Safe-by-Design for Safe-and-Sustainable-by-Design: Mapping the current landscape of Safe-by-Design reviews, case studies, and frameworks

With the introduction of the European Commission's "Safe and Sustainable-by-Design" (SSbD) framework, the interest in understanding the implications of safety and sustainability assessments of chemicals, materials, and processes at early-innovation stages has skyrocketed. Our study focuses on the "Safe-by-Design" (SbD) approach from the nanomaterials sector, which predates the SSbD framework. In this assessment, SbD studies have been compiled and categorized into reviews, case studies, and frameworks. Reviews of SbD tools have been further classified as quantitative, qualitative, or toolboxes and repositories. We assessed the SbD case studies and classified them into three categories: safe(r)-by-modeling, safe(r)-by-selection, or safe(r)-by-redesign. This classification enabled us to understand past SbD work and subsequently use it to define future SSbD work so as to avoid confusion and possibilities of "SSbD-washing" (similar to greenwashing). Finally, the preexisting SbD frameworks have been studied and contextualized against the SSbD framework. Several key recommendations for SSbD based on our analysis can be made. Knowledge gained from existing approaches such as SbD, green and sustainable chemistry, and benign-by-design approaches needs to be preserved and effectively transferred to SSbD. Better incorporation of chemical and material functionality into the SSbD framework is required. The concept of lifecycle thinking and the stage-gate innovation model need to be reconciled for SSbD. The development of high-throughput screening models is critical for the operationalization of SSbD. We conclude that the rapid pace of both SbD and SSbD development necessitates a regular mapping of the newly published literature that is relevant to this field.

Soil adsorption and transport of lead in the presence of perovskite solar cell-derived organic cations

Perovskite photovoltaics offer a highly efficient and low-cost solar energy harvesting technology. However, the presence of lead (Pb) cations in photovoltaic halide perovskite (HaPs) materials is concerning, and quantifying the environmental hazard of accidental Pb²⁺ leaching into the soil is crucial for assessing the sustainability of this technology. Pb²⁺ from inorganic salts was previously found to remain in the upper soil layers due to adsorption. However, Pb-HaPs contain additional organic and inorganic cations, and competitive cation adsorption may affect Pb²⁺ retention in soils. Therefore, we measured, analyzed by simulations and report the depths to which Pb²⁺ from HaPs penetrates into 3 types of agricultural soil. Most of the HaP-leached Pb²⁺ is found to be retained already in the first cm of the soil columns, and subsequent rain events do not induce Pb²⁺ penetration below the first few cm of soil surface. Surprisingly, organic co-cations from the dissolved HaP are found to enhance the Pb²⁺ adsorption capacity in clay-rich soil, compared to non-HaP-based Pb²⁺ sources. Our results imply that installation over soil types with improved Pb²⁺ adsorption, and removal of only the contaminated topsoil, are sufficient means to prevent ground water contamination by HaP-leached Pb²⁺.

Study on myocardial toxicity induced by lead halide perovskites nanoparticles

Lead halide perovskites (LHPs) are outstanding candidates for next-generation optoelectronic materials, with considerable prospects of use and commercial value. However, knowledge about their toxicity is scarce, which may limit their commercialization. Here, for the first time, we studied the cardiotoxicity and molecular mechanisms of representative CsPbBr3 nanoparticles in LHPs. After their intranasal administration to Institute of Cancer Research (ICR) mice, using advanced synchrotron radiation, mass spectrometry, and ultrasound imaging, we revealed that CsPbBr3 nanoparticles can severely affect cardiac systolic function by accumulating in the myocardial tissue. RNA sequencing and Western blotting demonstrated that CsPbBr3 nanoparticles induced excessive oxidative stress in cardiomyocytes, thereby provoking endoplasmic reticulum stress, disturbing calcium homeostasis, and ultimately leading to apoptosis. Our findings highlight the cardiotoxic effects of LHPs and provide crucial toxicological data for the product.

Lead immobilization for environmentally sustainable perovskite solar cells

Lead halide perovskites are promising semiconducting materials for solar energy harvesting. However, the presence of heavy-metal lead ions is problematic when considering potential harmful leakage into the environment from broken cells and also from a public acceptance point of view. Moreover, strict legislation on the use of lead around the world has driven innovation in the development of strategies for recycling end-of-life products by means of environmentally friendly and cost-effective routes. Lead immobilization is a strategy to transform water-soluble lead ions into insoluble, nonbioavailable and nontransportable forms over large pH and temperature ranges and to suppress lead leakage if the devices are damaged. An ideal methodology should ensure sufficient lead-chelating capability without substantially influencing the device performance, production cost and recycling. Here we analyse chemical approaches to immobilize Pb2+ from perovskite solar cells, such as grain isolation, lead complexation, structure integration and adsorption of leaked lead, based on their feasibility to suppress lead leakage to a minimal level. We highlight the need for a standard lead-leakage test and related mathematical model to be established for the reliable evaluation of the potential environmental risk of perovskite optoelectronics.

Fate and Exposure Assessment of Pb Leachate from Hypothetical Breakage Events of Perovskite Photovoltaic Modules

Emerging lead halide perovskite (LHP) photovoltaics are undergoing intense research and development due to their outstanding efficiency and potential for low manufacturing costs that render them competitive with existing photovoltaic (PV) technologies. While today's efforts are focused on stability and scalability of LHPs, the toxicity of lead (Pb) remains a major challenge to their large-scale commercialization. Here, we present a screening-level, EPA-compliant model of fate and transport of Pb leachate in groundwater, soil, and air, following hypothetical catastrophic breakage of LHP PV modules in conceptual utility-scale sites. We estimated exposure point concentrations of Pb in each medium and found that most of the Pb is sequestered in soil. Exposure point concentrations of Pb from the perovskite film fell well below EPA maximum permissible limits in groundwater and air even upon catastrophic release from PV modules at large scales. Background Pb levels in soil can influence soil regulatory compliance, but the highest observed concentrations of perovskite-derived Pb would not exceed EPA limits under our assumptions. Nonetheless, regulatory limits are not definitive thresholds of safety, and the potential for increased bioavailability of perovskite-derived Pb may warrant additional toxicity assessment to further characterize public health risks.

Highly effective biosorption capacity of Cladosporium sp. strain F1 to lead phosphate mineral and perovskite solar cell PbI2

Fungus Cladosporium sp. strain F1 showed highly effective biosorption capacity to lead phosphate mineral and perovskite solar cells lead iodide compared to other fungi Aspergillus niger VKMF-1119 and Mucor ramannianus R-56. Scanning electron microscopy and transmission electron microscopy analyses shows that Cladosporium sp. strain F1, which previously showed high biosorption capacity to uranium phosphate nanorods and nanoplates, can accumulate lead phosphate mineral and lead iodide on the fungal hyphae surface in large amounts under a wide range of pH conditions, while A. niger VKMF-1119 and M. ramannianus R-56 adsorbed small amounts of minerals. After biosorption of lead iodide minerals on Cladosporium sp. strain F1, aqueous dimethyl sulfoxide (50%) at pH 2 (70 °C) released the mineral more than 99%. Based on the fungal surface analyses, hydrophobic properties on the surfaces of Cladosporium sp. strain F1 could affect the higher biosorption capacity of strain F1 to lead phosphate mineral and lead iodide as compared to other tested fungi. Cladosporium sp. strain F1 may be the novel biosorbents to remediate the phosphate rich environment and to recover lead from perovskite solar cells lead iodide.

Lead-binding biogenic polyelectrolyte multilayer coating for lead retention in perovskite solar cells

Perovskite solar cells promise to deliver high efficiencies at low manufacturing costs. Yet on their way towards commercialization, they have to face the associated risk of potential lead leakage into the environment after damage to the cell's encapsulation. Here we present a new approach to generate a lead binding coating, based on a layer-by-layer deposition of biopolymers. A lead-adsorbing functionality was shown after subsequent crosslinking, demonstrating a high binding capacity. The lead binding capabilities could be further enhanced by increasing the thickness of the coatings, analyzed both in the supernatant and on the surface of the coated material. The thin-layered coating had a thickness of less than one micrometer, was stable even under low pH conditions and could successfully be transferred onto different substrates, ranging from silicon, gold and glass substrates to polymeric nonwoven materials with high surface areas, further increasing its lead binding capacity. This newly described coating was applied within perovskite solar cell stacks without impeding the overall efficiency but strongly reducing the amount of lead released after simulated rain tests on devices with damaged encapsulation. Accordingly, incorporation of lead-binding polyelectrolyte multilayers inside the encapsulation of perovskite solar cells shows great potential to limit the perovskite solar cells inherent risk of lead leakage in a sustainable manner.

Pyridine Controlled Tin Perovskite Crystallization

Controlling the crystallization of perovskite in a thin film is essential in making solar cells. Processing tin-based perovskite films from solution is challenging because of the uncontrollable faster crystallization of tin than the most used lead perovskite. The best performing devices are prepared by depositing perovskite from dimethyl sulfoxide because it slows down the assembly of the tin-iodine network that forms perovskite. However, while dimethyl sulfoxide seems the best solution to control the crystallization, it oxidizes tin during processing. This work demonstrates that 4-(tert-butyl) pyridine can replace dimethyl sulfoxide to control the crystallization without oxidizing tin. We show that tin perovskite films deposited from pyridine have a 1 order of magnitude lower defect density, which promotes charge mobility and photovoltaic performance.

Potential lead toxicity and leakage issues on lead halide perovskite photovoltaics

Recently, lead halide perovskite solar cells have become a promising next-generation photovoltaics candidate for large-scale application to realize low-cost renewable electricity generation. Although perovskite solar cells have tremendous advantages such as high photovoltaic performance, low cost and facile solution-based fabrication, the issues involving lead could be one of the main obstacles for its commercialization and large-scale applications. Lead has been widely used in photovoltaics industry, yielding its environmental and health issues of vital importance because of the widespread application of photovoltaics. When the solar cell panels especially perovskite solar cells are damaged, lead would possibly leak into the surrounding environment, causing air, soil and groundwater contamination. Therefore, lots of research efforts have been put into evaluating the lead toxicity and potential leakage issues, as well as studying the encapsulation of lead to deal with leakage issue during fire hazard and precipitation in photovoltaics. In this review, we summarize the latest progress on investigating the lead safety issue on photovoltaics, especially lead halide perovskite solar cells, and the corresponding solutions. We also outlook the future development towards solving the lead safety issues from different aspects.

Encapsulation Strategies for Highly Stable Perovskite Solar Cells under Severe Stress Testing: Damp Heat, Freezing, and Outdoor Illumination Conditions

A key direction toward managing extrinsic instabilities in perovskite solar cells (PSCs) is encapsulation. Thus, a suitable sealing layer is required for an efficient device encapsulation, preventing moisture and oxygen ingression into the perovskite layer. In this work, a solution-based, low-cost, and commercially available bilayer structure of poly(methyl methacrylate)/styrene-butadiene (PMMA/SB) is investigated for PSCs encapsulation. Encapsulated devices retained 80% of the initial power conversion efficiency (PCE) at 85 °C temperature and 85% relative humidity after 100 h, while reference devices without SB (only PMMA) suffer from rapid and intense degradation after only 2 h, under the same condition. In addition, encapsulated devices retained 95% of the initial PCE under -15 °C freezing temperature after 6 h and retained ∼80% of the initial PCE after immersion in HCl (37%) for 90 min. Moreover, applying an additional aluminum metal sheet on the PMMA/SB protective bilayer leads to the improvement of device stability up to 500 h under outdoor illumination, retaining almost 90% of the initial PCE. Considering the urge to develop reliable, scalable, and simple encapsulation for future large-area PSCs, this work establishes solution-based bilayer encapsulation, which is applicable for flexible solar modules as well as other optoelectronic devices such as light-emitting devices and photodetectors.improvement of device stability up to 500 h under outdoor illumination, retaining almost 90% of the initial PCE. Considering the urge to develop reliable, scalable, and simple encapsulation for future large-area PSCs, this work establishes solution-based bilayer encapsulation, which is applicable for flexible solar modules as well as other optoelectronic devices such as light-emitting devices and photodetectors.

Comparative toxicity of potential leachates from perovskite and silicon solar cells in aquatic ecosystems

Globally, perovskite solar cells (PSCs) represent a third-generation photovoltaic technology that is being increasingly implemented and commercialized. However, the biological impacts of leachates from PSCs are poorly understood. Therefore, the aim of this study was to investigate the ecotoxicity of PSC leachates compared with that of commercial Si-based solar cell (SBSC) leachates. We performed leaching assessments and aquatic bioassays using internationally recommended test species and measured and compared the ecotoxicity of PSC and SBSC leachates. As a result of the leaching analyses, Si, Pb, and Al were found to be the most leached elements from broken PSCs and SBSCs. The bioassays indicated that polycrystalline SBSC (p-Si) and monocrystalline SBSC (m-Si) leachates were more toxic to fish embryos than the PSC leachates and that water fleas were sensitive to m-Si leachates, but less sensitive to PSC and p-Si leachates. In addition, principle component analyses indicated that the ecotoxicity of solar cell leachates was related to either the Pb or Si content. This is the first comparative study of the potential ecotoxicity of PSC and SBSC leachates in aquatic ecosystems, and the results of which can be used in the environmentally safe commercialization of solar cells.

Sublethal toxicity of PbI2 in perovskite solar cells to fish embryos (Danio rerio and Oryzias latipes): Deformity and growth inhibition

Pb-based perovskite in solar cells is a source of PbI₂. The objective of this study was to characterize the embryonic toxicity of PbI₂, a potentially leachable chemical and hazardous material, for two fish species (zebrafish and Japanese medaka). A series of measurements were performed to assess mortality, abnormalities (deformities and other pathological changes), hatchability, and growth inhibition. The results obtained showed that the toxicities observed were predominantly associated with Pb²⁺ and I^-. Therefore, given the potential ecotoxicity of PbI₂, precautions should be taken to prevent its release during the breakage and disposal of Pb-based perovskite solar cells.

An across-species comparison of the sensitivity of different organisms to Pb-based perovskites used in solar cells

Organic-inorganic perovskite solar cells (PSCs) are promising candidates as photovoltaic cells. Recently, they have attracted significant attention due to certified power conversion efficiencies exceeding 23%, low-cost engineering, and superior electrical/optical characteristics. These PSCs extensively utilize a perovskite-structured composite with a hybrid of Pb-based nanomaterials. Operation of them may cause the release of Pb-based nanoparticles. However, limited information is available regarding the potential toxicity of Pb-based PSCs on various organisms. This study conducted a battery of in vitro and in vivo toxicity bioassays for three quintessential Pb-based PSCs (CH₃NH₃PbI₃, NHCHNH₃PbBr₃, and CH₃NH₃PbBr₃) using progressively more complex forms of life. For all species tested, the three different perovskites had comparable toxicities. The viability of Caco-2/TC7 cells was lower than that of A549 cells in response to Pb-based PSC exposure. Concentration-dependent toxicity was observed for the bioluminescent bacterium Vibrio fischeri, for soil bacterial communities, and for the nematode Caenorhabditis elegans. Neither of the tested Pb-based PSCs particles had apparent toxicity to Pseudomonas putida. Among all tested organisms, V. fischeri showed the highest sensitivity with EC₅₀ values (30 min of exposure) ranging from 1.45 to 2.91 mg L^-1. Therefore, this study recommends that V. fischeri should be preferably utilized to assess. PSC toxicity due to its increased sensitivity, low costs, and relatively high throughput in a 96-well format, compared with the other tested organisms. These results highlight that the developed assay can easily predict the toxic potency of PSCs. Consequently, this approach has the potential to promote the implementation of the 3Rs (Replacement, Reduction, and Refinement) principle in toxicology and decrease the dependence on animal testing when determining the safety of novel PSCs.

On-device lead sequestration for perovskite solar cells

Perovskite solar cells, as an emerging high-efficiency and low-cost photovoltaic technology^1-6, face obstacles on their way towards commercialization. Substantial improvements have been made to device stability^7-10, but potential issues with lead toxicity and leaching from devices remain relatively unexplored^11-16. The potential for lead leakage could be perceived as an environmental and public health risk when using perovskite solar cells in building-integrated photovoltaics^17-23. Here we present a chemical approach for on-device sequestration of more than 96 per cent of lead leakage caused by severe device damage. A coating of lead-absorbing material is applied to the front and back sides of the device stack. On the glass side of the front transparent conducting electrode, we use a transparent lead-absorbing molecular film containing phosphonic acid groups that bind strongly to lead. On the back (metal) electrode side, we place a polymer film blended with lead-chelating agents between the metal electrode and a standard photovoltaic packing film. The lead-absorbing films on both sides swell to absorb the lead, rather than dissolve, when subjected to water soaking, thus retaining structural integrity for easy collection of lead after damage.