Potential lead toxicity and leakage issues on lead halide perovskite photovoltaics

Comparative life cycle assessment of integrated renewable energy-based power systems

Integrated renewable-based power cycles should be employed to produce more sustainable electricity. This is a comparative life cycle assessment (LCA) of three combined power plants, encompassing: case 1 involving combined geothermal and wind, case 2 featuring combined geothermal and solar, and case 3 integrating wind and solar systems. The base case perovskite solar cell (PSC) modelling assumes a 3-year lifespan and a power conversion efficiency of 17 %. However, diverse scenarios are evaluated through a sensitivity assessment involving enhancements in lifetime and efficiency. The base case evaluation emphasizes that the phases with the most significant negative environmental effects which includes the drilling of geothermal wells, construction of wind plants, and manufacturing and installation of PSCs. The midpoint findings indicate that boosting the power conversion efficiency of PSC from 17 % to 35 % yields a notable decrease in environmental impact. Moreover, extending the lifetime from 3 to 15 years led to reduction in CO2 emissions from 0.0373 and 0.0185 kg CO2 eq/kWh to 0.026 and 0.0079 kg CO2 eq/kWh in cases 2 and 3, respectively. Assessing worst and best-case scenarios highlights significant declines in certain impact categories. In case 3, terrestrial ecotoxicity (TE), photochemical oxidant formation (POF), human toxicity (HT), marine ecotoxicity (ME), and marine eutrophication (MU) saw reductions exceeding 88 % compared to worst-case results. The environmental effects observed in cases 2 and 3 stem from toxicity and metal depletion, mainly linked to the PSC. Endpoint results revealed that when considering a PSC lifespan of 10 years or more, the detrimental ecosystem impacts of cases 2 and 3 become less severe than those of case 1. Uncertainty assessment has been done for different cases and impact categories. The study's results are also novel in which it evaluated the innovative PSC technology when integrated with other renewable resources, contrasting it with other integrated plants.

Plasma-Based Modification of Tin Halide Perovskite Interfaces for Photovoltaic Applications

Tin halide perovskites represent the most suitable alternative to their lead-based counterparts for sustainable photovoltaics. One of the most important drawbacks of this class of materials is the intrinsic tendency of tin (II) to oxidize under certain conditions and as a consequence of aging. Here, we explore plasma processing to gently treat the surface of the tin perovskite films. As shown by chemical, optical, and morphological analyses, this treatment by generating transient active species on the surface of the material impacts its aging, inhibiting the tendency of tin (II) to oxidize. Plasma-treated stored devices show a power conversion efficiency slightly higher and narrower in the distribution than that of the reference devices. The positive impact of this noninvasive technique, which can be easily implemented in large-area manufacturing facilities, increases the potential of lead-free alternative perovskite photovoltaics.

Single Layer of Crown Ether Enables Efficient, Stable, and Pb Leakage-Free Inverted Perovskite Solar Cells

Significant challenges in ensuring long-term stability, addressing environmental safety issues, and improving efficiency have hindered the commercialization of inverted Pb-based halide perovskite solar cells (PeSCs). One reasonable approach to addressing these issues is to place an effective buffer layer between the perovskite active layer and the electrode. In this study, we demonstrate the use of crown ether, di-tert-butyl dibenzo-18-crown-6, as a single buffer layer to improve the efficiency, long-term stability, and environmental safety of PeSCs for the first time. The crown ether buffer layer suppressed Ag diffusion from the Ag metal electrodes, thereby improving the performance and lifetime of the device. In addition, it effectively captures Pb ions that may leak into the environment during the whole lifetime of devices, thereby enhancing the environmental safety of PeSCs. Furthermore, PeSCs incorporating crown ethers as buffer layers demonstrated enhanced stability in a nitrogen atmosphere and achieved a high power conversion efficiency of 22.8%. Consequently, this crown ether buffer layer offers an effective and straightforward strategy capable of achieving efficient, stable, and environmentally safe PeSCs.

Impact of Bi2O3 on prepared nano (SiO2-Na2O-CaO-B2O3) glass as radiation shielding material

Melt quenching technique was used to create Bismuth Boro-Silicate nano glasses with compositions of 45SiO2-10CaO- 25Na2O- xBi2O3- (20-x) B2O3 (where x is 0, 5, 10, 15, and 20 mol %). Standard point sources AM-241, Ba-133, Co-60, Cs-137, and Eu-152 were used in the radiation experiment to evaluate the attenuation coefficients spanning the energy range of 59.51 keV to 1048.01 keV. The findings show that adding Bi2O3 in place of B2O3 increases the following: radiation protection efficiency (RPE%), transmission factor (TF%), absorption buildup factor values (ABF), exposure buildup factor values (EBF), mass attenuation coefficients (MACs), linear attenuation coefficients (LACs), and radiation protection efficiency (RPE%). In comparison to lead glass, these findings demonstrate the potential of nano Bismuth Boro-Silicate glass as a radiation shielding material.

Lead Isolation and Capture in Perovskite Photovoltaics toward Eco-Friendly Commercialization

Perovskite solar cells (PSCs) are developed rapidly in efficiency and stability in recent years, which can compete with silicon solar cells. However, an important obstacle to the commercialization of PSCs is the toxicity of lead ions (Pb2+) from water-soluble perovskites. The entry of free Pb2+ into organisms can cause severe harm to humans, such as blood lead poisoning, organ failure, etc. Therefore, this work reports a "lead isolation-capture" dual detoxification strategy with calcium disodium edetate (EDTA Na-Ca), which can inhibit lead leakage from PSCs under extreme conditions. More importantly, leaked lead exists in a nontoxic aggregation state chelated by EDTA. For the first time, in vivo experiments are conducted in mice to systematically prove that this material has a significant inhibitory effect on the toxicity of perovskites. In addition, this strategy can further enhance device performance, enabling the optimized devices to achieve an impressive power conversion efficiency (PCE) of 25.19%. This innovative strategy is a major breakthrough in the research on the prevention of lead toxicity in PSCs.

Stable and Lead-Safe Polyphenol-Encapsulated Perovskite Solar Cells

Lead (Pb) halide perovskite solar cells (PSCs) exhibit impressive power conversion efficiencies close to those of their silicon counterparts. However, they suffer from moisture instability and Pb safety concerns. Previous studies have endeavoured to address these issues independently, yielding minimal advancements. Here, a general nanoencapsulation platform using natural polyphenols is reported for Pb-halide PSCs that simultaneously addresses both challenges. The polyphenol-based encapsulant is solution-processable, inexpensive (≈1.6 USD m-2), and requires only 5 min for the entire process, highlighting its potential scalability. The encapsulated devices with a power conversion efficiency of 20.7% retained up to 80% of their peak performance for 2000 h and up to 70% for 7000 h. Under simulated rainfall conditions, the encapsulant rich in catechol groups captures the Pb ions released from the degraded perovskites via coordination, keeping the Pb levels within the safe drinking water threshold of 15 ppb.

Counter-Doping Effect by Trivalent Cations in Tin-Based Perovskite Solar Cells

Tin (Sn) -based perovskite solar cells (PSCs) normally show low open circuit voltage due to serious carrier recombination in the devices, which can be attributed to the oxidation and the resultant high p-type doping of the perovskite active layers. Considering the grand challenge to completely prohibit the oxidation of Sn-based perovskites, a feasible way to improve the device performance is to counter-dope the oxidized Sn-based perovskites by replacing Sn2+ with trivalent cations in the crystal lattice, which however is rarely reported. Here, the introduction of Sb3+, which can effectively counter-dope the oxidized perovskite layer and improve the carrier lifetime, is presented. Meanwhile, Sb3+ can passivate deep-level defects and improve carrier mobility of the perovskite layer, which are all favorable for the photovoltaic performance of the devices. Consequently, the target devices yield a relative enhancement of the power conversion efficiency (PCE) of 31.4% as well as excellent shelf-storage stability. This work provides a novel strategy to improve the performance of Sn-based PSCs, which can be developed as a universal way to compensate for the oxidation of Sn-based perovskites in optoelectronic devices.

Room temperature synthesis of nanocomposite thin films with embedded Cs2AgIn0.9Bi0.1Cl6 lead-free double perovskite nanocrystals with long-term water stability, wide range pH tolerance, and high quantum yield

The synthesis of Cs2AgIn0.9Bi0.1Cl6 nanocrystals was achieved at room temperature under ambient conditions using the ligand-assisted reprecipitation (LARP) method. The synthesized NCs exhibit bright orange emission when excited at 375 nm and have broad photoluminescence (PL) emission spectra with a maximum of 630 nm. A photoluminescence quantum yield (PLQY) of 36% was observed in these NCs without any polymer coatings. Polystyrene (PS), and poly (methyl methacrylate) (PMMA) were used to enhance the water stability and PLQY values up to 64%. Nanocomposite thin films with these polymer encapsulations exhibit good thermal stability up to at least 353 K and high quantum yields. PMMA-coated NCs showed long-term water stability for at least 4 months. The composites remain photostable when in contact with water for at least 120 min under continuous 365 nm UV illumination at 1 mW cm-2. Due to their excellent optical properties, aqueous stability, and wide range pH tolerance, these nanocomposite thin films could be employed for a variety of biological applications.

Exploiting halide perovskites for heavy metal ion detection

Heavy metal ions such as mercury (Hg), copper (Cu), and cadmium (Cd) pose significant threats to ecosystems and human health due to their toxicity and bioaccumulation potential. With growing environmental concerns over heavy metal ion pollution, there is an urgent need to develop efficient detection methods for safeguarding public health and the environment. Various materials, including polymers, nanomaterials, and porous substances, have been used for heavy metal ion detection and have shown promising performance for different scenarios. However, each of these materials has certain limitations as probes. Metal halide perovskites (MHPs), known for their exceptional optoelectronic properties and high structural and chemical tunability, have gained great attention in applications such as photovoltaics and LEDs. Yet, their potential as metal ion probes remains rarely explored. This review assesses MHPs as prospective materials for heavy metal ion detection, taking their structure, chemical properties, and responses to external stimuli into consideration. Three key detection mechanisms-cation exchange (CE), electron transfer (ET), and fluorescence resonance energy transfer (FRET), are explored to understand how metal ions trigger fluorescence changes on perovskites, enabling their detection. Finally, current avenues of developing perovskite probes are discussed, which include exploration of lead-free perovskites to mitigate environmental concerns arising from lead leakage and the pursuit of achieving high-sensitivity and stable detection in aqueous media, summarizing the existing and promising strategies in this field.

Crystallization Regulation and Lead Leakage Prevention Simultaneously for High-Performance CsPbI2Br Perovskite Solar Cells

All-inorganic CsPbI2Br perovskite is striking as a result of the reasonable band gap and thermal stability. However, the notorious air instability, unsatisfactory conversion efficiencies, and toxic water-soluble Pb2+ ions have greatly limited the further development of CsPbI2Br-based devices. Herein, a facile strategy is developed to prepare efficient and air-stable CsPbI2Br-based perovskite solar cells (PSCs) with in situ lead leakage protection. With the introduction of 2,2'-dihydroxy-4,4'-dimethoxy-5,5'-disulfobenzophenone disodium salt (BP-9) into the CsPbI2Br precursor solution, the crystallization of perovskite can be regulated at a reduced trap density, the uncoordinated Pb2+ ions and electron-rich defects in the structure can be passivated to suppress non-radiative recombination, and the energy level arrangement can be optimized to improve charge carrier transport. Consequently, the optimized PSC achieved a championship efficiency of 17.11%, accompanied by negligible J-V hysteresis and remarkably improved air stability. More importantly, the strong chelation of BP-9 with water-soluble Pb2+ ions minimizes the leakage of toxic lead in the perovskite structure.

Current State and Future Perspectives of Printable Organic and Perovskite Solar Cells

Photovoltaic technology presents a sustainable solution to address the escalating global energy consumption and a reliable strategy for achieving net-zero carbon emissions by 2050. Emerging photovoltaic technologies, especially the printable organic and perovskite solar cells, have attracted extensive attention due to their rapidly transcending power conversion efficiencies and facile processability, providing great potential to revolutionize the global photovoltaic market. To accelerate these technologies to translate from the laboratory scale to the industrial level, it is critical to develop well-defined and scalable protocols to deposit high-quality thin films of photoactive and charge-transporting materials. Herein, the current state of printable organic and perovskite solar cells is summarized and the view regarding the challenges and prospects toward their commercialization is shared. Different printing techniques are first introduced to provide a correlation between material properties and printing mechanisms, and the optimization of ink formulation and film-formation during large-area deposition of different functional layers in devices are then discussed. Engineering perspectives are also discussed to analyze the criteria for module design. Finally, perspectives are provided regarding the future development of these solar cells toward practical commercialization. It is believed that this perspective will provide insight into the development of printable solar cells and other electronic devices.

Synthesis of different organic ammonium-based bismuth iodide perovskites for photodetection application

Bismuth-based perovskites are promising candidates for highly stable halide perovskites with low toxicity. Here, we report the synthesis of a series of bismuth iodide-based perovskites with different primary, secondary, and tertiary ammonium cations and study their structural, thermal, and optical properties, and the likelihood of photodetection. Interestingly, the variation of A-site organic ammonium cations, with different interlayer spacings between adjacent bismuth iodide monolayers, has exotic effects on the diffraction patterns and morphological structures of the perovskite crystals. Thermogravimetric analysis reveals the highest thermal stability of tertiary ammonium-based bismuth perovskite with a decomposition temperature of 385 °C. The branched primary ammonium-based photodetector has photo-responsivity roughly two and four times faster than that of secondary and tertiary ammonium-based devices, respectively. These findings provide insight into the importance of A-site cation engineering for structural modulation and tailoring the optoelectronic properties of bismuth-based perovskites for emerging optoelectronic devices.

A review of toxicity assessment procedures of solar photovoltaic modules

Environmental management of solar photovoltaic (PV) modules is attracting attention as a growing number of field-operated PV modules approach end of life (EoL). PV modules may contain small amounts of toxic metals, and the procedures for assessing and regulating the toxic metal content and release of such materials at EoL differ widely across nations. This paper provides an overview of the metal composition of PV modules and common procedures for toxicity assessment through extensive research and review of technical literature and legislative documents. This review focuses on three primary aspects: first, it explores the distribution of toxic elements within current and emerging PV module designs, with a specific focus on obtaining representative samples for proportional toxicity testing within different module laminate areas. Second, it examines a sampling standard and the diverse toxicity testing methods and regulations employed in various regions, encompassing standards like the Environmental Protection Agency (EPA) Test Method 1311 (Toxicity Characteristic Leaching Procedure, TCLP) in the U.S., Restriction of Hazardous Substances (RoHS) in Europe, and the Waste Extraction Test (WET) in California. Third, the review examines the sources of variability in toxicity testing outcomes, including techniques for securing homogeneous samples from non-uniform PV modules, selecting particle sizes representative of landfill conditions in extracted samples, determining appropriate leachate characteristics such as leaching agents and pH levels, and considering factors like test duration and temperatures. In summary, this review summarizes relevant regulations and offers a comprehensive overview of the strengths and limitations associated with several toxicity assessment procedures currently in practice.

High-Stable Lead-Free Solar Cells Achieved by Surface Reconstruction of Quasi-2D Tin-Based Perovskites

Tin halide perovskites are an appealing alternative to lead perovskites. However, owing to the lower redox potential of Sn(II)/Sn(IV), particularly under the presence of oxygen and water, the accumulation of Sn(IV) at the surface layer will negatively impact the device's performance and stability. To this end, this work has introduced a novel multifunctional molecule, 1,4-phenyldimethylammonium dibromide diamine (phDMADBr), to form a protective layer on the surface of Sn-based perovskite films. Strong interactions between phDMADBr and the perovskite surface improve electron transfer, passivating uncoordinated Sn(II), and fortify against water and oxygen. In situ grazing incidence wide-angle X-ray scattering (GIWAXS) analysis confirms the enhanced thermal stability of the quasi-2D phase, and hence the overall enhanced stability of the perovskite. Long-term stability in devices is achieved, retaining over 90% of the original efficiency for more than 200 hours in a 10% RH moisture N2 environment. These findings propose a new approach to enhance the operational stability of Sn-based perovskite devices, offering a strategy in advancing lead-free optoelectronic applications.

Enhancing Performance and Stability of Sn-Pb Perovskite Solar Cells with Oriented Phenyl-C61-Butyric Acid Methyl Ester Layer via High-Temperature Annealing

Phenyl-C61-butyric acid methyl ester (PCBM) can be used as a passivation material in perovskite solar cells (PeSCs) in order to reduce the trap site of the perovskite. Here, we show that a thick PCBM layer can form a smoother surface on the SnO2 substrate, improving the grain size and reducing the microstrain of the perovskite. High-temperature annealing treatment of PCBM layer not only increases its solvent resistance to perovskite precursor or antisolvent, but also enhances its molecular alignment, resulting in improved conductivity as an electron transport layer. High-temperature annealed PCBM (HT-PCBM) effectively minimizes trap-assisted nonradiative recombination by reducing trap density in perovskite and improving the electrical properties at the interface between SnO2 and perovskite layers. This HT-PCBM process significantly enhances the performance of the PeSCs, including the open-circuit voltage (VOC) from 0.39 to 0.77 V, fill factor from 52% to 65%, and power conversion efficiency (PCE) from 6.03% to 15.50%, representing substantial improvements compared to devices without PCBM. This PCE is the highest efficiency among conventional (n-i-p) Sn-Pb PeSCs reported to date. Moreover, passivating the trap sites of SnO2 and separating the interface between the Sn-containing perovskite and the substrate effectively have improved the stability of the Sn-Pb perovskite in the n-i-p structure. The optimized best device with HT-PCBM has maintained an efficiency of over 90% for more than 300 h at 85 °C and 5000 h at room temperature in a glovebox atmosphere.

A zero-dimensional hybrid copper(I) bromide single crystal with highly efficient green emission

Lead-free metal halides are considered as alternatives to lead-based perovskites due to their low toxicity, rich structural diversity, and high luminescence properties. We report millimeter-sized single crystals of a new zero-dimensional (0D) copper(I)-based hybrid material, (AEP)2Cu2Br6·2Br·2H2O (AEP = C6H18N33+), which exhibits bright broadband green photoluminescence (PL) at 510 nm with a Stokes shift of 220 nm and a PL lifetime of 121.1 μs. Density functional theory (DFT) calculations and experimental studies reveal that the green light can be attributed to self-trapping exciton (STE) emission. It is worth mentioning that this crystal has a high photoluminescence quantum yield (PLQY) of 90.5%, which is higher than most copper halides.

Exploration of the origin of the excellent charge-carrier dynamics in Ruddlesden-Popper oxysulfide perovskite Y2Ti2O5S2

Although the efficient separation of electron-hole (e-h) pairs is one of the most sought-after electronic characteristics of materials, due to thermally induced atomic motion and other factors, they do not remain separated during the carrier transport process, potentially leading to rapid carrier recombination. Here, we utilized real-time time-dependent density functional theory in combination with nonadiabatic molecular dynamics (NAMD) to explore the separated dynamic transport path within Ruddlesden-Popper oxysulfide perovskite Y2Ti2O5S2 caused by the dielectric layer and phonon frequency difference. The underlying origin of the efficient overall water splitting in Y2Ti2O5S2 is systematically explored. We report the existence of the bi-directional e-h separate-path transport, in which, the electrons transport in the Ti2O5 layer and the holes diffuse in the rock-salt layer. This is in contrast to the conventional e-h separated distribution with a crowded transport channel, as observed in SrTiO3 and hybrid perovskites. Such a unique feature finally results in a long carrier lifetime of 321 ns, larger than that in the SrTiO3 perovskite (160 ns) with only one carrier transport channel. This work provides insights into the carrier transport in lead-free perovskites and yields a novel design strategy for next-generation functionalized optoelectronic devices.

Crystal Growth, Structural and Electronic Characterizations of Zero-Dimensional Metal Halide (TEP)InBr4 Single Crystals for X-Ray Detection

Recently, metal halides have shown great potential for applications such as solar energy harvesting, light emission, and ionizing radiation detection. In this work, we report the preparation, structural, thermal, and electronic properties of a new zero-dimensional (0D) halide (TEP)InBr4 (where TEP is tetraethylphosphonium organic cation, C8H20P+). (TEP)InBr4 single crystals are obtained within a few days of continuous crystal growth time via a solution growth methodology. (TEP)InBr4 shows a relatively large optical bandgap energy of 4.32 eV and a low thermal conductivity between 0.33±0.05 and 0.45±0.07 W/m-K. Based on the density functional theory (DFT) calculations, the highest occupied molecular orbitals (HOMOs) of (TEP)InBr4 are dominated by the Br states, while the lowest unoccupied molecular orbitals (LUMOs) are constituted by both In and Br states. (TEP)InBr4 single crystals exhibit a semiconductor resistivity of 1.73×1013 Ω·cm and a mobility-lifetime (mu-tau) product of 2.07×10-5 cm2/V. Finally, a prototype (TEP)InBr4 single crystal-based X-ray detector with a detection sensitivity of 569.85 uCGy-1cm-2 (at electrical field E=100 V/mm) was fabricated, indicating the potential use of (TEP)InBr4 for radiation detection applications.

Large-Area, Flexible, Lead-Free Sn-Perovskite Solar Modules

For the first time, large-area, flexible organic-inorganic tin perovskite solar modules are fabricated by means of an industry-compatible and scalable blade-coating technique. An 8-cell interconnected mini module with dimensions of 25 cm2 (active area = 8 × 1.5 cm2) reached 5.7% power conversion efficiency under 1000 W/m2 (AM 1.5G) and 9.4% under 2000 lx (white-LED).

Heavy metals distribution characteristics, source analysis, and risk evaluation of soils around mines, quarries, and other special areas in a region of northwestern Yunnan, China

In this study, based on the assessment of soil heavy metals (HMs) pollution using relevant indices, a comprehensive approach combined network environ analysis (NEA), human health risk assessment (HHRA) method and positive definite matrix factor (PMF) model to quantify the risks among ecological communities in a special environment around mining area in northwest Yunnan, calculated the risk to human health caused by HMs in soil, and analyzed the pollution sources of HMs. The integrated risks for soil microorganisms, vegetations, herbivores, and carnivores were 2.336, 0.876, 0.114, and 0.082, respectively, indicating that soil microorganisms were the largest risk receptors. The total hazard indexes (HI_T) for males, females, and children were 0.542, 0.591, and 1.970, respectively, revealing a relatively high and non-negligible non-carcinogenic risks (NCR) for children. The total cancer risks (TCR) for both females and children exceeded 1.00E-04, indicating that soil HMs posed carcinogenic risks (CR) to them. Comparatively, Pb was the high-risk metal, accounting for 53.76%, 57.90%, and 68.09% of HI_T in males, females, and children, respectively. PMF analysis yielded five sources of pollution, F1 (industry), F2 (agriculture), F3 (domesticity), F4 (nature), and F5 (traffic).

Leveraging machine learning to consolidate the diversity in experimental results of perovskite solar cells

Perovskite solar cells offer great potential for smart energy applications due to their flexibility and solution processability. However, the use of solution-based techniques has resulted in significant variations in device fabrication, leading to inconsistent results on the same composition. Machine learning (ML) and data science offer a potential solution to these challenges by enabling the automated design of perovskite solar cells. In this study, we leveraged machine learning tools to predict the band gap of hybrid organic-inorganic perovskites (HOIPs) and the power conversion efficiency of their solar cell devices. By analyzing 42 000 experimental datasets, we developed ML models for perovskite device design through a two-step predicting method, enabling the automation of perovskite materials development and device optimization. Additionally, band gap dependence of device parameters from experimental data is also validated, as predicted by the Shockley-Queisser model. This work has the potential to streamline the development of perovskite solar cells (PSCs) and optimize their performance without relying on time-consuming trial-and-error approaches.

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⁺.

Boosting efficiency of eco-friendly perovskite solar cell through optimization of novel charge transport layers

Formamidinium tin triiodide (FASnI3) is a suitable candidate for the absorber layer in perovskite solar cells (PSC) because of its non-toxicity, narrow band gap, thermal stability and high carrier mobility. This study focuses on the analysis and improvement in the performance of FASnI3-based PSCs using various inorganic charge transport materials. The copper-based materials such as Cu2O, CuAlO2, CuSCN and CuSbS2 are introduced as hole transport layers due to their earth abundance, ease of manufacturing, high charge mobilities and chemical stability. Similarly, fullerene derivates (PCBM and C60) are deployed as electron transport layers due to their mechanical strength, thermal conductivity and stability. The effect of these materials on optical absorption, quantum efficiency, energy band alignment, band offsets, electric field and recombination are studied in detail. The reasons for the low performance of the cell are identified and improved through design optimization. The PSC performance is analysed in both inverted and conventional architecture. Among all the structures, the best result is achieved through ITO/CuSCN/FASnI3/C60/Al with an efficiency of 27.26%, Voc of 1.08 V, Jsc of 29.5 mAcm-2 and FF of 85.6%.

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.

Synthesis of Thermally Stable and Highly Luminescent Cs5 Cu3 Cl6 I2 Nanocrystals with Nonlinear Optical Response

Low-dimensional Cu(I)-based metal halide materials are gaining attention due to their low toxicity, high stability and unique luminescence mechanism, which is mediated by self-trapped excitons (STEs). Among them, Cs₅ Cu₃ Cl₆ I₂ , which emits blue light, is a promising candidate for applications as a next-generation blue-emitting material. In this article, an optimized colloidal process to synthesize uniform Cs₅ Cu₃ Cl₆ I₂ nanocrystals (NCs) with a superior quantum yield (QY) is proposed. In addition, precise control of the synthesis parameters, enabling anisotropic growth and emission wavelength shifting is demonstrated. The synthesized Cs₅ Cu₃ Cl₆ I₂ NCs have an excellent photoluminescence (PL) retention rate, even at high temperature, and exhibit high stability over multiple heating-cooling cycles under ambient conditions. Moreover, under 850-nm femtosecond laser irradiation, the NCs exhibit three-photon absorption (3PA)-induced PL, highlighting the possibility of utilizing their nonlinear optical properties. Such thermally stable and highly luminescent Cs₅ Cu₃ Cl₆ I₂ NCs with nonlinear optical properties overcome the limitations of conventional blue-emitting nanomaterials. These findings provide insights into the mechanism of the colloidal synthesis of Cs₅ Cu₃ Cl₆ I₂ NCs and a foundation for further research.

Recent developments in lead-free bismuth-based halide perovskite nanomaterials for heterogeneous photocatalysis under visible light

Halide perovskite materials, especially lead-based perovskites, have been widely used for optoelectronic and catalytic applications. However, the high toxicity of the lead element is a major concern that directs the research work toward lead-free halide perovskites, which could utilize bismuth as a promising candidate. Until now, the replacement of lead by bismuth in perovskites has been well studied by designing bismuth-based halide perovskite (BHP) nanomaterials with versatile physical-chemical properties, which are emerging in various application fields, especially heterogeneous photocatalysis. In this mini-review, we present a brief overview of recent progress in BHP nanomaterials for photocatalysis under visible light. The synthesis and physical-chemical properties of BHP nanomaterials have been comprehensively summarized, including zero-dimensional, two-dimensional nanostructures and hetero-architectures. Later, we introduce the photocatalytic applications of these novel BHP nanomaterials with visible-light response, improved charge separation/transport and unique catalytic sites. Due to advanced nano-morphologies, a well-designed electronic structure and an engineered surface chemical micro-environment, BHP nanomaterials demonstrate enhanced photocatalytic performance for hydrogen generation, CO₂ reduction, organic synthesis and pollutant removal. Finally, the challenges and future research directions of BHP nanomaterials for photocatalysis are discussed.

Metal-Organic Framework Materials in Perovskite Solar Cells: Recent Advancements and Perspectives

Organic-inorganic hybrid perovskite solar cells (PSCs) are among the most promising candidates for the next generation of photovoltaic devices because of the significant increase in their power conversion efficiency (PCE) from less than 10% to 25.7% in past decade. The metal-organic framework (MOF) materials owing to their unique properties, such as large specific surface area, abundant binding sites, adjustable nanostructures, and synergistic effects, are used as additives or functional layers to enhance the device performance and long-term stability of PSCs. This review focuses on the recent advancements in the applications of MOFs as/in different functional layers of PSCs. The photovoltaic performance, impact, and advantages of MOF materials integrated into the perovskite absorber, electron transport layer, hole transport layer, and interfacial layer are reviewed. In addition, the applicability of MOFs to mitigate leakage of Pb²⁺ from halide perovskites and corresponding devices is discussed. This review concludes with the perspectives on further research directions for employing MOFs in PSCs.

Room temperature nondestructive encapsulation via self-crosslinked fluorosilicone polymer enables damp heat-stable sustainable perovskite solar cells

Encapsulation engineering is an effective strategy to improve the stability of perovskite solar cells. However, current encapsulation materials are not suitable for lead-based devices because of their complex encapsulation processes, poor thermal management, and inefficient lead leakage suppression. In this work, we design a self-crosslinked fluorosilicone polymer gel, achieving nondestructive encapsulation at room temperature. Moreover, the proposed encapsulation strategy effectively promotes heat transfer and mitigates the potential impact of heat accumulation. As a result, the encapsulated devices maintain 98% of the normalized power conversion efficiency after 1000 h in the damp heat test and retain 95% of the normalized efficiency after 220 cycles in the thermal cycling test, satisfying the requirements of the International Electrotechnical Commission 61215 standard. The encapsulated devices also exhibit excellent lead leakage inhibition rates, 99% in the rain test and 98% in the immersion test, owing to excellent glass protection and strong coordination interaction. Our strategy provides a universal and integrated solution for achieving efficient, stable, and sustainable perovskite photovoltaics.

Well-Defined Fullerene Bisadducts Enable High-Performance Tin-Based Perovskite Solar Cells

Tin-based perovskite solar cells (TPSCs) are attracting intense research interest due to their excellent optoelectric properties and eco-friendly features. To further improve the device performance, developing new fullerene derivatives as electron transporter layers (ETLs) is highly demanded. Four well-defined regioisomers (trans-2, trans-3, trans-4, and e) of diethylmalonate-C₆₀ bisadduct (DCBA) are isolated and well characterized. The well-defined molecular structure enables us to investigate the real structure-dependent effects on photovoltaic performance. It is found that the chemical structures of the regioisomers not only affect their energy levels, but also lead to significant differences in their molecular packings and interfacial contacts. As a result, the devices with trans-2, trans-3, trans-4, and e as ETLs yield efficiencies of 11.69%, 14.58%, 12.59%, and 10.55%, respectively, which are higher than that of the as-prepared DCBA-based (10.28%) device. Notably, the trans-3-based device also demonstrates a certified efficiency of 14.30%, representing one of the best-performing TPSCs.

Synthesis of Efficient and Stable Tetrabutylammonium Copper Halides with Dual Emissions for Warm White Light-Emitting Diodes

In order to achieve a high color-rendering index (CRI) and low correlated color temperature (CCT) indoor lighting, single-component phosphors with broad-band dual emission are in high demand for white-light-emitting diodes (WLEDs). However, phosphors with such fluorescent properties are rare at present. Herein, we report a facile solid-state chemical method for the synthesis of single-component phosphor with broad-band emission and a large Stokes shift that can meet the requirements of future white-light sources. These new tetrabutylammonium copper halides phosphors have excellent warm white emission characteristics, and their luminescence peaks are located at 494 and 654 nm. The optimized photoluminescence (PL) quantum yield can reach 93.7 %. The typical CIE coordinate of the as-fabricated WLED is at (0.3620, 0.3731) with a CRI of 89 and low CCT of 4516 K.

Ultraviolet photodetector based on RbCu2I3microwire

Copper-based halide perovskites have shown great potential in lighting and photodetection due to their excellent photoelectric properties, good stability and lead-free nature. However, as an important piece of copper-based perovskites, the synthesis and application of RbCu₂I₃have never been reported. Here, we demonstrate the synthesis of high-quality RbCu₂I₃microwires (MWs) by a fast-cooling hot saturated solution method. The prepared MWs exhibit an orthorhombic structure with a smooth surface. Optical measurements show the RbCu₂I₃MWs have a sharp ultraviolet absorption edge with 3.63 eV optical band gap and ultra-large stokes shift (300 nm) in photoluminescence. The subsequent photodetector based on a single RbCu₂I₃MW shows excellent ultraviolet detection performance. Under the 340 nm illumination, the device shows a specific detectivity of 5.0 × 10⁹Jones and a responsivity of 380 mA·W^-1. The synthesis method and physical properties of RbCu₂I₃could be a guide to the future optoelectronic application of the new material.

Solvent-Type Passivation Strategy Controls Solid-State Self-Quenching-Resistant Behavior in Sulfur Dots

Treatment of sulfur dots with polyethylene glycol (PEG) has been an efficient way to achieve a high luminescence quantum yield, and such a PEG-related quantum dot (QD)-synthesis strategy has been well documented. However, the polymeric insulating capping layer acting as the "thick shell" will significantly slow down the electron-transfer efficiency and severely hamper its practical application in an optoelectric field. Especially, the employment of synthetic polymers with long alkyl chains or large molecular weights may lead to structural complexity or even unexpected changes of physical characteristics for QDs. Therefore, in sulfur dot preparation, it is a breakthrough to use short-chain molecular species to replace PEG for better control and reproducibility. In this article, a solvent-type passivation (STP) strategy has been reported, and no PEG or any other capping agent is required. The main role of the solvent, ethanol, is to directly react with NaOH, and the generated sodium ethoxide passivates the surface defects. The afforded STP-enhanced emission sulfur dots (STPEE-SDs) possess not only the self-quenching-resistant feature in the solid state but also the extension of fluorescence band toward the wavelength as long as 645 nm. The realization of sulfur dot emission in the deep-red region with a decent yield (8.7%) has never been reported. Moreover, a super large Stokes shift (300 nm, λ_ex = 345 nm, λ_em = 645 nm) and a much longer decay lifetime (109 μs) have been found, and such values can facilitate to suppress the negative influence from background signals. Density functional theory demonstrates that the surface passivation via sodium ethoxide is dynamically favorable, and the spectroscopic insights into emission behavior could be derived from the passivation effect of the sulfur vacancy as well as the charge-transfer process dominated by the highly electronegative ethoxide layer.

A Forest-Based Triboelectric Energy Harvester

Triboelectric nanogenerators (TENGs) are a new class of energy harvesting devices that have the potential to become a dominating technology for producing renewable energy. The versatility of their designs allows TENGs to harvest mechanical energy from sources like wind and water. Currently used renewable energy technologies have a restricted number of materials from which they can be constructed, such as metals, plastics, semiconductors, and rare-earth metals. These materials are all non-renewable in themselves as they require mining/drilling and are difficult to recycle at end of life. TENGs on the other hand can be built from a large repertoire of materials, including materials from bio-based sources. Here, a TENG constructed fully from wood-derived materials like lignin, cellulose, paper, and cardboard, thus making it 100% green, recyclable, and even biodegradable, is demonstrated. The device can produce a maximum voltage, current, and power of 232 V, 17 mA m-2, and 1.6 W m-2, respectively, which is enough to power electronic systems and charge 6.5 µF capacitors. Finally, the device is used in a smart package application as a self-powered impact sensor. The work shows the feasibility of producing renewable energy technologies that are sustainable both with respect to their energy sources and their material composition.

Phonon-Mediated Slow Hot Carrier Dynamics in Lead-Free Cs3Bi2I9 Perovskite Single Crystal

In this report, we study the hot carrier cooling mechanism of the Cs3Bi2I9 single crystal by using femtosecond transient reflectance (fs-TR) spectroscopy. We find an unusual slow hot carrier cooling associated with longitudinal optical (LO) and coherent longitudinal acoustic phonons (CLAPs) emission during the deexcitation of the hot carriers. We posit the interplay between the hot-carriers and the LO and CLA phonons in subpicosecond to subnanosecond time scales, respectively, by analyzing the TR kinetics upon perturbation with excess energy. Furthermore, we measured the CLAPs propagation velocity in Cs3Bi2I9, the crystal, ranging from 1820 to 2000 ms-1. The elastic constants and frequency of Brillouin oscillations were estimated as 20.08 GPa and 14.66 GHz, respectively. Our discovery delivers new physical insights into how the hot carriers in Cs3Bi2I9 single crystal are coupled with a crystal lattice that controls the hot carrier dynamics.

Recent advances in lead-free double perovskites for x-ray and photodetection

Over the last decade, lead halide perovskites have attracted significant research attention in the field of photovoltaics, light-emitting devices, photodetection, ionizing radiation detection, etc, owing to their outstanding optoelectrical properties. However, the commercial applications of lead-based perovskite devices are restricted due to the poor ambient stability and toxicity of lead. The encapsulation of lead-based devices can reduce the possible leakage of lead. However, it is hard to ensure safety during large-scale production and long-term storage. Recently, considerable efforts have been made to design lead-free perovskites for different optoelectronic applications. Metal halide double perovskites with the general formula of A₂M^IM^IIIX₆or A₂M^IVX₆could be potentially considered as green and stable alternatives for different optoelectronic applications. In this review article, we focus on the recent progress and findings on lead-free halide double perovskites for x-ray and UV-vis photodetection applications. Lead-free halide double perovskite has recently drawn a great deal of attention for superior x-ray detection due to its high absorption coefficient, large carrier mobility-lifetime product, and large bulk resistance. In addition, these materials exhibit good performance in photodetection in the UV-vis region due to high photocarrier generation and efficient carrier separation. In this review, first, we define the characteristics of lead-free double perovskite materials. The fundamental characteristics and beneficial properties of halide perovskites for direct and indirect x-ray detection are then discussed. We comprehensively review recent developments and efforts on lead-free double perovskite for x-ray detection and UV-vis photodetection. We bring out the current challenges and opportunities in the field and finally present the future outlook for developing lead-free double perovskite-based x-ray and UV-vis photodetectors for practical applications.