Bioinspired “cage traps” for closed-loop lead management of perovskite solar cells under real-world contamination assessment

The global energy crisis necessitates the development of sustainable renewable energy technologies. Perovskite solar cells (PSCs) have emerged as a promising candidate due to their high efficiency and scalable fabrication. However, the intrinsic instability of PSCs, stemming from volatile organic cations and soft lattice properties, leads to decreased efficiency and operational stability issues. More critically, the decomposition of perovskite films under external stimuli (moisture, light, heat) can release toxic Pb-based compounds, posing significant environmental concerns. Current efforts to mitigate Pb leakage, such as encapsulation with materials like polyurethane, polyisobutylene, graphene, and Al2O3, or the use of semi-transparent Pb adsorbents, have limitations. Encapsulation layers may fail under stress, while semi-transparent adsorbents limit adsorption capacity due to thickness constraints. Existing chemical adsorption strategies, often employing cation exchange resins (CERs), create secondary pollution problems from hazardous waste disposal. Furthermore, laboratory assessments of Pb leakage don't accurately reflect real-world conditions, ignoring complex factors like organic composition and microorganisms. The need for a sustainable solution that addresses both Pb leakage during operation and the environmental impact of end-of-life PSCs remains a major obstacle to commercialization. This research seeks to address these critical challenges by developing a novel bioinspired approach to Pb capture and management within PSCs.

Previous research has focused on encapsulating PSCs to reduce Pb leakage. Various encapsulation materials, including polymers and inorganic materials, have been investigated, but these methods often fail to prevent Pb diffusion if the device is damaged. Chemical adsorption strategies using functional materials have also been explored, but these are often limited by optical transparency requirements or generate secondary pollution. Studies on assessing Pb leakage are typically conducted under simplified laboratory conditions, failing to replicate the complexities of real-world ecosystems. Bio-inspired materials are gaining interest in environmental remediation, but their application to PSCs for closed-loop lead management remains largely unexplored. The study of spider silk and its unique properties offers inspiration for designing advanced materials with high Pb capture capacity and environmental compatibility.

This study employed a biomimetic approach inspired by the structure and functionality of spider webs. A multifunctional mesoporous amino-grafted-carbon net, termed biomimetic cage traps (BCTs), was synthesized. The synthesis involved three stages: (1) Initial grinding of the mesoporous matrix (MM), (2) Ultrasound-assisted structural separation to enhance pore formation and increase surface area, and (3) Self-assembly grafting of ethylenediamine (EDA) molecules onto the activated MM using an ultrasonic-assisted method. This introduced functional groups (-CONH-R-NH2) capable of strong chemical chelation with Pb ions. The chemical structure and surface properties of the BCT were characterized using techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and 3D optical profilometry. The Pb capturing mechanism was investigated by analyzing the changes in FTIR and XPS spectra after PbI2 adsorption, supported by density functional theory (DFT) calculations of binding energies. The Pb adsorption kinetics were modeled using the Langmuir isothermal adsorption equation and the pseudo-second-order kinetic model. The Pb capturing capacity of BCT was evaluated under various conditions, including immersion in PbI2 solutions, and real-world scenarios simulating hail impact, acid rain, and immersion in Yellow River water and soil. Perovskite solar cells (PSCs) were fabricated using a two-step deposition method and encapsulated with BCT. The photovoltaic performance and long-term stability of the BCT-encapsulated PSCs were assessed by measuring current-voltage (J-V) curves, external quantum efficiency (EQE) spectra, and conducting stability tests under different conditions (temperature, humidity, light exposure). A closed-loop Pb management strategy was developed, comprising four stages: (1) Pb precipitation from a perovskite solution using BCT, (2) Pb adsorption onto BCT, (3) Pb desorption from BCT using nitric acid, and (4) PbI2 recycling and reuse in PSC fabrication. The purity and crystalline structure of the recycled PbI2 were characterized using XRD, Raman spectroscopy, and ICP-OES.

The synthesized BCT exhibited a significantly higher Pb adsorption capacity compared to the unmodified MM. FTIR and XPS analyses confirmed the successful grafting of EDA and the formation of -CONH-R-NH2 functional groups, which played a crucial role in chemical chelation. DFT calculations showed that the -CONH-R-NH2 group had a higher binding energy with Pb ions compared to -COOH or -NH2, further supporting the chelation mechanism. The adsorption process could be divided into three stages: a chemically dominated stage, a physically dominated stage (capillary adsorption), and an equilibrium stage. The pseudo-second-order kinetic model accurately described the adsorption process, indicating that chemisorption was the dominant mechanism. The BCT demonstrated exceptional Pb capture efficiency (up to 99.25%) even under harsh environmental conditions such as simulated hail and acid rain. Real-world assessment in Yellow River water and soil showed that BCT encapsulation significantly reduced Pb leakage from damaged PSCs compared to unencapsulated and glass-encapsulated PSCs. The BCT encapsulation did not negatively impact the photovoltaic performance of the PSCs, maintaining over 92% of the initial PCE for 1000 hours under 25 °C and 50% RH conditions. The closed-loop Pb management process successfully recovered PbI2 with a purity comparable to commercial 99.99% PbI2. The PSCs fabricated using the recycled PbI2 achieved a PCE of 22.08%, only slightly lower than those fabricated using fresh PbI2 (22.37%), demonstrating the feasibility of closed-loop Pb management.

This study successfully addressed the critical challenge of Pb leakage in PSCs by employing a bioinspired design. The BCTs, inspired by the spider web, offered a superior solution to traditional encapsulation and adsorption strategies. The synergistic combination of chemical chelation and physical adsorption resulted in a remarkably high Pb capture efficiency. The real-world assessment validated the BCTs' performance under challenging conditions, significantly reducing the environmental risk associated with Pb contamination. The successful implementation of a closed-loop Pb management process highlights the economic and environmental benefits of the BCTs. This approach promotes the sustainable and eco-friendly development of PSC technology. The findings not only provide a practical solution for mitigating Pb leakage in PSCs but also offer valuable insights into designing advanced materials for environmental remediation.

This research demonstrated a bioinspired solution for Pb leakage and management in perovskite solar cells. Biomimetic cage traps (BCTs) effectively capture Pb via chemical chelation and physical adsorption, showing excellent performance under real-world conditions. A closed-loop Pb management system was established, enabling Pb recovery and reuse with minimal compromise to PSC performance. Future work can focus on optimizing BCT synthesis and exploring other bio-inspired materials for improved performance and broader applications in environmental remediation.

While this study demonstrated high Pb capture efficiency and successful recycling, further research is needed to optimize the long-term durability of the BCTs under various environmental conditions. The scalability of the BCT synthesis and integration into PSC manufacturing processes should be investigated to facilitate commercialization. The long-term effects of the BCT on the perovskite layer's stability may need to be assessed in greater depth.