At the heart of this advance lies the challenge of effectively integrating 2D layers atop a robust 3D inorganic perovskite framework, predominantly composed of cesium lead iodide (CsPbI₃). Conventional approaches have utilized organic spacer cations designed to cap the 3D perovskite surface and create a laminar 2D overlayer, which passivates surface defects and suppresses ion migration. However, the tightly bonded cesium cations within the inorganic matrix impede facile exchange or incorporation by these spacer molecules. Even in scenarios where 2D layers form, their structural integrity is undermined by heat-induced cation migration, leading to heterogeneous interfaces that degrade device performance over time. This intricate balance between interfacial chemistry and thermal stability forms the core problem Liu et al. address.
Through meticulous experimentation coupled with comprehensive surface and structural characterizations, the authors identify that the formation of 2D/3D heterostructures is fundamentally driven by the interactions between ammonium functional groups of the spacer cations and the lead–iodide octahedra unit, denoted as [PbI₆]⁴⁻, which constitute the backbone of the perovskite lattice. These localized electrostatic and hydrogen bonding interactions facilitate the anchoring and ordering of organic cations on the inorganic surface. Recognizing this, the team posited that fine-tuning these interactions at the molecular level could modulate cation interdiffusion rates, crucial for forming structurally coherent and thermally stable heterostructures.
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To intensify the interaction potential, the researchers introduced electron-withdrawing fluorine substituents onto the organic spacer cations. Such fluorination enhances the electron deficiency of the ammonium head groups, thereby strengthening their electrostatic affinity toward the [PbI₆]⁴⁻ octahedra. This chemical modification not only promotes more effective penetration of the organic cations into the inorganic lattice surface but also facilitates controlled intermixing rather than random migration or desorption. Their findings revealed that fluorinated cations exhibited superior interdiffusion dynamics, leading to the formation of uniform 2D layers that intimately interface with the 3D perovskite substrate.
Yet, formation alone does not guarantee stability. The notoriously volatile nature of surface-bound cations, especially under operationally relevant thermal stress, remains a formidable hurdle. Conventional spacers are prone to cation loss and rearrangement at elevated temperatures, contributing to morphological degradation and performance decline. By probing the desorption energy landscape through experimental and computational methods, Liu and colleagues discovered that anchoring groups on spacer cations play an indispensable role in stabilizing the heterostructure. Specifically, incorporating functional groups capable of forming multiple coordination bonds with lead centers doubled the cation desorption energy relative to traditional ammonium-only spacers. This molecular “anchor” effectively immobilizes the cations, severely limiting their thermal migration pathways.
An exemplary implementation of this concept was realized by integrating perfluoro-1,4-phenylene dimethanammonium cations into the CsPbI₃ system. The perfluorinated aromatic core not only endowed the molecule with strong electron-withdrawing character but also the dimethanammonium functional groups provided robust binding affinity to the inorganic lattice. The resulting 2D/3D heterostructures demonstrated unprecedented synergy: charge transport remained efficient due to the coherent interface, while thermal stability was markedly enhanced due to suppressed cation migration. Solar cells fabricated with these heterostructures achieved a champion power conversion efficiency of 21.6%, rivaling many state-of-the-art perovskite devices while exhibiting remarkable thermal operating stability, sustaining maximal power point output at 85 °C for nearly 1000 hours.
The implications of this study extend beyond mere material chemistry. First, it establishes a paradigm for rational molecular design where electronic properties of spacer cations can be chemically engineered to direct interfacial assembly and stability. Second, the anchoring group concept provides a generalizable blueprint to mitigate thermally induced ion migration, a pervasive degradation mechanism in halide perovskites. Third, by highlighting the paramount importance of entire cation structures (not just functional groups), the work inspires a holistic approach to perovskite surface passivation.
In dissecting the fundamental mechanisms, the authors employed advanced techniques such as in situ temperature-dependent X-ray diffraction, grazing incidence wide-angle X-ray scattering, and time-of-flight secondary ion mass spectrometry. These analyses detailed the crystalline evolution and cation spatial distributions under thermal stimulus, revealing that fluorinated and anchored cations maintained structural order where traditional spacers faltered. Complementary first-principles calculations elucidated the increased binding energies and energy barriers for cation desorption imparted by anchoring functionalities, corroborating experimental observations. This multi-dimensional approach exemplifies the merging of theoretical modeling and empirical verification essential for materials innovation.
Furthermore, charge carrier dynamics and recombination pathways were scrutinized through photoluminescence lifetime measurements and impedance spectroscopy. The improved passivation reduced trap-assisted recombination, partially explaining the enhanced device efficiencies. The intimate 2D/3D interface formed a graded potential landscape facilitating charge extraction without introducing significant energy barriers. This observation contradicts some earlier concerns that 2D layers could impede charge transport due to their wider bandgaps, suggesting the precise molecular engineering enabled optimal balance between passivation and conductivity.
This investigation also opens new avenues for exploring other functionalized spacer cations exploiting different chemical motifs for anchoring and electron modulation. While fluorination was pivotal in this work, other electron-withdrawing entities or multidentate binding groups could be tailored to further enhance stability or tune optoelectronic properties. The approach is applicable not only to CsPbI₃ but potentially other inorganic and hybrid perovskites, broadening its utility.
Moreover, stability tests conducted under continuous light and elevated temperature conditions simulate real-world stressors and demonstrate the practical endurance of the devices. The thermal robustness of these 2D/3D heterostructure devices contrasts favorably with previous state-of-the-art inorganic perovskites where rapid degradation curtailed operational lifetimes. Longevity under such rigorous conditions augurs well for commercial deployment, where stable power outputs over thousands of hours are imperative.
Despite the compelling advancements, challenges remain before commercialization. The synthesis and integration of specialized anchoring cations at scale must be optimized for cost-efficiency. Additionally, the environmental impact and recycling potential of fluorinated organic spacers warrant evaluation. Nonetheless, this study represents a substantial stride toward reconciling high efficiency with durable stability in inorganic perovskite photovoltaics.
In summary, the work by Liu et al. articulates a sophisticated molecular engineering strategy to surmount one of the most pressing issues in perovskite solar cell technology—cation migration-induced instability. By leveraging electron-withdrawing fluorination and introducing anchoring functional groups, they not only promote controlled 2D/3D heterostructure formation but also achieve robust thermal stabilization, culminating in record performances for inorganic perovskite solar modules. This breakthrough sets a new benchmark and inspires a methodological pathway for designing next-generation stable perovskite photovoltaics, a critical step toward their integration into the energy mix.
As the solar energy sector intensifies efforts to diversify and enhance renewable technologies, innovations such as these underscore the profound impact of fundamental chemical insights on device engineering. The coupling of molecular design principles with device-scale validation exemplifies the direction needed to emulate the commercial success of silicon photovoltaics while exploiting the unique advantages of perovskites. It is expected that this pioneering approach to cation interdiffusion control will catalyze further research, ultimately accelerating the transition of perovskite solar cells from laboratory curiosities to ubiquitous clean energy solutions.
Subject of Research: Inorganic perovskite solar cells and 2D/3D perovskite heterostructure formation and stabilization via cation interdiffusion control
Article Title: Cation interdiffusion control for 2D/3D heterostructure formation and stabilization in inorganic perovskite solar modules
Article References:
Liu, C., Yang, Y., Fletcher, J.D. et al. Cation interdiffusion control for 2D/3D heterostructure formation and stabilization in inorganic perovskite solar modules. Nat Energy (2025). https://doi.org/10.1038/s41560-025-01817-6
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Tags: 2D/3D perovskite heterostructuresadvancements in photovoltaic efficiencycation interdiffusion controlcesium lead iodide frameworkdurable implementation of perovskite technologyinorganic perovskite solar cellsion migration suppression techniqueslong-term operational stabilitynovel chemical strategies for photovoltaicsoptoelectronic properties of perovskitessurface defect passivation strategiesthermal stability of perovskite photovoltaics
