Key Takeaways & Executive Findings
- •• • DHIII and ThPyI organic spacer cations induce spontaneous formation of stable buried 2D perovskites, resisting dissolution during subsequent 3D perovskite spin-coating and thermal annealing, ensuring structural integrity and reproducible templating. • • The buried 2D perovskite layer acts as a crystallization template, yielding larger and more uniform 3D perovskite grains, as evidenced by SEM and GIWAXS analyses, reducing defect states and non-radiative recombination. • • Photoluminescence spectra from both perovskite and glass sides confirm improved crystallization uniformity and defect passivation at the buried interface, directly addressing the performance-limiting factor in PSCs. • • This approach mitigates residual strain at the buried interface, which is critical for long-term device stability, as strain-induced defects are a major degradation pathway.
Abstract
Perovskite solar cells (PSCs) are leading candidates in third-generation photovoltaics, yet achieving uniform crystallization from top to buried interfaces remains critical for high efficiency and stability. The buried interface is particularly challenging due to substrate-induced nucleation suppression and spatial confinement, leading to disordered crystallization, small grains, and high defect densities. Residual strain from thermal expansion mismatch further exacerbates defect formation and non-radiative recombination. Existing strategies, such as heterogeneous nucleation sites or pre-deposited 2D perovskite seeds, often fail because these layers are washed away or dissolved during subsequent processing, compromising structural integrity and reproducibility. In a recent breakthrough, Chen et al. (2025) reported the construction of stable buried 2D perovskites using specially designed organic spacer cations: 2,3-dihydroisoindole hydroiodide (DHIII) and 4,5,6,7-tetrahydrothieno[3,2-c]pyridine hydroiodide (ThPyI). Unlike conventional spacers like phenethylammonium (PEA) and 2-thiophenemethylammonium (ThMA), DHIII and ThPyI induce spontaneous formation of 2D perovskites that remain stable during subsequent spin-coating and annealing. This buried 2D structure effectively templates the growth of high-quality 3D perovskites, improving crystallization uniformity and passivating defects. The work demonstrates a viable route to overcome the long-standing challenge of stabilizing 2D phases at the buried interface, potentially enabling more efficient and stable PSCs.
1. Introduction
The buried interface in perovskite solar cells remains the most formidable barrier to achieving both high efficiency and long-term operational stability. Unlike the top interface and bulk, where additive engineering and interface modification have proven effective, the buried interface suffers from substrate-induced nucleation suppression and spatial confinement, leading to disordered crystallization, small grain sizes, and high defect densities. Furthermore, thermal expansion mismatch between the perovskite and substrate generates residual strain, which exacerbates defect formation and non-radiative recombination, ultimately degrading device performance. Conventional strategies, such as pre-depositing 2D perovskite seeds or using heterogeneous nucleation sites, have shown promise but are fundamentally limited: these pre-formed layers are often washed away or dissolved by the solvent during subsequent spin-coating of the 3D perovskite solution or thermal annealing, resulting in uncontrollable distribution of the 2D phase and irreproducible growth.
Chen et al. have now reported a breakthrough that directly addresses this bottleneck by employing specially designed organic spacer cations—2,3-dihydroisoindole hydroiodide (DHIII) and 4,5,6,7-tetrahydrothieno[3,2-c]pyridine hydroiodide (ThPyI)—which spontaneously form stable 2D perovskites at the buried interface. Unlike conventional spacers such as PEA and ThMA, these cations induce 2D phases that remain intact throughout subsequent processing, providing a reliable template for the growth of high-quality 3D perovskites. This dynamic assembly approach not only improves crystallization uniformity and passivates defects but also mitigates residual strain, offering a practical solution to a long-standing challenge in PSC fabrication.
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Liyan Yang, Tao Wang (2026). Dynamic assembly stabilizes buried 2D perovskite. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3909-0
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Frequently Asked Questions
What specific mechanisms allow DHIII and ThPyI to form stable 2D perovskites at the buried interface, and how do they resist dissolution during subsequent processing?
DHIII and ThPyI are designed with rigid, cyclic structures that enhance intermolecular interactions and coordination with the perovskite lattice, leading to spontaneous formation of 2D phases with high binding energy. Their hydrophobic nature and strong interaction with the substrate prevent dissolution by the polar solvents used in 3D perovskite precursor solutions. This stability is confirmed by the persistence of the 2D phase after spin-coating and annealing, as evidenced by GIWAXS and PL measurements.
How does the buried 2D perovskite layer influence the crystallization kinetics of the 3D perovskite, and what are the resulting grain size and defect density improvements?
The 2D layer acts as a heterogeneous nucleation template, reducing the energy barrier for nucleation and promoting oriented growth of the 3D perovskite. This leads to larger, more uniform grains with fewer grain boundaries, as observed in SEM images. Defect passivation is achieved through the coordination of the spacer cations at the interface, reducing non-radiative recombination, as indicated by enhanced photoluminescence intensity and longer carrier lifetimes.
What is the impact of this approach on the residual strain at the buried interface, and how does it correlate with long-term device stability?
The 2D perovskite layer accommodates the thermal expansion mismatch between the perovskite and substrate, reducing residual strain. This is critical because strain-induced defects are a major cause of ion migration and degradation. By mitigating strain, the approach enhances the operational stability of PSCs, as evidenced by improved retention of efficiency under continuous illumination and thermal cycling.
How does the performance of DHIII/ThPyI-based devices compare to those using conventional spacers like PEA or ThMA, in terms of efficiency and reproducibility?
Devices incorporating DHIII/ThPyI show higher power conversion efficiencies due to improved crystallization and reduced non-radiative recombination. The stability of the 2D phase ensures reproducible device performance across batches, addressing the irreproducibility issues seen with PEA or ThMA, which often suffer from dissolution and uncontrolled distribution.
What are the scalability prospects of this buried 2D perovskite approach for industrial-scale manufacturing?
The approach is compatible with standard solution-processing methods, such as spin-coating, which are already used in lab-scale and pilot-scale production. The key advantage is the spontaneous formation of the 2D layer without additional complex steps, simplifying the fabrication process. However, further optimization is needed to ensure uniformity over large areas and to assess the cost-effectiveness of the spacer cations.
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