In the realm of perovskite solar cells, the evolution toward higher efficiency and enhanced stability remains a paramount goal for researchers worldwide. Recently, a pioneering advancement has emerged from efforts to engineer the interface between the perovskite active layer and the electron transport layer, utilizing an innovative buried 2D/3D heterojunction formed via a solid-state ligand-exchange reaction. This breakthrough heralds a new chapter in perovskite solar cell technology, offering pathways to unprecedented power conversion efficiencies and device robustness.
At the core of this development lies the intricate manipulation of two-dimensional (2D) and three-dimensional (3D) perovskite phases within the solar cell architecture. Traditionally, 2D perovskite layers have been introduced at either the bulk or surface of 3D perovskite films by adding long-chain ammonium salts during fabrication. While these 2D structures are recognized for enhancing device stability and passivating surface defects, the challenge has been to precisely localize them exclusively at the buried bottom interface without adversely affecting the bulk properties of the perovskite layer.
The team tackled this challenge by exploiting a novel approach involving sequential grafting of thioglycolic acid and oleylamine onto SnO₂ nanoparticles—the commonly used electron transport layer in n–i–p configured solar cells. The ligand chemistry was meticulously designed to anchor the oleylamine tightly via strong chemical bonds with thioglycolic acid. This chemistry effectively controls the interfacial cation exchange with formamidinium iodide (FAI), a crucial perovskite precursor, ensuring that 2D phase formation occurs selectively and only after thermal annealing during device processing.
This selective in situ formation of the 2D perovskite layer creates a well-defined buried 2D/3D heterojunction at the interface between SnO₂ and the 3D FA-based perovskite absorber. The presence of this localized 2D layer catalyzes the crystallization kinetics of the 3D perovskite phase, yielding larger grains and a more uniform film morphology. Such improved crystallinity is pivotal for reducing recombination losses, enhancing charge carrier mobility, and ultimately boosting the device’s photovoltaic performance.
Moreover, this buried heterojunction substantially diminishes defect densities at the electron transport interface. Defects typically act as nonradiative recombination centers that degrade performance and accelerate device aging. By achieving over a tenfold reduction in defect concentration at this critical juncture, the researchers effectively curtailed interfacial recombination pathways, thereby extending both the efficiency and operational stability of the solar cells.
The benefits of this interfacial engineering are reflected in the impressive power conversion efficiencies achieved by the resulting perovskite solar cells. Devices fabricated on a small active area (0.09 cm²) reached an outstanding certified efficiency of 26.04%, a benchmark competitive with the highest-performing perovskite architectures to date. Notably, this method scales favorably, maintaining robust efficiencies of 23.44% and 22.22% on larger aperture areas of 21.54 cm² and 64.80 cm², respectively, demonstrating promising prospects for commercial viability and large-scale deployment.
This advancement also underscores a vital understanding of the interfacial chemistry in perovskite solar cells. The utilization of a solid-state ligand-exchange reaction for interfacial modification diverges from conventional solution-processed routes, offering enhanced control and stability. The thermal annealing step triggers the cation exchange precisely, enabling the formation of reproducible, high-quality 2D/3D heterostructures that resist decomposition and ion migration under operational stresses.
The approach opens new frontiers in perovskite interface research, where chemical tailoring of transport layers and their interactions with perovskite precursors can be harnessed for optimized device architectures. By integrating chemically robust ligands and leveraging solid-state reactions, the strategy holds promise for overcoming key barriers that have dogged perovskite solar cells, particularly regarding long-term durability and consistent high performance.
In practical terms, the buried 2D layer serves as an energy cascade or passivation buffer layer, minimizing energetic disorder at the interface and facilitating efficient extraction of photogenerated electrons into the SnO₂ layer. This design mitigates interfacial energy barriers and suppresses charge carrier recombination, which are critical for achieving maximal photocurrent and fill factor in perovskite solar cells.
Furthermore, since SnO₂ is widely recognized for its excellent electron transport properties and chemical stability, the functionalization approach demonstrated here can be seamlessly integrated into existing manufacturing processes. Such compatibility accelerates the potential translation of this technology from laboratory-scale innovations to industrial-scale photovoltaic module production.
The researchers’ methodology also sparks possibilities for customizing interface chemistry for various perovskite compositions beyond formamidinium-based systems. Fine-tuning ligand identities and processing conditions could unlock similar buried heterojunction benefits for mixed-cation or mixed-halide perovskites, thereby expanding the versatility of this technique across the perovskite family.
In essence, this work represents a critical stride toward the long-sought goal of creating perovskite solar cells that combine efficiency, scalability, and operational longevity. The judicious engineering of a buried 2D/3D heterojunction via a solid-state ligand-exchange reaction stands as an elegant solution to interfacial challenges, paving a route toward the widespread deployment of perovskite photovoltaics in the global energy landscape.
As the solar industry advances toward a sustainable, carbon-neutral future, innovations like this herald transformative impacts, enabling low-cost, highly efficient, and durable solar technologies. Continued exploration of interface chemistry and materials engineering is poised to unlock further enhancements, bringing perovskite solar cells closer to their theoretical efficiency limits and widespread commercial success.
With this breakthrough, the collaboration of material chemists, physicists, and device engineers demonstrates the power of interdisciplinary research to solve complex challenges in renewable energy technologies. The interplay between molecular-level control and macroscopic device performance highlights the sophisticated science behind next-generation photovoltaics.
Looking ahead, the implications of buried 2D/3D heterojunctions extend beyond solar cells alone. Similar interfacial strategies could be adapted for light-emitting diodes, photodetectors, and other optoelectronic devices where controlling charge transport and defect densities at interfaces is crucial. This versatility suggests a broad impact across emerging semiconductor technologies.
Ultimately, this research embodies a visionary approach to tackling fundamental materials limitations through chemical precision and innovative processing, setting a benchmark for future explorations in perovskite and hybrid semiconductor interfaces.
Subject of Research: Perovskite solar cells, interface engineering, 2D/3D heterojunctions, solid-state ligand-exchange, SnO₂ electron transport layers, perovskite crystallization and defect passivation.
Article Title: Buried 2D/3D heterojunction in n–i–p perovskite solar cells through solid-state ligand-exchange reaction
Article References:
Zhao, Q., Zhang, B., Hui, W. et al. Buried 2D/3D heterojunction in n–i–p perovskite solar cells through solid-state ligand-exchange reaction. Nat Energy (2026). https://doi.org/10.1038/s41560-026-01980-4
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