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Fully solution-processed phase-pure 3D/2D perovskite bilayer heterojunctions - Communications Chemistry
Driving the world with sunlight is beneficial to achieving carbon peak in 2030 and carbon neutrality in 2060 1 . It is of vital significance to develop efficient and stable photoelectric light-harvesting materials. Organic–inorganic metal halide perovskites have become a star material in the photovoltaic field due to their high optical absorption coefficient, tunable band gap, long carrier lifetimes, and low exciton binding energy. Within a decade, the highest certified efficiency of perovskite solar cells (PSCs) has rapidly increased to 25.7% 2 , which is comparable to that of monocrystalline silicon solar cells. However, the interface between a perovskite and a charge transfer layer contains a high concentration of defects, which greatly reduces the long-term stability of PSCs 3 . Research endeavors are focused on the development of composition engineering 4 , additive engineering 5 , solvent engineering 6 , interfacial passivation 7 and processing methods 8 . In particular, 3D/2D perovskite bilayer heterojunctions have been widely shown to achieve efficient and stable PSCs by controlling interfacial defect density and energy band alignment at the interface of perovskite/charge transport layers 9 . However, it is challenging to control phase purity, film thickness, orientation, and crystal structure of 2D perovskites in traditional fabrication processes, i.e., by coating a 2D spacer (alkylammonium cation) solution on as-prepared 3D perovskite films (Fig.? 1A ). Meanwhile, the solvent of the 2D spacer (e.g., isopropanol) easily degrades the underlying 3D perovskite film.
Fig. 1: Preparation of 2D/3D perovskite bilayer heterojunctions and performance comparison of different methods and solvents. A Schematic illustration of preparing 3D/2D perovskite bilayer heterojunctions with different methods. B Comparison of different solvents based on dielectric constant (? r ) and Gutmann number (D N ). C Current–voltage curves of the champion 3D/2D perovskite bilayer heterojunction PSCs. D Stability assessment of the 3D/2D-based modules with different perovskite films at maximum power point tracking in an ambient atmosphere. A Adapted and ( B – D ) reproduced from Science 377 , 1425–1430 (2022). Reprinted with permission from AAAS.
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Writing in Science , a team led by Aditya Mohite from Rice University, USA, and Jacky Even from the University of Rennes, France, report a strategy to fabricate effective, ultrastable and phase-pure 3D/2D perovskite bilayer heterojunctions by directly coating single-crystal 2D perovskite inks on as-prepared 3D perovskite films ( https://www.science.org/doi/10.1126/science.abq7652 ) 10 . This strategy was realized by tailoring an orthogonal solvent system with a suitable dielectric constant (? r ) and Gutmann donor number (D N ) for dissolving 2D perovskite single crystals, while avoiding dissolution of the underlying 3D perovskite layer. “The biggest challenge was understanding the solvent interactions and solvation dynamics in order to find the right solvent”, comments Mohite. They found that the 2D perovskite single-crystal powders can be effectively dissolved without dissolving or degrading the underlying 3D perovskite film when ? r ?>?30 and 5 < D N ? “Scaling up of the 3D/phase-pure 2D bilayer structures should be the immediate step which will help to realize commercially viable perovskite solar cell modules,” explains Mohite. Their work indeed provides such a scalable solution-processing method to fabricate phase-pure, thick (>30?nm) and fully covered 2D perovskite interfacial layers. The strategy is also feasible in p-i-n devices, demonstrating its broad applicability. However, the growth mechanisms of phase-pure 2D perovskite upper layers and the crystal structures of the 3D/2D perovskite bilayer heterojunctions are still not entirely clear. Meanwhile, more in-depth research by a combination of interface engineering, composition engineering and solvent engineering should be conducted to achieve more efficient and operationally stable perovskite photovoltaics. .
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