Key Takeaways & Executive Findings
- •• A novel aqueous synthesis method enables direct formation of α-FAPbI3 microcrystals by heating the reaction system, overcoming the energy barrier that typically yields δ-phase. • The resulting α-FAPbI3 microcrystals exhibit superior phase purity, crystallinity, and minimal defect density, serving as high-quality precursors for perovskite films. • Combining these microcrystals with a green anti-solvent reduces nonradiative recombination, achieving a power conversion efficiency of 24.43% in ambient air. • This eco-friendly aqueous route offers significant potential for scalable, low-cost production of high-performance perovskite solar cells.
Abstract
Perovskite solar cells (PSCs) based on α-phase FAPbI3 (α-FAPbI3) microcrystals precursor outperform those with δ-phase microcrystals due to their superior crystallinity and fewer defects, making α-phase microcrystals precursor more advantageous for high-performance PSCs. However, most reported synthesis methods of perovskite microcrystals, especially for aqueous synthesis, fail to reach the energy threshold required for α-phase transformation and therefore exhibit the δ phase. In this study, we introduce a novel aqueous synthesis method to fabricate α-FAPbI3 microcrystals. Our approach overcomes the energy barrier by properly heating the reaction system, enabling the direct formation of α-FAPbI3 in water. This direct one-step aqueous synthesis route yields α-FAPbI3 microcrystals with superior phase purity, crystallinity, and minimal defect density. Combined with green anti-solvent, the high-quality α-FAPbI3 microcrystals serving as exceptional precursors endow perovskite films with reduced nonradiative recombination. The PSC achieves a remarkable power conversion efficiency (PCE) of 24.43%, which is one of the highest PCE reports for using the green anti-solvent in ambient air condition. This aqueous synthesis approach shows a significant potential for scalable production of high-performance PSCs.
1. Introduction
Perovskite solar cells (PSCs) based on α-phase formamidinium lead iodides (α-FAPbI3) have emerged as a prominent technology in the photovoltaic field due to their exceptional power conversion efficiency (PCE) and affordability [1–5]. The quality of FAPbI3 perovskite films is critically dependent on the quality of the precursors [6]; however, research on impurities and nonstoichiometric ratios in precursors remains somewhat limited. Impurities from formamidinium iodide (FAI) and lead iodide (PbI2), along with nonstoichiometric precursor ratios, can compromise the structural integrity of perovskite layers, hinder charge-carrier transport, and degrade PSC performance [7–9].
A promising approach to address these significant challenges is the redissolution strategy, which involves using pre-synthesized perovskite microcrystal powders as precursors for film fabrication [10–12]. These pre-synthesized microcrystals are capable of achieving an ordered crystal structure, a well-controlled stoichiometric ratio, and high reproducibility [13]. Notably, films produced through the redissolution process generally preserve the initial phase of the pre-synthesized crystals, highlighting the critical role of precursor quality in determining film quality and, consequently, the PCE of high-performance PSCs [14]. The α-FAPbI3 microcrystals form in an “external strain free” environment, resulting in better crystallinity and fewer defects, which are subsequently reflected in the properties of the thin films. The statistical analysis of the PCEs reveals a clear trend that PSCs based on α-FAPbI3 microcrystals outperform those based on δ-FAPbI3 microcrystals (Fig. S1) [12,15–18]. Nevertheless, conventional synthesis methods for these crystals, such as mechanochemistry, microwave irradiation, or wet chemistry with organic solvents [8,16,18–19], are costly and unsuitable for large-scale industrial production.
The aqueous synthesis method offers a low-cost, environmentally friendly alternative that can produce perovskite microcrystals with high phase purity and low impurity levels without sacrificing performance. Water, as a solvent for perovskite microcrystal synthesis, leverages its polarity, thermal stability, and simplified post-processing, all of which contribute to improved control over the synthesis process. Additionally, water’s environmental suitability makes it a preferred option for developing eco-friendly materials, potentially minimizing the hazardous waste associated with organic solvents. Originally proposed in 2016, the aqueous synthesis method for perovskite microcrystals has regained significant attention in recent years due to its exceptional performance in enhancing the efficiency of PSCs, advancements in material processing techniques, and growing environmental concerns [20–21]. However, all
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Yining Pan, Qiang Zeng, Linhong Li, Mingxin Deng, Xiaoyu Yang, Rongze Zheng, Xiang Liao, Mingjun Zhang, Fangyang Liu (2025). Aqueous route to α-FAPbI3 microcrystals for efficient perovskite solar cells. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3191-x
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Frequently Asked Questions
What is the main innovation of this paper?
The paper introduces a novel aqueous synthesis method that directly forms α-FAPbI3 microcrystals by heating the reaction system, overcoming the energy barrier that typically results in the δ-phase. This one-step, water-based approach yields high-quality microcrystals with superior phase purity and crystallinity.
How does the aqueous synthesis method benefit perovskite solar cells?
The α-FAPbI3 microcrystals produced via this method serve as exceptional precursors, leading to perovskite films with reduced nonradiative recombination. When combined with a green anti-solvent, the solar cells achieve a high power conversion efficiency of 24.43% in ambient air, demonstrating the method's potential for scalable production.
What are the advantages of using α-FAPbI3 microcrystals over δ-phase microcrystals?
α-FAPbI3 microcrystals exhibit better crystallinity and fewer defects compared to δ-phase microcrystals, which translates into higher-quality perovskite films and improved solar cell performance. The statistical analysis shows that PSCs based on α-phase microcrystals outperform those based on δ-phase.
Why is the aqueous synthesis method considered environmentally friendly?
The method uses water as the solvent instead of hazardous organic solvents, reducing toxic waste and environmental impact. It also offers a low-cost and scalable route for producing high-quality perovskite microcrystals, aligning with green chemistry principles.
What is the significance of achieving 24.43% PCE in ambient air?
Achieving a PCE of 24.43% in ambient air conditions is notable because it demonstrates that high-efficiency perovskite solar cells can be fabricated without the need for controlled inert atmospheres, simplifying manufacturing and reducing costs. This is one of the highest efficiencies reported for green anti-solvent processing in ambient air.
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