Anti-solvent engineering to rapid purify PbI2 for efficient perovskite solar cells

The purity of PbI 2 plays a critical role in determining the performance, stability, and reproducibility of perovskite solar cells (PSCs). However, the cost of high-purity PbI 2 is much higher than that of low-purity, and even the expensive high-purity PbI 2 suffers from batch variance issues. Although several purification methods have been developed, the straightforward and rapid purification of PbI 2 remains a challenge. The solar cell efficiency achieved by previous direct purification of PbI 2 is much lower than the state-of-the-art value. Therefore, people still doubt whether the low-purity PbI 2 is eligible for the fabrication of efficient solar cells even after purification. Herein, we report an anti-solvent engineering strategy for the rapid and facile purification of low-purity PbI 2 , which allows us to efficiently eliminate both the insoluble and soluble impurities. Eventually, the formamidinium-cesium (FA 0.95 Cs 0.05 PbI 3 ) PSCs made from directly purified PbI 2 show much enhanced performance and reproducibility. A champion power conversion efficiency of 23.91% is realized, which is the highest value ever reported for PSCs made from purified low-purity PbI 2 . The in-depth PbI 2 purification mechanism is further discussed from the perspective of solvent-coordination and solvent–solvent interactions by combining the donor number (D N ) value of solvents and Hansen solution parameters. The results reveal that the weaker interaction between PbI 2 and solvent, together with the stronger interaction between solvent and anti-solvent, is crucial for achieving successful purification. This study not only provides a simple and rapid method for the purification of PbI 2 but also enhances our understanding of the selective crystallization of PbI 2 and perovskite by elucidating the solvate and de-solvation processes of PbI 2 within the perovskite precursor.