Enhancing the Phase Crystallinity of Buried Layer Perovskites through Organic Salt Molecule‐Assisted Crystal Growth

The performance and stability of perovskite solar cells rely crucially on the purity of their active perovskite phase. While the two‐step method has emerged as a well‐known technique for fabricating high‐performance cells, it suffers from significant PbI 2 phase impurities at the buried layer due to inefficient diffusion of cationic molecules into the preprepared PbI 2 layer. Herein, a simple yet highly effective method is presented to boost phase purity within the buried layer by introducing formamidinium iodide (FAI) seed molecules into the underlying PbI 2 layer. X‐Ray diffraction analysis result reveals that this process significantly reduces the PbI 2 phase and enhances the purity of the perovskite's phase. It is also observed that this technique can produce perovskite layer with a remarkably smooth surface structure and large interconnected crystal grains, forming a continuous layer. These characteristics are subjected to further enhancement when hexamethylenetetramine molecules are concurrently introduced with FAI into the PbI 2 layer. Solar cells fabricated using this method, with an active area of 0.1 cm 2 , achieve a remarkable power conversion efficiency of up to 24.52% with V oc as high as 1.18 V, representing a substantial improvement over cells produced using the standard two‐step method, which attains only 22.18% efficiency. With its simple yet impactful approach, the present method should find widespread adoption in the production of high‐performance perovskite solar cells.