Gel-Derived Amorphous Precursor Enables Homogeneous Pure-Phase -FAPbI₃ Films for Efficient and Stable Perovskite Solar Cells

Pure-phase alpha-formamidinium lead iodide (alpha-FAPbI(3)) perovskite solar cells (PSCs) possess potential high efficiency because of suitable bandgap. However, achieving high-quality alpha-FAPbI(3) films during the spin-coating process is challenging without anti-solvent extraction, due to the spontaneous formation of the more stable delta-FAPbI(3) phase and the complexity of multi-component perovskite precursor solutions. Here a gel precursor with an amorphous structure to eliminate the need for anti-solvent extraction in achieving the homogeneous and highly oriented pure-phase alpha-FAPbI(3) is devised films. The incorporation of N,N '-dimethylpropyleneurea, and alkylammonium chloride results in extended iodoplumbate clusters in the perovskite precursor solution. In situ, spectroscopic analysis reveals that the emergence of the stable amorphous gel precursor during the initial solidification stage ensures a uniform solute distribution. This effectively prevents preferentially oriented growth in the crystal phase precursor, leading to a significant enhancement in film homogeneity. As a result, power conversion efficiencies of 24.17% for the PSC, and 19.3% for the module are achieved, along with superior operational stability, retaining 96.1% of their initial efficiency after 850 h at the maximum power point tracking. These demonstrate the best performance for the reported pure-phase alpha-FAPbI(3) PSCs without anti-solvent extraction, showing great promise for scalable manufacture.