Dual-Functional Formic Acid Directs α-Phase Perovskite Microcrystals From Industrial Precursors for High-Yield and...

The solution-based fabrication of perovskite solar cells (PSCs) typically relies on high-purity materials, the cost of which limits commercial scalability. Here, we report an efficient strategy for directly synthesizing FAPbI₃-based perovskite microcrystals (MCs) from industrial-grade precursors using formic acid (HCOOH) as a multifunctional additive and antisolvent in a synergistic process combining inverse temperature crystallization (ITC) and antisolvent-assisted precipitation. In situ grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis reveals that formate anions (HCOO^-) coordinate with Pb²⁺ to regulate crystallization, passivate structural defects, and promote the direct formation of α-FAPbI₃. An optimal HCOOH concentration (40%-60% v/v) was identified, achieving a high microcrystalline yield of 92.83% and effectively suppressing the formation of δ-FAPbI₃. However, concentrations exceeding this range (>80% v/v) disrupt the precursor stoichiometry, leading to PbI₂ impurity segregation. Thin films fabricated using the optimized microcrystals exhibited improved morphological uniformity, enhanced crystallinity, reduced nonradiative recombination losses, and extended charge carrier lifetimes. As a result, inverted-structure PSCs based on these MCs achieve a champion power conversion efficiency of 25.24% (0.07 cm²). This work presents a cost-effective and scalable route for producing high-quality perovskite materials and provides mechanistic insights into the dual functionality of HCOOH, offering valuable guidance for the advancement of low-cost, high-performance perovskite photovoltaic technologies.