Program-Modulated Kinetics of Perovskite-Film Growth by Molecular "Thruster" for High-Efficiency and Stable Perovskite Solar Cells.

The rapid reaction between lead iodide (PbI) and formamidinium iodide (FAI) complicates the fabrication of high-quality formamidinium lead iodide (FAPbI) films. Conventional methods, such as using nonvolatile small molecular additives to slow the reaction, often result in buried interfacial voids and molecule diffusion, compromising the devices' operational stability. In this study, we introduced a molecular "thruster"-a hypervalent iodine (III) compound with three carbonyl groups and a C-I bond-that possesses coordination and dissociation abilities, enabling programed modulation of perovskite-film growth kinetics. Initially, the three carbonyl groups coordinate with PbI to slow the reaction between FAI and PbI, preventing δ-phase formation. As temperature rises, the C-I bond dissociates, promoting perovskite growth and the dissociated product iodobenzene will promote solvent volatilization, thus avoiding buried interfacial voids. Another product, a carbene compound with eight lone pair electrons sufficiently passivate the undercoordinated Pb defects and anchors at grain boundaries without diffusion. Consequently, the resultant FAPbI film displays high-quality with enhanced phase purity, compact morphology, and reduced defects. Evidently, 0.062- and 1.004-cm pero-SCs achieve power conversion efficiencies (PCEs) of up to 26.06 % (25.79 % certified) and 24.65 %, respectively. This approach also controls perovskite-film growth on plastic substrates, resulting in flexible pero-SCs with an impressive PCE of 25.12 %.