Hybrid organic–inorganic halide perovskites have attracted considerable attention as photoabsorber materials for next-generation photovoltaic and optoelectronic devices owing to their excellent optoelectronic properties. Among vacuum deposition techniques, RF magnetron sputtering offers advantages including large-area scalability, high film uniformity, and solvent-free processing. However, direct sputtering of stoichiometric MAPbI₃ remains challenging because plasma-induced iodine loss inevitably produces PbI₂-rich films. Moreover, the decomposition pathway governing compositional evolution during sputtering remains poorly understood, hindering the development of effective all-vacuum strategies.^[1,2]

To investigate this issue, a 3-inch unsintered MAPbI₃ sputtering target was fabricated from high-quality single-phase MAPbI₃ crystals synthesized by an antisolvent vapor-assisted crystallization process. The crystals exhibited a Pb atomic ratio of approximately 1:3.3, characteristic tetragonal MAPbI₃ diffraction peaks, an optical bandgap of 1.52 eV, and a strong photoluminescence peak at 780 nm, confirming their high structural and optoelectronic quality. The crystal-derived target also maintained stable RF magnetron sputtering without macroscopic fracture. Despite stable plasma discharge, the deposited films consistently exhibited PbI₂-rich characteristics. As the film thickness increased, the I/Pb atomic ratio gradually decreased from approximately 2.4 to 2.0, indicating progressive iodine depletion. Structural, compositional, and optical analyses revealed that the highly non-equilibrium RF plasma simultaneously induces energetic ion bombardment and plasma-emitted photon irradiation, selectively removing volatile MAI-derived species while preferentially transporting less volatile Pb–I species to the growing film. This imbalance in the sputtered flux ultimately results in PbI₂-rich film formation. Based on these observations, a plasma-induced coupled decomposition mechanism is proposed to explain the compositional evolution during MAPbI₃ sputtering and provide a mechanistic framework for an effective recovery process.^[3]

Guided by this mechanistic understanding, a Species Replenishment System (SRS) was developed to precisely deliver MAI vapor under vacuum conditions. Using the SRS, a Species Replenishment Process (SRP) was performed by exposing sputtered PbI₂-rich films to controlled MAI vapor to compensate for plasma-induced iodine deficiency and replenish volatile MA-derived species. The SRP restored the stoichiometric composition and converted the PbI₂-rich films into the MAPbI₃ phase without solution processing. X-ray diffraction (XRD) confirmed recovery of the characteristic MAPbI₃ phase through the reappearance of the diffraction peaks at 14.1° and 28.4°, while the I/Pb atomic ratio increased to a nearly stoichiometric value of 2.99. The optical bandgap also recovered to 1.58 eV, demonstrating restoration of both the chemical composition and optoelectronic properties. These results demonstrate that the SRP provides an effective vacuum-compatible strategy for converting plasma-degraded PbI₂-rich films into stoichiometric MAPbI₃ absorber layers.

Overall, this study provides mechanistic insight into plasma-induced decomposition during RF magnetron sputtering of hybrid perovskites and establishes the SRS and its associated SRP as an effective all-vacuum platform for restoring stoichiometric MAPbI₃ thin films. The proposed strategy offers a practical pathway toward scalable fabrication of high-quality perovskite absorber layers for next-generation photovoltaic and optoelectronic applications.