Effects of Pressure on Optoelectronic Properties of Perovskite Thin Films Fabricated via Radio Frequency Sputtering

Perovskite thin films were fabricated via the radio frequency (RF) sputtering process, which could provide great control over the crystal structure and uniformity of the films. Lead sulfide was chosen as a precursor for the lead source and further converted to lead iodide (RF-PbI₂) and methylammonium lead iodide (RF-CH₃NH₃PbI₃: RF-MAPbI₃) through a two-step gas-phase reaction. The sputtering pressure was varied from 0.3 to 0.9 Pa to investigate its influence on the characteristics of the RF-PbI₂ and RF-MAPbI₃ films. The increase in the pressure transformed the structure of the RF-PbI₂ films from a dense to porous structure; meanwhile, the grain growth behavior of the RF-MAPbI₃ was also observed after the conversion. Grain growth reduced the grain boundary density and decreased carrier trapping. This reduction of grain boundaries also enhanced light scattering and improved the light-harvesting properties of the films, as confirmed by a higher absorption coefficient in the visible region. The decrease in the grain boundaries also reduced the recombination centers and improved the carrier lifetime. Nevertheless, RF-MAPbI₃ thin films fabricated with pressures exceeding 0.5 Pa presented a highly porous structure and poor crystallinity. Thus, these findings indicated an optimal pressure of 0.5 Pa for the RF-sputtered lead sulfide (RF-PbS) precursor that resulted in an optimal perovskite thin film prepared via this commercial method, indicating a promising pathway toward robust, controllable, and scalable perovskite optoelectronic devices.