Unraveling the effect of working pressure on the morphological, structural, optical, and compositional properties of PbI₂ thin films deposited by RF magnetron sputtering

초록

Radio frequency (RF) magnetron sputtering is a vapor deposition technique known for its good step coverage, high material utilization, and industrial adaptability. However, its application in the deposition of lead iodide (PbI2), a key semiconductor in photovoltaic applications, has been underexplored. In this study, for the first time, the correlation between working pressure and film properties is demonstrated. The formation of metallic lead and severe iodine deficiency, reported as a flaw of sputtered PbI2 films, is revealed to occur at low working pressure around 2 mTorr. Increasing the pressure suppresses the re-sputtering of iodine, manipulating the properties of the films. As working pressure increases to 25 mTorr, the metallic lead diminishes and the atomic ratio (I/Pb) changes from 0.8 to 1.8. Thus, we propose a structure model of sputtered PbI2 depending on the working pressure, demonstrating that adjusting the pressure eliminates the previously reported drawbacks of sputtered films while maintaining a conformal coating. Moreover, we are the first to report that sputtered PbI2 can be converted into perovskite through the close-spaced sublimation. We believe this study will pave a way for accelerating research on the fabrication of PbI2 films via RF magnetron sputtering, a field with significant potential in industrial application.

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