Atomic Layer Deposition of CsI and CsPbI₃

Cesium iodide (CsI) is a well-established scintillator material that also serves as a precursor for all-inorganic halide perovskite solar absorbers, such as CsPbI3. However, the lack of conformal and scalable methods to deposit halide perovskite thin films remains a major challenge on their way to commercialization. In this work, we employ atomic layer deposition (ALD) as the key method due to its inherent scalability to large areas and complex-shaped surfaces. We demonstrate two new ALD processes for the deposition of CsI and CsPbI3 thin films. The CsI process relies on cesium bis(trimethylsilyl) amide (Cs(btsa)) and tin(IV) iodide (SnI4) as precursors and yields high-purity, uniform, and phase-pure thin films. This process works in a wide temperature range (140-350 degrees C) and exhibits a large growth per cycle value (GPC) of 3.3 angstrom (85% of a CsI monolayer). Furthermore, we convert CsI into CsPbI3 perovskite by exposing a CsI film to our earlier PbI2 ALD process. We demonstrate the deposition of phase-pure gamma- or delta-CsPbI3 perovskite thin films, depending on the applied deposition temperature and number of PbI2 cycles. We believe that the ALD-based approach described in this work will offer a viable alternative for depositing perovskite thin films in applications that involve complex high aspect ratio structures or large substrate areas.