Atomic Layer Deposition and Pulsed Chemical Vapor Deposition of SnI2 and CsSnI3

Abstract

Halide perovskites, such as CsSnI3, are materials renowned for their exceptional optoelectronic properties. CsSnI3 stands out as a desirable choice for nontoxic and environmentally friendly absorber layers in perovskite solar cells (PSC) due to the absence of lead in its composition. However, the limited ability to deposit conformal and scalable halide perovskite thin films remains a significant obstacle to the wide commercialization of PSCs. In this study, we use atomic layer deposition (ALD) to tackle this obstacle. We present two new ALD processes: SnI2 and CsSnI3. The SnI2 process operates at low temperatures within a narrow range (75-100 °C) and has a growth per cycle (GPC) of 0.9 Å. By depositing ALD CsI and subsequently ALD SnI2 at different temperatures, we successfully obtain phase-pure γ-CsSnI3 films via a conversion reaction. Moreover, we demonstrate an alternative method for γ-CsSnI3 film deposition by replacing the ALD SnI2 with a pulsed chemical vapor deposition (pulsed CVD) SnI2 step. This pulsed CVD SnI2 step operates at temperatures compatible with the ALD CsI process, effectively making it a one-step process (effective GPC > 2.0 Å) compared to the ALD conversion while retaining its conformality characteristics.