Optimization of Vapor Flow Geometry for the Deposition of Highly Uniform Perovskite Thin Films

초록

Organic-Inorganic Hybrid Perovskites (OIHPs) have great potential in photovoltaics (PVs), photodetectors, and light emitting diodes (LEDs) owing to their excellent optoelectronic properties. Currently, a majority of studies on perovskite thin-film fabrication are employing solution-based approaches (i.e., spin-coating), which have limitations in scalable production and suffer from reproducibility. While the vapor deposition method is promising to this end, regulating the as-grown film thickness and roughness over the whole substrate, a prerequisite for highly uniform optoelectronic performance, remains challenging. In this study, we report the optimization of the flow geometry of vapor precursors to grow high-quality OIHP thin films with uniform thickness over the substrate. By varying the substrate position (e.g., horizontal vs. vertical) relative to the flow direction of vapor precursors in the CVD tube system, we confirmed that the vertical substrate position yielded a more uniform and smooth deposition of the [0001]-oriented lead iodide (PbI2) primary layers than the horizontal position. Furthermore, the precursor flow simulation based on the computational fluid dynamics (CFD) calculation predicted that the distribution of substrate temperature and molecular transport within the flow boundary layer is more regulated for the vertical position. Interestingly, horizontal flow exhibited a higher degree of uniformity in converting the pregrown PbI2 layer into the CH3NH3PbI3 perovskite thin film via the vapor transport of methylammonium iodide (CH3NH3I), suggesting that the solid diffusion following intercalation of CH3NH3I to PbI2 layers dominates the conversion process. Our results present a systematic approach to optimizing the vapor-based fabrication of OIHP thin films for uniform optoelectronic properties and scalable production with high reproducibility.