Bar Coating Process of Two-Dimensional Lead Iodide Perovskite Solar Cells: Effects of Vertical Orientation, Anisotropic Photoconductivity, and Conversion Time

Understanding the effects of process variables on the large-scale manufacturing of lead halide perovskite solar cells (PSCs) is crucial for their commercialization. In this study, we conducted a comparative analysis of four bar (blade) coating methods, along with thermal annealing or hot airflow, for two-dimensional (2D) Ruddlesden–Popper PSCs in the presence of ammonium chloride (NH 4 Cl) and potassium chloride (KCl) additives. Intriguingly, the anisotropic charge carrier mobilities evaluated via time-resolved microwave conductivity exhibited a linear correlation between anisotropy and power conversion efficiency (PCE), similar to the observations in spin-coated 2D PSCs. The best PCE of 12.15% was achieved by using the process involving a hot air flow after bar coating. Notably, there was a significant variation in PCE (3–12%) among the four methods, which strongly correlated with their conversion time, suggesting that slow film formation is key to achieving optimal performance. Our findings, combined with the evaluation of crystallite orientation using 2D grazing-incidence X-ray diffraction, provide a foundation for exploring large-scale 2D PSC production.