 perovskite containing solar cells can be fabricated using a two-step process involving spin coating of lead iodide followed by dipping in a solution of methyl ammonium iodide. The dipping time affects the device's performance, with longer dipping times resulting in higher current densities and voltages. Remnant lead iodide is found to act as a blocking layer, reducing charge recombination and increasing the device's efficiency. Additionally, increased dipping time results in larger perovskite crystal sizes at the whole transporting material interface, leading to improved device performance. This article was authored by D&H Chao, Konstantinos C. Stumpos, Christos D. Maliakas, and others.