Two-Step Processed Dion–Jacobson Perovskite for Enhancement of Solar Cell Efficiency and Stability

In this work, we demonstrate that the HTI (HTI = histammonium iodide) dication was incorporated into the PbI2 precursor solution to induce the preferred vertical orientation of the 2D Dion–Jacobson (DJ) perovskite film using a two-step deposition. 2D DJ (HTI) (FA)x(MA)1–xPbnI3n+1 (FA = formamidinium, MA = methylammonium) films show a significantly improved film quality with enlarged grain sizes and vertical orientation to the substrate. Moreover, perovskite films prepared from the HTI embedded PbI2 layer also exhibit greatly reduced film decomposition from oxygen and humidity in ambient air conditions. As a result, the champion device shows a high power conversion efficiency (PCE) of 13.06%, in contrast to 7.98% for the 3D (FA)x(MA)1–xPbI3 perovskite device without HTI dication. The 2D DJ (HTI) (FA)x(MA)1–xPbnI3n+1 devices show enhanced stability, maintaining 72% of their initial PCE after 2000 h in ambient air conditions (relative humidity 35–50%). However, the 3D (FA)x(MA)1–xPbI3 perovskite device dropped to 24% of its PCE within 2000 h. Our results suggest that the precursor engineering containing 2D perovskite organic spacer in a two-step process is a potential approach toward further improving the PCE and stability of the 2D DJ perovskite solar cell.