The Effect of Sequential Spin-Coating Perovskite Deposition on the Self-Assembled Monolayer of Inverted Perovskite Solar Cells

Organic-inorganic halide-based perovskite solar cells (PSCs) are gaining attraction in the energy technology field due to their rapid development. Nevertheless, addressing issues such as cost reduction or maximizing performance and stability by improvements of fabrication processes and materials is necessary for commercialization. Therefore, researchers have been focusing on improving the performance and stability of the inverted structure of PSCs, suitable for low-temperature processes and tandem solar cells, particularly by using self-assembled monolayers (SAMs) as the hole transport layer (HTL). In the meantime, the fabrication process suitable for roll-to-roll processing is necessary for large-area production. A sequential spin-coating process depositing the PbI₂ first, followed by the deposition of organic halide to form a perovskite film is suitable for roll-to-roll processing since it does not require additional anti-solvent treatment or vacuum flashing process. However, the sequential spin-coating deposition process has the disadvantage that a polar solvent is applied continuously, which can affect the underlying SAMs-based HTL. Previous studies have shown that strong polar solvents can cause desorption of SAMs due to the easy detachment of anchoring between the SAMs and substrate. In addition, detached molecules by strong polar solvents can randomly redeposit in the bottom layer during perovskite crystallization, blocking carriers to the bottom electrode. Therefore, the more detached molecules are desorbed from the surface, the higher the leakage current and the lower the power conversion efficiency (PCE). As a result, the sequential spin-coating deposition process on SAMs can be very unfavorable. In this study, we aimed to investigate the compositional changes at the interface of HTL and perovskite films using a sequential spin-coating deposition process and to identify the differences between sequential spin-coating deposition and one-step spin-coating processes. Finally, we can propose a solution to improve the application of SAMs to perovskite fabricated by sequential spin-coating.