3,6-Bis(methylthio)-9H-carbazole Based Self-Assembled Monolayer for Highly Efficient and Stable Inverted Perovskite Solar Cells.

The photovoltaic performance of inverted perovskite solar cells (PSCs) relies on effectively managing the interface between the hole extraction layer and the light-absorbing perovskite layer. In this study, we have synthesised (4-(3,6-bis(methylthio)-9H-carbazol-9-yl)butyl)phosphonic acid (MeS-4PACz), which forms a self-assembled monolayer (SAM) on the fluorine-doped tin oxide (FTO) electrode. The molecule's methylthio substituents generate a favourable interfacial dipole moment and interact with the perovskite layer. This interaction results in well-aligned energy levels among the FTO/SAM/perovskite layers, promoting efficient hole extraction and significantly reducing carrier recombination losses. Additionally, the methylthio groups passivate iodide vacancies and interact with Pb ions of the perovskite, reducing defect-induced trap states and enhancing the crystalline growth of the perovskite layer. Consequently, inverted PSCs incorporating MeS-4PACz achieve a power conversion efficiency of 25.13 %, along with outstanding photostability.