New dithieno[3,2-b:2',3'-d]pyrrole-based organic precursors of holetransporting self-assembled monolayers for highly efficient Perovskite Solar Cells

Thanks to the very high efficiencies in the sunlight-to-electricity conversion gained in the last ten years, Perovskite Solar Cells (PSCs) attracted tremendous interest, stating as one of the leading technologies in the next-generation photovoltaic field. To increase stability and performance, several alternatives to the original device architecture and the materials composing the PSC layers have been investigated. About the hole-transporting layer (HTL), a breakthrough has been represented by the introduction of small organic molecules capable of forming a very thin self-assembled monolayer (SAM) onto the ITO electrode and extracting the photogenerated hole from the perovskite layer. The main advantages of using SAMs in comparison to traditional hole-transporting materials (HTMs) are their cost-effectiveness and their stability, as well as the pointlessness additives. In this work, we investigated the properties of a new family of six organic precursors of SAMs (MS36-45-47 and QM06-08-10) based on the tricyclic structure of the dithieno[3,2-b:2',3'-d]pyrrole and bearing a phosphonic acid as the anchoring group to the ITO electrode. Different aryl substituents in 2- and 6-positions have been introduced to modulate the photo-electrochemical properties of the final SAMs, while a common and straightforward synthetic procedure has been optimized for all the compounds. A preliminary screening of test PSCs containing the new compounds outlined QM06 and QM10 as the best-performing SAM precursors, outperforming the PCE values of the standard literature reference 2-MeOPACz. Optimization of the PSC construction and full characterization of the devices is ongoing.