Perylene Diimide-Based Dimeric Electron Acceptors with Molecular Conformations for Perovskite Solar Cells

This paper reports five novel PDI dimer type electron transport materials (ETMs) employing o-indoloquinoxaline (o-Iq), m-indoloquinoxaline (m-Iq), and cibalackrot (Ci) groups as the core building blocks and presents the twisted structures of PDI dimers coded as PDI-NHR-o-Iq, PDI-o-Iq, PDI-NHR-m-Iq, PDI-m-Iq and PDI-NHR-Ci dyes (see Scheme 1 and 2). We have systematically compared their photophysical, electrochemical, and optoelectronic properties with respect to the reference dye (2PDI-NHR), which is directly connected of two PDI planes. Their calculated HOMO-LUMO energy levels are sufficient for charge transfer to the perovskite material so that structure-photovoltaic performance relationship of synthesized ETM dyes can be evaluated. When the binding position of indoloquinoxaline group between PDI rings are changed from o- to m- positions, most of the photophysical and electrochemical properties of PDI dimer are dramatically changed, finally improving the photovoltaic performances. Indoloquinoxaline and cibalackrot subunits covalently attached to perylene diimide dimers decorated with long-alkyl chains used as ETM are coated on the MAPbI2Br perovskite surface to manufacture solar cells. Attaching groups improve the charge transfer capability of the material depending on their molecular conformation, which plays important role in adjusting the energy level between the perovskite material and the ETL. image