A Dispiro-Type Fluorene-Indenofluorene-Centered Hole Transporting Material for Efficient Planar Perovskite Solar Cells

A novel dispiro[fluorene-indenofluorene]-based compound, dispiro-OBuTAD (shortened as Dispiro) with a 3-2 spiro core is designed and synthesized as a hole transporting material (HTM) for perovskite solar cells (PSCs). The Dispiro with two spiro centers shows rigid ladder-type structure, great steric hindrance, and reduced molecular symmetry, which favor good thermal stability and homogeneous film morphology. Devices with Dispiro as HTM afford a high power conversion efficiency amounting to 18.46% in MAPbI(3)-based planar PSCs, which is higher than the value (17.82%) of the well-known spiro-OMeTAD-based devices. The Dispiro can form amorphous homogeneous films with improved hole mobility and enhanced hole extraction from perovskite to HTM, resulting in high performance of Dispiro-based PSCs. This work provides the first example of fluorene-indenofluorene-centered dispiro-type HTM for PSC application, suggesting a promising approach to design HTMs by increasing the spiro center.