Indolo[3,2-b]indole-based crystalline hole-transporting material for highly efficient perovskite solar cells

We have designed and synthesized fluorinated indolo[3,2-b] indole (IDID) derivatives as crystalline holetransporting materials (HTM) for perovskite solar cells. The fluorinated IDID backbone enables a tight molecular arrangement stacked by strong pi-pi interactions, leading to a higher hole mobility than that of the current HTM standard, p, p-spiro-OMeTAD, with a spherical shape and amorphous morphology. Moreover, the photoluminescence quenching in a perovskite/HTM film is more effective at the interface of the perovskite with IDIDF as compared to that of p, p-spiro-OMeTAD. As a consequence, the device fabricated using IDIDF shows superior photovoltaic properties compared to that using p, p-spiroOMeTAD, exhibiting an optimal performance of 19%. Thus, this remarkable result demonstrates IDID core-based materials as a new class of HTMs for highly efficient perovskite solar cells.