Blending isomers of fluorine-substituted sulfonyldibenzene as hole transport materials to achieve high efficiency beyond 21% in perovskite solar cells

In this article, two fluorine-substituted sulfonyldibenzene compounds are synthesized and characterized (denoted as 3, 6-SFY and 2, 7-SFY), and they are mixed as hole transport material (HTM) in conventional perovskite solar cells (PSCs). 3, 6-SFY and 2, 7-SFY show good compatibility when they are blended due to their highly similar conjugated structures. The mixed HTM film exhibits suitable energy level and uniform surface morphology. Moreover, improved hole mobility and hole extraction ability was detected in the mixed isomersbased HTM compared to the single-component HTM. As a result, conventional perovskite solar cells using the mixed isomers as HTM deliver a maximum power conversion efficiency of 21.41%, significantly higher than that obtained in 3,6-SFY (19.02%) and 2,7-SFY-based devices (20.29%). These results demonstrate that mixing two isomers as HTM is a promising way to improve device performance. As far as we know, this is the first example of blending two isomers in conventional PSCs, and the results in this work also provide a new sight in developing highly efficient hole transport materials.