A hole-transporting material with substituted fluorene as end groups for high-performance perovskite solar cells

High-performance hole-transporting materials (HTMs) play an essential role in improving efficiency and stability of perovskite solar cells (PSCs). Herein, we developed a new sulfonyldibenzene core based HTM named CS-06, which contains substituted fluorene-terminated moieties as end groups in molecular structure. It is found that, the substituted fluorene-terminated end groups render CS-06 with a deep HOMO level, high hole mobility and glass transition temperature, which are beneficial for improving hole extraction and decreasing recombination probabilities at HTM/perovskite interface. The champion device based on CS-06 can yield a power conversion efficiency of 21.10%, superior to devices based on its analog CS-04 (19.73%) as reference. This work provides an effective way to develop efficient HTMs through rational end group design to boost the photovoltaic performance of PSCs.