Abstract: The recent advances in perovskite solar cells (PSCs) surprised the traditional photovoltaic community. The power conversion efficiencies (PCEs) of PSCs have achieved more than 20%, in which the key functional layer is currently constituted by spirobifluorene (SBF)-based hole transporting materials (HTMs), typically known as spiro-OMeTAD. In the meanwhile, a new rising spiro-core, spiro[fluorene-9,9′-xanthene] (SFX), has attracted great interest for contrasting HTMs. SFX exhibits two main advantages compared with SBF: one is low-cost, the other is high stability. Hence, a lot of highly efficient HTMs based on SFX have been designed and synthesized, and the corresponding PSCs devices have shown competitive performances with spiro-OMeTAD- based cells. In this minireview, we summarize the structure-performance relationship of high-efficiency SFX-based HTMs for PSCs. The effects of the highest occupied molecular orbital (HOMO) energy level, hole mobility and conductivity, film-forming ability of SFX-based HTMs on the PCEs have been focused.

Key words: spiro[fluorene-9,9′-xanthene], perovskite solar cells, hole transport materials, power conversion efficiency, spiro-OMeTAD