“…Perovskite solar cells (PSCs) are emerging as a hot spot in the photovoltaic field due to numerous merits such as low production cost, ease of device fabrication, excellent photoelectric properties, etc. − In the past decade, PSCs have made a major breakthrough in photovoltaic performance with the certificated power conversion efficiency (PCE), which rapidly grew from 3.8% to 25.7%. − The charge transport layers, playing the role of charge extraction/transport and suppressing nonradiative recombination, are critical for highly efficient PSCs. ,− To date, 2,2′,7,7′-tetrakis[ N , N -bis( p -methoxyphenyl) amino]-9,9′-spirobifluorene (spiro-OMeTAD) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) are the most commonly used hole transport materials (HTMs). − Although they achieved satisfactory efficiencies, the complex synthetic route and purification process of spiro-OMeTAD and PTAA make the device cost a bottleneck for large-scale applications. Numerous researches have focused on developing novel, low-cost, and highly efficient HTMs, and increasing molecular dipoles, regulating molecular energy levels, and imitating the three-dimensional structure of spiro-OMeTAD are proved to be effective design strategies to develop efficient HTMs. ,− The spiro structure will bring a steric cross configuration to enhance the charge transport between molecules and, at the same time, improve the solubility of the material and film formation property. Among several spiro-type HTMs, spiro-[fluorene-9,90-xanthene] (SFX) core-based molecules possess facile synthesis steps and excellent optoelectronic properties, rendering SFX a promising core structure for the development of charge transport materials, especially HTMs. , Xu and Bi et al applied SFX-based HTMs X60 and X59 in PSCs, respectively, and achieved comparable PCEs (19.84% and 20.8%) to a well-known spiro-OMeTAD device.…”