Impact of fluorine substitution in organic functional materials for perovskite solar cell

In photovoltaic technologies, perovskite solar cells (PSCs) have gained significant consideration due to their attractive properties such as high absorption coefficient, long charge carrier diffusion length, easy solution processability, and growth into one of the important classes of low-cost and easily scalable photovoltaic devices. Moreover, to further enhance the photovoltaic performance and make stable PSCs, fluorine substituted organic materials are widely employed. The first main reason is that fluorinated organic materials have higher hydrophobicity, which can effectively enhance the humidity stability of PSCs. The other reason is that fluorine substitution in organic materials is reported to be an effective way to regulate the energy level alignment, optimize perovskite film morphology, passivate the surface and boundary defects, and enhance the device performance. This review endeavours to illustrate the fluorine substitution in organic cation of perovskite precursors and their interfacial engineering through fluorinated dopants/additives. Moreover, the review covers the effect of fluorine substitution in the hole transporting layers (HTLs), electron transporting layers (ETLs), and fluorinated organic small molecules as dopant/additives into HTLs and their chemical interactions between the perovskite layer. We discussed the relationship between chemical structures, photophysical, electrochemical properties, and their photovoltaic performance in each part.