Introducing S,F Into Spiro [Fluorene-9,9’-Xanthene](SFX) Based Hole Transport Materials For Sensitive-dopant-free Perovskite Solar Cells

In recent years,organic-inorganic hybrid perovskite solar cells have become a research hotspot of new generation solar cells,which contributed to their abundant material sources,simple production processes,high efficiency,et al.,due to their excellent performance.Perovskite solar cells（PSCs）are composed of working electrodes（SnO₂:F）,electronic transport layer,perovskite light harvest layer,hole transport layer and metal electrodes（Au,Ag,etc.）.Hole transport materials（HTMs）,which can extract and transport holes,inhibit charge recombination and generally prevent perovskite from exposure to water,have become an indispensable part in perovskite solar cells.Therefore,developing HTMs with suitable energy level,high hole mobility and good hydrophobicity has become one of the research hotspots.In this thesis,considering four empirical criteria that an ideal sensitive-dopant-free HTMs should satisfy,a series of spiro[fluorene-9,9’-xanthene]（SFX）based HTMs containing S,F heteroatoms were designed and synthesized.After characterizing the photophysical properties,hole transport properties and hydrophobicity of the synthesized compounds,their applications in PSCs devices were explored.The results are obtained as follows:1.Two compounds SFX-DTF1 and SFX-DTF2,which were SFX-centered and DTF derivative 4,5-bis（methylthio）-1,3-dithiole-2-thione（MDT）as the peripheral substituent group,but differing in different substituent positions in the SFX core were synthesized.The results show that the DTF functionalized compounds SFX-DTF1 and SFX-DTF2 have suitable HOMO levels,good hole mobility and hydrophobicity.SFX-DTF1 has a higher hole mobility of 1.51×10^-4 cm² V^-1 S^-1,which is beneficial to collect and transport holes.The water contact angle of SFX-DTF1 was 93°,which can effectively prevent water from eroding the perovskite surface.As a result,the PSCs based on the sensitive-dopant-free SFX-DTF1 and SFX-DTF2 yields a moderate PCE of 10.67%and 8.78%,respectively.The stability test results show that SFX-DTF1 and SFX-DTF2based devices have better stability than that of Spiro-OMeTAD based devices.2.In order to further improve the efficiency of PSCs,compounds 2pF-X59and 2m F-X59 were synthesized by two-step reaction with fluorinated SFX as core and 4,4’-dimethoxydiphenylamine as peripheral substituent group.The results showed that 2pF-X59 and 2m F-X59 had lower synthesis cost and higher hydrophobicity than Spiro-OMeTAD.In comparison with nonfluorinated compound X59,2pF-X59 and 2m F-X59 show lowered HOMO level,improved hole mobility and hydrophobicity.As a result,14.41%and 15.45%PCE were obtained from the original 2pF-X59 and 2m F-X59 based PSCs device,respectively.We chose 2m F-X59 devices with better performance for further optimization.Aided by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane（F4TCNQ）to further lower the HOMO level of 2m F-X59 and improve the morphology of the film.The efficiency of optimized 2m F-X59 based PSCs were increased to 18.13%.The stability test results show that the sensitive-dopant-free2m F-X59 based PSCs maintaining 95%of their initial performance for more than500 h under air exposure,showing much better long-term stability.