Research On Synthesis And Photoelectric Performance Of Sensitizers With Novel Donor

Dye-sensitized solar cells and photocatalytic for hydrogen evolution are considered to be the two effective strategies for utilizing sunlight.In these two processes,the sensitizer is the key component for harvesting sunlight and transferring electrons.Metal-free organic photosensitizers have attracted great attention owing to their chemical versatility and facile synthetic approaches high molar extinction coefficients and broaden solar spectral absorption when compared with the metal complex sensitizer.It is usually composed of electron donor(D),conjugated bridge(?),electron acceptor(A)and anchor group.The donor moiety is generally away from the semiconductor and contact with electrolyte(sacrificial agent)for promoting the regeneration of the dye molecule.The coupling of the acceptor to the semiconductor facilitates the electron injection into the semiconductor.In this thesis,many efforts have been devoted to the the modification and extension of electron donor and systematical investigation of relationship between the structure of the electron donor and the device performance.Besides,the molecular structure were further optimized,and the relationship between the structure of the dye molecules,the mode of action with semiconductor,and the photo-catalytic properties were studied in detail.Based on this push-pull electronic structure,attempts have been made to combine the D-A structure with room temperature phosphorescence and mechanoluminescence to explore the intrinsic relationship between molecular structure-packing mode-function.The main research contents are as follows:In chapter 1,the introduction section briefly introduces the development history,operational principle,evaluation parameters and their influence factors of dye-sensitized solar cells(DSCs)and photocatalytic for hydrogen evolution and highlighted the dyes with D-?-A structure and their application in DSCs,photocatalytic hydrogen evolution,room temperature phosphorescence(RTP)and mechanoluminescence(ML).Then the design ideas and research are put forward.In chapter 2,tetraaryl-1,4-dihydropyrrolo-[3,2-b]pyrroles(TAPP)with spatial stereostructure and electronic properties was developed as an novel electron donor and four dyes(LI-127-130)were designed and synthesized by modifying the donor moiety and adjusting the conjugate bridge.Equipping with thiophene as conjugated bridge is beneficial for broadening the absorption spectral to increase the photocurrent.The modification of novel donor with triphenylethylene with large size and twisted structure is beneficial for inhibiting dye aggregation and electron recombination.Under the balance of photocurrent and open-voltage,LI-130 exhibits the best conversion efficiency of 6.56%(J_sc=13.78 m A cm^-2,V_oc=664 m V,FF=0.72)and could be improved to 2 times in dim light irradiation.In chapter 3,based on the TAPP unit,a novel electron donor(indolo[3,2-b]indole)with a planar fused ring structure was introduced.Four organic dyes(LI-133-136)incorporated with different electronic properties and spatial structures were designed and synthesized.The planar fused ring structure facilitates the electron transport and could stabilize the excited state electrons.The introduction of the auxiliary donor unit can not only adjust the electronic properties,but also optimize the spatial configuration of the donor unit.The sensitizer LI-133 combining planar fused ring structure(Indolo[3,2-b]indole)with the three-dimensional spatial structure(triphenylamine unit)show the highest conversion efficiency of 8.34%(J_sc=16.75 m A cm^-2,V_oc=705 m V,FF=0.71).At the same time,these four dyes were also applied to the photocatalytic hydrogen evolution.The hydrogen production of the LI-133 was 1263?mol in 8 hours.In chapter 4,two organic dyes(LI-131 and LI-132)with D-A-?-A structure incorporated with benzothiadiazole for broadening absorption spectra and benzene or thiophene as spacer groups were designed and synthesized.Combined with LI-127-130,the relationship between molecular structure and photocatalytic for hydrogen production performance was systematically studied.LI-131 with a wide spectral response and ability to prevent electron recombination and electron back transfer exhibits the best hydrogen production performance of 1301?mol in 5 hours.Combined with the hydrogen production performance and the DSCs performance of 6 sensitizers,it can be calculated that the requirements of molecular design for photocatalytic for hydrogen production and DSCs are different,providing a reference for the subsequent suitable molecular design in different energy fields.In chapter 5,the effects of two different action modes on photocatalytic performance were studied by adjusting the action modes of dye molecules and semiconductors.The interaction between the molecule and the semiconductor is strong and electron injection as well as electron back transfer are fast when the carboxyl group bonded to a semiconductor surface by a covalent bond.However,the formation of a heterojunction between the molecular and semiconductor could slow down the electron injection rate and electron back transfer.What's more,the combination of bonding and heterojunction shows that the photocatalytic performance has been further improved.This was due to the formation of the heterojunction that inactivated the defects of the semiconductor and reduce the electron recombination,resulting in the improved stability and performance.The above results indicate that the combination of bonding and heterojunction between the dye and the semiconductor is an effective method for improving photocatalytic activity and stability.In chapter 6,three ester groups with lone pair electrons were incorporated with TPA on ortho-position,and TPA-o-3COOMe was designed and synthesized.Not only RTP and ML properties have been successfully integrated in the same molecular but also the two different properties were successfully distinguished by two different crystalline polymorphs.The P-1 crystal accompanied with visible room temperature phosphorescence(RTP)and Pn crystal is mechanoluminescence(ML)active.Careful analyses of these crystal structures make it clear that the different functions are highly related to totally different molecular packing modes.A homogeneous molecular packing with strong intermolecular interaction,is conducive to the RTP function,while,the crystal which is inhomogeneous packing and disorderly arrangement,is easily broken at the weakness upon mechanical stimulus,which is beneficial for the ML function.For further comparison,the three ester groups were combined with TPA in the meta or para positions,respectively,and TPA-m-3COOMe and TPA-p-3COOMe were obtained.It was found that the local uniform layered arrangement could facilitate non-radiation for the impossible RTP and ML.