Controlling The Light-harvesting Ability Of Dithiafulvene Derivatices: Synthesis And Application In Solar Cells

Donor-acceptor（D-A）type of organic dyes have shown great applications due to their intramolecular charger transfer（ICT）effect.Combining with their low cost,high molar extinction coefficient and feasible molecular structure tailoring,the D-A type organic dyes have been widely used in the field of dye-sensitized solar cells,organic small-molecule / polymer solar cells and so on.In the dye-sensitized and organic small-molecule / polymer solar cells,the D-A type organic dyes play an important role in the harvesting of sunlight,which directly influences the power conversion efficiency of the cell,indicating the study of D-A dyes is of great significance to improve the solar cells performance.In this thesis,we aim to improve the light-harvesting ability of D-A type dithiafulvene derivatives via electron acceptor and conjugate bridge unit modification.Finally,their applications in dye-sensitized solar cells and organic small-molecule solar cells have been explored.The results are obtained as follows:1.Two monomer type dithiafulvene based organic dyes DTFPy3 and DTFPy4 both with a pyridine acceptor but differing in the phenyl-thienyl and thienyl-phenyl π-bridges,and two correspondent dimeric congeners D-DTFPy3 and D-DTFPy4 have been synthesized.The experimental results showed that the arrangement of the electron-rich thienyl group adjacent to the electron donor moiety in the π-bridge red-shifted the absorption,the dimeric type molecules can significantly improve the absorption intensity of the organic dyes,which is about two times than that of the monomer type molecules.Among them,D-DTFPy4 garnered the highest light harvesting efficiency,and the D-DTFPy4 based dye-sensitized solar cell can yield an overall power conversion efficiency up to 5.26%.2.In order to improve the capability of the dithiafulvene dyes to efficiently collect light in the whole visible region,the DTCF with dithiafulvenyl donor and TCF acceptor,linked by “phenyl-3,4-ethoxylene dioxy thiophenyl（EDOT）-phenyl” π-conjugated bridge was designed and synthesized.The experimental results showed that DTCF has two absorption bands boath located in visible region.For example,in tetrahydrofuran solution,one peaking at 548 nm and the other peaking at 401 nm,their their molar extinction coefficient was4.65×104 M^-1 cm^-1and 3.79×104 M^-1 cm^-1,respectively.It was found the absorption spectrum uniformly covers the whole visible region from 400 nm to700 nm.The organic solar cell based on DTCF as donor and PC61 BM as acceptor,yielding a power conversion efficiency of 0.28%.3.To further uplift the absorption intensity of dithiafulvene dyes in whole visible region,D-DTCF,the dimerization of DTCF,was synthesized and studied.The experimental results showed that compared with the monomer DTCF,the dimer D-DTCF can greatly improve the absorption intensity.The absorption peaks in tetrahydrofuran solution are located at 532 nm and 401 nm,respectively.However,their molar extinction coefficient reached 5.76×104 M^-1cm^-1 and 4.40×104 M^-1 cm^-1,respectively,which are 1.2-fold and 1.1-fold higher than their corresponding monomer ones.The remarkable capability of D-DTCF to collect light in visible region indicates its potential for high efficient solar cells.