Synthesis And Properties Of Star-shaped Small Photovoltaic Materials Based On Triphenylamine And Benzothiadiazole Derivatives

This dissertation introduced the linear and star-shaped small molecules as electrondonating materials,and their research status of organic solar cells(OSCs)systematically.Currently,the relationship between molecule stucture and photovoltaic property of organic small molecules as electron-donating materials is not clear,and the power conversion efficiency(PCE)of OSCs has not reached the practical level.In order to obtain organic small molecules as electron-donating materials possessing broad absorption,matched energy levels with electron-accepting materials,and high mobilities,and to further reveal the relationship between molecular structure and photovoltaic property of electron-donating materials and obtain OSCs with the high efficiency,this paper carried out the molecular design,synthesis and their property study of the star-shaped organic small molecules used as photovoltaic donor materials,which contain a central electron-rich donor(D)unit of triphenylamine(TPA)or tris(2-methoxyphenyl)amine(TPA-OMe)unit,three armed electron-deficient acceptor(A)units of benzothiadiazole(BT)and BT derivatives,and three terminal polycyclic aromatic(Ar)units of carbazole(Cz).Their molecular structure were characterized by1 H NMR,13 C NMR,time-of-flight mass spectra(TOF-MS)and elemental analysis.Moreover,the effect on thermal stability,photophysical,electrochemical,electron cloud density distribution and photovoltaic properties was systematically studied by using thermogravimetic analysis(TGA),ultraviolet absorption spectrum,cyclic voltammetry(CV),density functional theory(DFT)calculations and device performance test.The research findings are mainly stated as follows:1.A type of star-shaped organic small molecules used as electron-donating materials of TPA(Fx BT-T-3Cz)3(x = 0,1,2)was designed and synthesized,which contain a central electron-rich D unit of TPA,three armed electron-deficient A units of BT and its derivatives(F1BT and F2BT),and three terminal Ar units of Cz.The research results indicate that introducing F atom into BT unit has decreased the highest occupied molecule orbital(HOMO)effectively,and enhanced the open-circuit voltage(Voc)and short-circuit current density(Jsc)values for their OSCs.The highest Voc of1.01 V and Jsc of 10.84 m A cm-2 were obtained in the TPA(F2BT-T-3Cz)3-based solar devices with a comparable PCE of 4.81%,respectively.2.Another type of star-shaped organic small molecules used as electron-donating materials of TPA-OMe(Fx BT-T-3Cz)3(x = 0,1,2)were designed and synthesized,which contain a core of TPA-OMe unit,three armed units of BT or its derivatives(F1BT and F2BT),and three terminal units of Cz.The influence of methoxyl(-OMe)and F atom on device performance was studied for their OSCs.The results indicate that TPA-OMe(Fx BT-T-3Cz)3 exhibit better solubility and higher hole mobility in comparison with TPA(Fx BT-T-3Cz)3.It is found that their solubility was improved by introducing-OMe unit and HOMO energy level was gradually decreased with an increase of F substitution for TPA-OMe(Fx BT-T-3Cz)3.However,the light absorption efficiency and the PCE value were unexpectedly reduced by introducing-OMe unit in TPA-OMe(Fx BT-T-3Cz)3.Among the TPA-OMe(Fx BT-T-3Cz)3(x = 0,1,2)the TPAOMe(F2BT-T-3Cz)3 revealed the best photovoltaic performance with a Voc of 0.96 V,a Jsc of 7.44 m A cm-2,and a PCE of 4.50% owing to the increase of F atom sustitution.3.This work has revealed the effect relationship of molecular structure on thermal stability,photophysical and electrochemical properties,as well as electron cloud density distribution and photovoltaic properties,where the organic small molecules used as electron-donating materials contain a central TPA or TPA-OMe units.It is important significance to promote the development and application of organic small molecules used as materials.