Synthesis,Properties And Application Of Triphenylamine-based Hole Transport Materials Containing Thiophene Unit

In recent years,organometal halide perovskite-based solar cells have emerged at the forefront of solar cells and attracted increasing interests because of their high efficiency,low cost and easy fabrication.The power conversion efficiencies of perovskite solar cells have been increasing rapidly from 3.8% up to 20%.At present,Spiro-OMeTAD,which is commonly used hole transport materials in perovskite solar cells,bears the disadvantages of complex synthetic route,high cost and so on.So,it is very important to design and develop new efficient and low cost hole transport materials.In this dissertation,five hole transport materials D1,D2,D3,S1 and S2 were designed and synthesized,which were based on alkoxythiophene core and triphenylamine units linked with carbon-carbon single bonds or double bonds or connected through a central carbon atom.All compounds were characterized by nuclear magnetic resonance(NMR)and mass spectrum(MS)technologies.Quantum chemical calculations indicate that the HOMOs of molecules spread over the whole molecule,which is favorable for hole transport.Similar to Spiro-OMeTAD,compounds S1 and S2 with spiro linkage are consist of two identical orthogonal ?-conjugated moieties.The introduction of a spiro linkage into low molecular weight organic compounds won't influence the energy levels of original molecular half.The tests of UV-vis absorption spectra,fluorescence emission spectra and fluorescence quantum efficiency show that the introduction of a spiro linkage doesn't change photophysical properties of original molecular half,while the introduction of double bonds will reduce the band gap and cause a red shift of spectrum.The thermal properties of the materials were studied by TGA and DSC.All compounds possess high decomposition temperature of 377 ~ 431 ?.The glass transition temperature of the compound S1 and S2 are 158 and 153 ?,which are significantly increased because of spiro structure.The energy levels of compounds were obtained by cyclic voltammetry combined with UV-vis absorption spectroscopy data.HOMO energy levels of the compounds are between-5.32 e V and-5.17 eV,which are suitable to be used as hole transport layer for perovskite solar cell.The solubility test showed that the target compounds have good solubility,but the introduction of spiro structure will reduce the solubility of the molecules.All hole transport materials showed good film forming property.The organic thin films of D1,D2,D3,S1 and S2 fabricated by spin-coating showed stable amorphous state,which could be supported by the X-ray diffraction.The thin films also had uniform morphology surface properties,exhibiting smooth surfaces with a root mean square roughness in 1 nm,which could be supported by atomic force microscopy images.The devices of FTO/TiO2/CH3NH3PbI3/HTMs(dopant-free)/Au based on D1,D2,D3,S1 and S2 exhibited encouraging power conversion efficiency of 7.12%,4.51%,8.02%,5.27% and 5.97%,respectively.Devices based on p-doping(LiTFSI/TBP)of D3 and S2 obtained efficiency of 12.39% and 12.56%,respectively.