Research On The Characteristics Of Light Absorption And Charge Transfer In Organic Photoactive Layer

With the rapid development of community economy and sharp growth of population,the demand for energy is increasing day by day.At present,the energy demand of human society mainly comes from fossil fuels such as coal,oil and natural gas.Because of the limited reserves of fossil fuels and the pollution to the earth's environment,people began to search for and develop new renewable energy sources.In renewable energy such as tidal and wind power,solar energy has been highly praised by researchers because of its advantages such as unlimited reserves,no pollution and easy popularization.The use of organic solar cells to convert light energy into electrical energy is one of the effective ways to utilize solar energy.Organic photoactive layer is one of the core parts of organic solar cells,and its performance determines the level of photoelectric conversion efficiency of organic solar cells.In this paper,we study the characteristics of light absorption and charge transfer properties of organic photoactive layer,which can be divided into two parts.In the first part,the effect of sulfur atom substitution on the ground state properties,absorption spectra and charge transport properties of benzodifurandione-based PPV(BDPPV)was investigated by using density functional theory(DFT)and time-dependent DFT(TD-DFT).The ground state structure,frontier molecular orbital,electron density distribution,ionization energy,electron affinity,absorption spectrum,electron/hole recombination energy and mobility of BDPPV and its derivatives were calculated.By comparing the calculated results,we analyzed the difference of the optical properties of BDPPV and its derivatives,which provided valuable reference information for further molecular design.Considering the practical application,the influence of external electric field on the orbital energy levels and absorption spectra of BDPPV and its derivatives were studied.The calculated results showed that the sulfur atom had the siginificant effects on the bond lengths,dihedral angles and absorption spectrum of BDPPV;with the increase of conjugated degree,the HOMO energy levels of BDPPV and its derivatives increased,the LUMO energy levels decreased,energy gaps decreased,the ionization energies decreased,the electron affinities increased,and the absorption spectra were red shifted.The ground and excited state properties of the four atoms substituted by sulfur atoms are better than those of the other molecules in the designed molecules,which indicated that the molecules replaced by the four sulfur atoms can be selected as the candidates of the photoactive layer materials.In the second part,the physical and electrical properties of the dyes purpurin and alizarin complexone were investigated experimentally and theoretically for the dye-sensitized solar cells(DSSCs)application.The UV-Vis absorption spectra,cyclic voltammetry curves,current-voltage characteristic curves and electrochemical impedance properties of the two dyes were tested.As compared with the experimental results,the frontier molecular orbitals,static first hyperpolarizabilities,absorption spectra,driving forces of electron injection and dye regeneration of the dyes were calculated by using density functional theory(DFT)and timedependent DFT(TD-DFT)methods.The results showed that the introduction of side chain made alizarin complexone have the better performance than that of purpurin,and alizarin complexone exhibited higher short circuit current density due to the higher driving forces of electron injection and dye regeneration.