Transport Properties Of Thiophene And Its Derivatives As Hole Transport Materials

With the increasing scarcity of fossil resources and the explosion of people's demand for energy,people are searching for clean,renewable and pollution-free energy.Solar energy stands out among many alternative energy sources.Among the many solar cell types,perovskite solar cells(PSCs)have higher photoelectric conversion efficiency compared with other organic solar cells.It with advantage of high performance,cheap produce and easy manufacture attracts more attention.The work of this paper is divided into two parts.In the first part,density functional(DFT)and time-dependent density functional(TD-DFT)were used to optimize the ground state structure of the original molecules(HTM1,HTM2)of two trianiline classes and four designed molecules(HTM3,HTM4,HTM5,HTM6),and B3LYP functional optimization was performed on the 6-31G(d)basis group.Based on the ground state optimization data,the bond length,the bond angle,energy levels,energy gap,ionization energy and electron affinity(IPs EAs)of six molecules were calculated and the frontier molecular orbital of the experimental and design molecules were drawn.Based on the ground state optimization structure,the time-density functional(TD-DFT)method was used to calculate the absorption spectrum.On the basis of the excitation state optimization,the time-density functional(TD-DFT)method was used to calculate the fluorescence spectrum.The anions and cations of the experimental and design molecules were optimized by using Marcus theory to calculate the recombination energy and hole mobility.The relevant parameters of the photoelectric properties of HTM1-6 were theoretically studied.The results showed that the atomic substitution had little influence on the bond length,bond angle and the stability of the molecule.At the same time,it was found that the introduction of silicon atoms significantly increased the HOMO level and hole injection force,and the hole transfer integral of molecules significantly increased,leading to the increase in the hole mobility of molecules.The introduction of silicon atoms led to better IP,EA and smaller energy gap,which was conducive to charge transfer and redshift spectrum.The introduction of silicon atoms has a great influence on the hole mobility and hole migration rate.Compared with experimental molecules and other designed molecules,the hole mobility was greatly improved.Molecular substitution can improve the photoelectric properties of molecules and provide a possible choice for the design and synthesis of hole transport materials for perovskite solar cells.In the second part,the ground state structure of 5 experimental molecules(M1-5)and 2 design molecules(Ml-2)was optimized by DFT method in dichloromethane solvent and B3LYP function of 6-31G(d)basis group.These seven molecules have the same triphenylamine structure and different substituents.The HOMO of M105 molecule is the lowest,and the HOMO of design molecule MS1 is close to M105,with a difference of 0.019 eV.The smaller the energy difference between the HOMO and the perovskite valence band,the higher the open circuit voltage may be for MS1 molecules.In terms of solubility,MS1 also shows excellent performance in effectively reducing production investment.Most importantly,it has the maximum hole mobility of MS 1 than that of the optimal experimental molecule M104.We can use molecular simulation to explain the differences of experimental molecular properties;by means of assistant molecular design and changing the molecular structure,high-performance materials will be selected,which provides an effective way for the synthesis of experiments.