First Principle Study Of Polythiophene And Its Derivatives

Organic solar cells are hotspot in current research. The heterojunction structureis widely accepted. Commonly, in this structure, polythiophene and its derivatives(P3HT) are mainly donor materials. And fullerene and its derivatives (PCBM) arereceptor. This paper is about the study of donor photoelectric performance primarimly.We can do chemical modification by introducing the substituent to improve organicpolymers. Here, polythiophene is matrix material. And then, we introduce thesubstituent of methyl and benzothiazolyl to increase its conductivity.(1) We calculate the band structure,state density distribution andoptical dielectricconstants of polythiophene by VASP software.The results get that its band gap isbetween insulator and semiconductor.In the brillouin zone edge,the band structure istwo connection each other.Compared with other polymers, this is its own conductiveadvantages which can be used as the material of organic cells. However, due to itsstructure features, the electrical conductivity is not very good.So we hope to improveits conductivity by the methods of chemical doping.This means can reduce the bandgap of the polymer.(2) There is a lot of substituent can be doped. We choose firstly alkyl-methyl toreplace. But, change of conductivity is not big with the increase of long chainsubstituents. So we choose the smaller methyl to replace. Through calculation.Weconclud that plane structure of methyl-thiophene has the smallest band gap.That isslightly smaller than polythiophene. It has its advantages on the optical properties.The value of conductivity not only has a peak in the X axis direction, also largeroccupies in the Y direction. That is more ideal than intrinsic polythiophene on Xdirection only.(3) The second substituent is benzothiazole. It has a big conjugate structure andthe similar atoms to parent material. By VASP calculation, some of its structurecharacteristics can be concluded. Compared with the above two kinds of polymer, ithas more advantages. Energy gap is further reducing, and the hybrid state on density of states increased.At the same time, strength of absorption and reflectioncorresponding increase and decrease in numerical. From the picture of the infraredconductivity, the peak of wavelength is in the range of visible light. This has moreapplicate value than the previous polymers as battery material.We want to achieve certain goals through the study of polythiophene doping..Finally, we find that decreasing its band gap and improving the electron orbitalhybridization can enhance the infrared electric conductivity. By calculation, weshould choose the certain substituent that is with conjugate and also can form the D-Aelectronic structure with the main chain of polythiophene. More substituent can beused to modify conductive polymer in order to improve their conductivity. In later, wecan use the conclusion to guide experiment further.