The Design, Synthesis And Applications Of Novel Conjugated Polymer Donor Materials Based On Benzo[1,2-b:4,5-b’]dithiophene With Different Side Chain Substituent For Polymer Solar Cells

With the rapid development of human society, the demand of people for energyis increasing. The traditional coal, oil, natural gas and other energy reserves, withfinite existence, easily leading to air pollution and some other shortcomings, are notsuited for a lot of long-term use. Therefore, to find new sources of energy replacingthese traditional energy sources has become the major problem what human societyneed to urgently solve. Solar energy, with its inexhaustible, clean etc. has attachedmuch attention and the technology of utilizing solar energy has been graduallydeveloped. Currently, the tandem inorganic solar cells based silicon and GaAs etc.inorganic semiconductors, the power conversion efficiency of which has reachedmore than40%, are most widely used commercial applications. However, althoughthe technology of inorganic solar cells has made great progress, it also has someobvious deficiencies. For example, when a silicon-based solar cell is fabricated, theoxidation-reduction reaction, used to purified silicon, will waste much energy andcause serious air pollution. Further, the production process of silicon solar cells isrelatively complex and expensive. In order to solve these problems, polymer solarcells have recently attracted significant attention as the most promising technique dueto their potential advantages such as lightweight, flexible nature and are fabricated bya cost-effective manufacturing process. In the continuous efforts of many researchgroups, up to now, the tandem polymer solar cells based on polymer semiconductormaterials have reached a power conversion efficiency of over10%. Nevertheless, it isstill difficult for polymer solar cells to achieve commercial production. Therefore, thereach to improving the power conversion efficiency of polymer solar cell devices hasgreat practical significance and practical value. The research system of this thesis: benzo[1,2-b:4,5-b′]dithiophene which haslarge planar structure and was used as structural unit in most polymer materials whichexhibited high power conversion efficiency was chosen to be polymerized monomerunits to synthesized some novel conjugated polymer materials through the method ofhomopolymerization or copolymerization after introducing different side chainsubstituent. Then, the influence to polymer structure and the different effect topolymer solar cell devices of different side chain substituent are studied by testing thethermodynamic, optical, electrochemical, photovoltaic properties of these polymermaterials.First, a novel monomer is synthesized by introducing the hydrophilic oligomericethoxyl side chain substituent to benzo[1,2-b:4,5-b′]dithiophene unit, and twopolymers are synthesized by homopolymerization with itself and copolymerizationwith alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene. These two polymers have thesame main chain but different side chain. The polymer solar cell devices showdifferent power conversion efficiency for the different roughness and domain size. Atlast, a conclusion that the power conversion efficiency can be lowered by increasingthe percentage of oligomeric ethoxyl side chain substituent is drawed.Second, another novel monomer is synthesized by introducing thehyperconjugated side chain substituent and a polymer is synthesized bycopolymerization with electron-deficient unit. The polymer has conjugated structurenot only along the backbone but also from the backbone to the side chain. As theconclusion, the introducing of conjugated side chain substituent increases the thermalstability, broadens the absorption spectra, lowers the HOMO and LUMO energylevels, and overall, enhances the photovoltaic properties (power conversion efficiencyup to3.57%) of the polymer.At last, Five another polymers based on the above-described monomer withconjugated side chain substituent are synthesized through copolymerization with fiveother units with different strength of electron-deficient power. In conclusion, theHOMO energy levels of the polymers can be effectively regulated by introducing theelectron-deficient unit along the polymer backbone. The different roles of conjugated side chain and the impact on power conversion efficiency of solar cell devices basedon these polymers are explored by studying the basic properties of these polymerswith different HOMO energy levels.