Study On The Synthesis And Characterization Of Regioregular 3-substituted Polythiophenes As Electron Donor In Polymer Solar Cell

As one of the most promising field of polymer solar cells, polythiophene-based conductive polymers have received plenty of attention from scientists all over the world. The absorption ability and hole carrier mobility of conjugated polymers are critical parameters to evaluate power conversion efficiencies of polymer solar cells. In addition, stability under atmosphere environment is another key factor for consideration. Based on the aforementioned background, we designed new conductive polymers from the perspective of molecular structure:3-substitued polythiophene with different groups were synthesized to improve polymer stability in the air, and through adjustments of band gap, the scope of absorption spectrum was increased. After which, the future application of polythiophene on solar cells became more possible.1. Regioregular poly(3-hexylthiophene) was synthesized by exchanging with Grignard agent followed by coupling with catalysis of Ni(dppp)Cl2. A nearly 100% HT-HT structure was verified from 1H NMR data analysis. This highly regioregular structure gives PHT outstanding stability and certain redshift of absorption spectra was found in contrast to materials with lower regioregularity.2. Carboxylate was successful introduced to side chains by careful formation of the mono-Grignard reagent from octyl 2,5-dibromothiophene-3-carboxylates at-40℃for 1 h followed by nickel-catalyzed polymerization, The obtained poly(octyl thiophene-3-carboxylate) also shows high regioregularity (HT-HT structure) and distinguished thermal stability. HOMO energy level was also reduced by minimizing the level of p-doping by ambient oxygen through the incorporation of electron-withdrawing substitute, viz. carboxylate.3. To further enhance the stability and reduce band gap, Polythiophene block copolymer was prepared using Stille coupling reaction catalyzed by Pd(PPh₃)₄. The product, Poly(3-octylthiophenecarboxylate-co-thiophene), shows a good stability from TG and UV analysis, and band gap of this material is also reduced.