The Synyhesis And Performance Of Novel Polymers Based On Benzodithiophene And Dithieno Benzothiadiazole

Conjugated polymer solar cells(PSCs)have been widely investigated as one of the potential renewable energy sources with the advantages of such as low-cost,light-weight,flexible and large area through ink-jet printing technology,in comparison with the traditional silicon-based solar cells.We designed,synthesized,and characterized two types of D-A conjunction polymers consisting of BDT and DTBT to explore the relationship between the polymer structure and the photovoltaic performance to get new polymer materials with good photovoltaic performance.Two conjugated polymers(PBDT86-TQ and PBDT88-TQ)with different side chains,but with the same polymer backbone,based on BDT and TQ derivatives have been prepared for polymer solar cells to investigate the importance of side chains on the design of conjugated polymers for high performance polymer solar cells.The side chains in the two polymers induced different steric hindrance.The results showed that the side chains of both polymers have significant effect on the optical,electrochemical,FET and photovoltaic properties though they have the same polymer backbone.PBDT86-TQ showed the 0-0 absorption peak at ~740 nm,and it was blue-shifted to ~660 nm for PBDT88-TQ as a result of strong steric hindrance from two dioctyl chains.Further,the HOMO energy levels of PBDT86-TQ(-5.10 eV)and PBDT88-TQ(-5.54 eV)also showed a large difference.The hole mobility of PBDT88-TQ is ~70 times higher than that of PBDT86-TQ.The photovoltaic cells based on PBDT86-TQ gave a very low PCE of 0.69-0.80%,and for PBDT88-TQ-based cells,the PCEs were improved to 3.70-4.50% with a Voc of up to 0.98 V and improved Jsc and FF.To introduce long polymer chains or branched alkyl chain can increase the solubility,which is advantageous to the solution of polymer solar cells.In addition,the branched chain has a significant effect on the photoelectric properties of conjugated polymers and layer morphology,even change the performance of the photovoltaic devices.Three conjugated polymers based on DTBT with large flat structure have been synthesized.Two electronic thiophene rings are combined with electron-deficient DTBT unit,which can effectively reduce the overall electronic absorption,maintaining high LUMO energy levels.These three conjugated polymers possess bandgaps in the range of 1.67~1.68 eV and exhibit relatively deep HOMO levels between 5.31 eV and 5.42 eV with strong aggregation in room temperature.The polymers are replaced by oxygen group elements.Electronegativity,atomic size of polymer properties and surface morphology have significant effect on the electro-optical properties.The PSC based on PBT-DTBT/PC60 BM has the PCE of 2.85%,the Voc of 0.73 V,and Jsc of 5.64 mA cm-2.For PBT-DTBT/PC60 BM,the high Fill Factor is 0.69.Although because of the solubility of PBS-DTBT and PBO-DTBT,it is hard to form the film during the process of fabricating the devices,but the aggregation behavior and photovoltaic properties,which has undoubtedly a referencing meaning.