The Preparation And Photovoltaic Properties Of Benzondifuran- Benzodifurandione Based Polymers

With the development of global economy and population growth,the demand for energy is increasing.Fossil fuels such as coal and oil are not only going to be depleted,but will also be accompanied by a lot of environmental pollution during their use.In order to ensure the sustainable development of society,it is very important to find a clean and renewable energy.Solar energy is an inexhaustible clean energy.If we can effectively use solar energy,the energy crisis will be solved easily.Solar cells are devices that convert solar energy directly into electrical energy.Polymer solar cells have good application prospects because of the advantages of low cost,wide material source,light quality,good flexibility,simple preparation process and large area production by solution processing methods.At present,most polymer solar absorbing layer materials are based on thiophene.However,thiophene is extracted from petroleum chemical industry,which not only has high extraction cost but also has a large environmental pollution,which restricts the large-scale application of thiophene polymer solar cells.Therefore,it is of great practical significance to find a new efficient and environmentally friendly polymer donor material.Furan has a thiophene like molecular structure,and furan has a wide range of sources,and can be fermented by straw,vegetable leaves and other plants,which is friendly to the environment.Although furyl polymer has shown excellent photovoltaic performance in polymer solar cells,there is still less research on furyl polymer solar cells.In this paper,a series of new Benzo[1,2-b:4,5-b′]-difuran-Conjugated polymers were designed and synthesized.Their optical and electrochemical properties were characterized.Four kinds of polymer solar cell devices such as PBDFC-BDD,PBDFS-BDD,PBDFS-F-BDD and PBDFS-F-BDD were prepared with PB71 CM as the acceptor materials,and their photovoltaic performance was studied.The specific work is as follows:In order to enhance the absorbability of polymer materials and to compare the effects of different alkyl side chains on the properties of furanyl polymers,the alkylfuranofuran side chain and alkyl furan side chain were introduced into the Benzo[1,2-b:4,5-b′]-difuran(BDF)donor unit and together with the 1,3‐bis(5‐bromothiophen‐2‐yl)‐5,7‐bis(2‐ethylhexyl)‐4H,8H‐benzo[1,2‐c:4,5‐c′]dithioph ene‐4,8‐dione(BDD)receptor unit,two polymer donor materials PBDFC-BDD and PBDFS-BDD were obtained.The effects of the change of polymer side chain on the thermal properties,optical properties,electrochemical properties,molecular configurations,molecular stacking behavior and photovoltaic properties of polymers were systematically analyzed.The energy conversion efficiency of 3.48% and 3.01% of the solar cell devices,PBDF-S-BDD:PC71BM and PBDF-S-BDD:PC71BM,prepared by two kinds of polymer materials,was obtained under a series of optimized conditions.In order to explore the effects of the alkyl chain on the pion bridge and the heteroatoms of different electrons on the energy level,absorption spectrum,aggregation behavior and the performance of photovoltaic devices,three new types of D-A polymers,PBDFS-T-BDD,PBDFS-F-BDD and PBDFS-S-BDD,were designed and synthesized.The optical properties of the polymers are characterized.It is found that after changing the sulfur atoms on the pion bridge into oxygen atoms,the band gap of the polymer is narrowed,and the band gap of the polymer is broadened when the alkyl side chain is introduced on the PI bridge.PBDFS-F-BDD and PBDFS-T-BDD were used as donor materials and PC71 BM receptor materials prepared into solar cell devices,the two devices are respectively achieved 2.32% and 2.03% of the energy conversion efficiency.