Synthesis And Application Of Benzothiazole And Benzothiophene Based Donor Materials For Organic Solar Cells

Organic solar cell is a kind of photovoltaic technology with great application potential because of its outstanding advantages such as light weight,flexible processing,low cost,and ability to produce large-area devices.It has become a frontier and hot spot in the field of optoelectronic materials at all the world in recent years.Currently,in order to realize the commercialization of organic solar cells,further improvement of its energy conversion efficiency is still a focus issue in this field.This graduate thesis is based on the understanding of the relationship between the structure and properties of photovoltaic materials and aims to improve the existing disadvantages of donor materials.A series of novel efficient difluorobenzothiadiazole and benzodithiophene-based materials are designed and synthesized.Efficient conjugated polymers and small-molecule donor materials have also been explored for the relationship between molecular structure and device performance.Specific research work and results include:1.A series of dithienyl tetrafluorobenzene-based donor polymers?PBT-2TPF4,PffBT-2TPF4?materials were designed and synthesized for high open circuit voltage and high stability polymer organic solar cell devices.A series of high-mobility random polymers spin-coated at room temperature?PffBT-2TPF4-19/1,PffBT-2TPF4-9/1,and PffBT-2TPF4-4/1?were synthesized by random copolymerization.It has been found that tetrafluorobenzene-based polymers have a low HOMO energy level,and therefore beneficial for obtaining a high open-circuit voltage and at the same time being favorable for the stability of the device.By random copolymerization,the aggregation degree of the polymer in the solution and the stacking effect between the molecules are regulated,and thus a high-performance polymer spin-coated at room temperature is obtained,which avoids difficulties broughtaboutbyhigh-temperatureprocessing.Devicesbasedon PffBT-2TPF4-9/1:PCBM as the active layer have a power conversion efficiency of9.4%.Through the non-halogenated solvent,the energy conversion efficiency of9.91%was further optimized.At the same time,the mechanism of the device performance under illumination was revealed through the analysis of the morphology of the active layer film using the synchrotron radiation test method.2.A new thiophene electron acceptor unit?TT-Th?based on ester group was designed and synthesized for the construction of wide band polymer donor materials?PBDT-TT?.It was found that the polymer has a very good symmetry structure,and a face-on stacking structure which favorable for charge transport can be formed under the thin film.In addition,the polymer was constructed by the stragety of using a relative donor unit and a weak electron-deficient.The low HOMO level acompancy with blue absorption of the polymer promote it can be matched with ITIC acceptors that absorb at around 800 nm,and it can also match with near infrared acceptors that absorb more than 900 nm,and both systems exceed 11%energy conversion efficiency,therefore shows a strong application potential.3.A series of A-D-A type small molecule materials?BDT?TBTTT6?₂?BDT?Tff BTTT6?₂?TBDT-T6ffBT?OBDT-T6ffBT?based on benzothiophene as donor unit and benzothiadiazole as acceptor unit were designed and synthesized.The influence of the fluorine atom side chain and the alkane side chain on the photovoltaic performance of the small molecule was discussed.The study found that the introduction of fluorine atoms in the BT unit can effectively regulate the molecular energy level,and its molecular packing is more compact,the mobility is higher,so it has better device performance.But the introduction of fluorine atoms makes its solubility decrease,the addition of alkane side chains on the thiophene bridge ring not only improves its molecular solubility,but also improves its blend morphology with PCBM,resulting in a fibrous nano-interpenetrating network structure,thus further improving the device performance.For the TBDT-T6ff BT:PCBM device,a high energy conversion efficiency of 6.1%was obtained after both additive and thermal annealing treatments.