Synthesis And Photovoltaic Properties Of Boron Dipyrromethene And Benzothiadiazole Donor Materials

With the effort of academia and industry,photovoltaic technology that obtains electricity from sunlight has been achieved and regarded as one of the cleanest and renewable energy sources of the next generation.Currently,the main active materials of solar cell in the market are crystalline silicon and inorganic semiconductor materials.Organic materials are relatively few,but organic materials have been widely concerned by researchers because of their unique advantages.Based on the relationship between the structure and performance of organic photovoltaic materials,a series of novel conjugated polymers and small molecule donor materials based on fluoroborodipyrrole and benzothiadiazoles were designed and synthesized to improve their existing deficiencies.At the same time,the exploratory research analysis of the relationship between molecular structure and device performance was carried out.The main research contents are as follows:(1)Four new D-A conjugated donor polymers,BDH1-4,were synthesized using fluoroborodipyrrole as the acceptor unit and benzodithiophene and dithiosilanol as the donor unit.Through the study of photophysics and chemical property of polymer materials,it is found that the introduction of conjugated units in the main chain of the polymer can more effectively improve the light absorption performance compared to the introduction of conjugated units in the polymer side chain,thereby improving performance of cells.Among the four polymers,BDH3 has better planarity than the other three polymers,but its efficiency is very low because of its high aggregation degree as active layer material.Therefore,the shape of the morphology plays a vital role in the efficiency of the device.Among them,the introduction of thiophene units in the main chain and BDH4 with a relatively good morphology has a higher power conversion efficiency of 3.69%.(2)Novel A-D-A small molecule donor material was constructed using benzodithiophene as the donor unit,thiophene as the bridge,and benzothiadiazole substituted with different fluorine atoms as the acceptor unit.Through the study of the photophysical and chemical properties of small molecule materials,it was found that the absorption range of fluorine atoms is slightly reduced after the introduction of fluorine atoms in the benzothiadiazole acceptor unit,but the strong electronegativity of fluorine atoms increases the molecular push and pull effect.Thereby enhancing the charge transfer within the molecule.At the same time,the introduction of fluorine atoms also reduces the HOMO energy level of the donor material,which makes the device have a higher open circuit voltage.However,the introduction of different numbers of F atoms has different effects on the mixed morphology of the material.Among them,SBDT2 has a flatter surface and proper phase separation,which makes it have a higher short-circuit current and an efficiency of 5.06%.(3)Three new D-A conjugated donor polymers were constructed using chlorobenzodithiophene as the donor unit,benzothiadiazole as the acceptor unit,and different amounts of thiophene as the?interval.Studies on the photophysical and chemical properties of polymer materials have revealed that all chlorinated polymers exhibit low HOMO energy levels.With the introduction of thiophene,the HOMO level of the molecule increases first and then decreases,and its open circuit voltage also has the same trend.At the same time,the introduction of thiophene greatly increased the solubility of the material,making it better spin-coated into a film and having a higher Jsc.The device based on PBDBT-1:PC₇₁BM obtained a power conversion efficiency of5.73%after simultaneous treatment with additives and thermal annealing.