Design And Synthesis Of Non-fullerene Active Materials For Organic Photovoltaic Solar Cells

Since the beginning of the new century,in order to meet the globally developing economy and the improvement of people's living standard,human beings only exploit fossil energy such as coal,oil,which not only causes the problems of energy shortage,but also leads to environmental pollution.Therefore,it is urgent to find alternative clean renewable energy.Organic solar cells have many advantages,such as easy access to raw materials,low cost,light weight,easy processing,and adjustable photovoltaic properties,which have attracted extensive attention from scientists.In bulk heterojunction solar cells,active layer materials are the hot sopt.The active layer materials are divided into two parts:acceptor materials and donor materials.The common development of the two materials greatly improves the performance of organic photovoltaic cells.In this paper,a diketopyrrolopyrrole small molecule acceptor with biphenyl core and two benzodithiophene-benzothiazole polymer donors introducing chlorine atoms with different substituent positions were designed and synthesized from donor and acceptor two kinds of materials.We respectively characterized their optical and electrochemical properties and fabricated corresponding organic photovoltaic cells,discussing the relationship between structure and photovoltaic performance from two aspects of donor and acceptor materials.The specific works are summarized as follows:In the first research system,a diketopyrrolopyrrole small molecule acceptor with biphenyl core?BP?DPPB?₄?was designed and synthesized,and a diketopyrrolopyrrole small molecule acceptor with spirobifluorene core?SF?DPPB?₄?was synthesized for comparison.We characterized their thermal,optical and electrochemical properties.All organic photovoltaic devices based on BP?DPPB?₄and SF?DPPB?₄were fabricated using P3HT as donor material.The effects of annealing temperature on the performance of the devices based on BP?DPPB?₄were well studied,and the relationship between two structures with different size cores and the photovoltaic performances of corresponding devices was discussed.The results indicated that when the annealing temperature reached the glass transition temperature of 120 ^oC,the device based on BP?DPPB?₄achieved the highest 1.43%efficiency.By comparing the organic photovoltaic cells based on BP?DPPB?₄and SF?DPPB?₄,we can find that SF?DPPB?₄with a larger core had correspondingly better photovoltaic performance.This result indicates that the introduction of the larger sizes of three-dimensional hydrocarbon aromatic core is the effective strategies to improve the photovoltaic performance of the devices based on diketopyrrolopyrrole small molecule acceptors.In the second research system,two benzodithiophene-benzothiazole polymer donors with chlorine atoms at different substituent positions?3'-J52-2Cl and 4'-J52-2Cl?were designed and synthesized.We characterized their thermal,optical and electrochemical properties.The results showed that the 3'-J52-2Cl with the 3-site substitution of?-bridged thiophene exhibited a more torsional configuration and the molecule had a greater steric hindrance effect,which resulted in a blue shift absorption spectra and a deeper the highest occupied molecular orbital?HOMO?level.All organic photovoltaic devices based on3'-J52-2Cl and 4'-J52-2Cl were fabricated using ITIC as acceptor material.The relationship between the molecular structures with different chlorine atoms substitution positions and the photovoltaic performance was investigated.Due to the smaller steric effect of the polymer 4'-J52-2Cl,the photoelectric conversion efficiency of the corresponding device was significantly improved to 6.67%,but the efficiency of3'-J52-2Cl device was only 0.03%.This work showed that the 4-site substitution of?-bridged thiophene facilitated the whole molecule to have a smaller steric hindrance effect,resulting in improved performance of organic photovoltaic cells.This conclusion has certain guiding significance for the future research on the modification of chlorine atoms in the active layer materials of organic photovoltaic devices.