Design,Synthesis And Photovoltaic Properties Of Small Molecule Donors Based On Porphyrin And Benzothiadiazole

With the rapid development of modernization,the problems of energy shortage and environmental pollution have become more and more serious,and the conversion of solar energy into electricity can be an effective way to partially solve the energy problems.Organic solar cells have received extensive attention in recent years due to their advantages of low cost,solution processing,flexibility and light weight.The preparation process of ternary organic solar cells is simple,and the components in the active layer usually have complementary absorptions,which can make more use of sunlight and show great commercial application prospects.Porphyrins are widely used in the preparation of organic photovoltaic materials due to their strong light absorption,good planarity and easy modification,showing excellent photovoltaic properties.This dissertation focuses on the design,synthesis and properties of benzothiadiazole and porphyrin based donor materials,and their applications in OSCsIn Chapter 2,we designed and synthesized three novel A-π-A-π-A small molecules with strong electron-withdrawing unit benzothiadiazole as the core,3-octylrhodanine as the end-capping unitsπ-bridged with different numbers of thiophene units.We found that the length of theπbridge has a great influence on the energy level of the molecule,π-πaggregation and electron push-pull effect.Though the binary solar cells based on these molecules with PTB7and PC₇₁BM respectively show very poor device performance,the ternary devices based on PTB7:PC₇₁BM with BT2TR and BT3TR as the third component exhibit power conversion efficiencies of 9.30%and 9.21%respectively,which are enhanced by 17%and 15%compared with that of the PTB7:PC₇₁BM binary solar cells,indicating that A-π-A-π-A small molecules are promising on ternary solar cells.In chapter 3,we synthesized three porphyrin molecules with D-A,A-D-A and D-A-D configurations by using benzothiophenonedione as the electron-withdrawing group and linking it with porphyrin ring by alkyne bond.We systematically studied the effects of configuration changes on the absorption,electrochemical and photovoltaic properties of the molecules,and that the molecule with A-D-A configuration has the strongest intramolecular charge transfer effect and the best photovoltaic performance.In Chapter 4,we introduced fluorine atoms into porphyrin side groups.The effects of fluorine atoms on molecular aggregation,energy levels and absorption spectra were studied.The introduction of fluorine atoms can reduce the energy levels of the molecules,which increases the open-circuit voltage from 0.72 V to 0.85 V.In addition,the absorption ability of molecules to solar light will not be weakened.In Chapter 5,we designed and synthesized porphyrin dimers with a solar absorption threshold of 1000 nm,and explored the effects of the conjugation length of the molecule on the molecular aggregation,absorption and fluorescence spectra.We found that reducing the addition of pyridine and using cathode with low work function has a positive effect on device performance under the premise of ensuring dissolution.The efficiency of devices based on BT2PTR increases to 5.62%,and the current reaches 15.02 mA cm^-22 after SVA treatment.