Design and Synthesis of Novel Organic Photovoltaic Materials Containing Carbon-Nitrogen Unsaturated Bonds for Organic Solar Cells

Author:Cao Cong Cong

Supervisor:cao zuo


Degree Year:2019





In the 21st century,with the rapid development of science and technology,the problems of energy shortages and environmental pollution gradually exposed.As a renewable and clean energy source,solar energy has attracted more and more attention from the scientific community and industry,various photovoltaic technologies have emerged.Among them,organic solar cells have received extensive attention due to their unique advantages such as the ability to prepare flexible devices,solution processing,and large-area production.The performance optimization of organic solar cells is mainly in the two aspects of material development and device optimization.Among them,designing and synthesizing high-performance materials,especially high-efficiency active layer materials,is the basis of organic solar cells.The ideal solar cell active layer material not only needs to have high photoelectric conversion efficiency,but also needs to have the characteristics of simple synthesis method,low cost,large-scale production and environmental friendliness.Need to comprehensively consider synthetic routes and synthetic methods when designing the high efficiency organic solar cell active layer materials.In the paper,we mainly use new synthetic methods to prepare active layer materials for organic solar cells.A series of conjugated polymer and small molecule was prepared and the photovoltaic performance was researched.Knoevenagel condensation reaction is an environmentally friendly non-metal catalyzed dehydration condensation reaction which is carried out by base-catalyzed reaction of an aldehyde group-containing monomer with an active methylene-containing monomer.It has the advantages of simple post-treatment,simple synthesis of reaction monomers,easy purification,non-toxicity,high atomic economy and no metal catalyst.In the second chapter,A series of A-D-A type near-infrared small-molecular acceptors receptor with the indacenodithiophene(IDT)as the core was synthesized by Knoevenagel condensation reaction,the dithiophene ethylene or dithiophene acrylonitrile was used as bridges.It was found that,through the introduction of the strong electron-withdrawing cyano group on the double bond,the HOMO level of the molecule is deepened.The HOMO level of the molecule is further deepened by introducing a fluorine atom at the terminal group.Finally,a near-infrared small molecule acceptor material with an absorption edge of 1022 nm was obtained,the photoelectric conversion efficiency of 2.64%was obtained for organic solar cell.In the third chapter,we prepared the dialdehyde-containing monomers and diacetonitrile-containing monomers,a series of benzodithiophene(BDT)-based copolymers were prepared by Knoevenagel condensation reaction under the catalysis of potassium tert-butoxide.Through the optimization of main chain and side chain,the optical and electrochemical properties was improved.The corresponding organic solar cell device with a photoelectric conversion efficiency of 8.54%was obtained when matching with ITIC.Besides,it was found that polymers prepared by two polymerization methods of Knoevenagel condensation reaction and Stille polymerization has no significant difference in physical and chemical properties and photovoltaic performance.In the fourth chapter,organic conjugated small molecules containing carbon-nitrogen unsaturated bonds was synthesized by Schiff-base reaction.PDI dimers containing imine groups was synthesized through Schiff-base reaction from perylene tetracarboxylic acid anhydride by losing one equivalent of water.The target compound has good thermodynamic stability,good optical electrochemical performance and photoisomerization.It is used as an acceptor material for organic solar cells with an efficiency of 4.34%.In the fifth chapter,polymers containing carbon-nitrogen unsaturated bonds were synthesized by Schiff-base reaction,which were used as organic solar cell donor material.The copolymers have good thermal stability,strong absorption spectrum in the ultra-visible region,and good electrochemical properties.The effect of the introduction of fluorine atoms on the photoelectric properties of the polymer on the acceptor unit was also studied.The introduction of fluorine atoms can effectively enhance the charge transfer in the polymer molecule,enhance the aggregation behavior between the main chains of the molecules,and effectively deepen the HOMO level of the copolymer.In the sixth chapter,copolymer donor materials containing the naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole(NT)unit was synthesized.Deepening the HOMO level of the polymer by introducing a carboxylate in the side chain,thereby increasing the VOCC of the devices.Two donor(D)units with different electron donating capabilities,thiophene and dithiophene,were selected to constructing the main chain structure of the copolymers.The copolymer obtained with thiophene as the D unit has a deeper HOMO level,and the VOCC of the corresponding device can reach to 0.92 V.The copolymer obtained by using dithiophene as the D unit has a broader absorption spectrum,strongerπ-πstacking between the molecules,and the polymer has obvious temperature-changing absorption characteristics,but the HOMO level of the polymer becomes shallower.The corresponding device has a VOCC of only 0.76 V.Terpolymers with different content of carboxylate side chain were synthesized and compared with the corresponding binary copolymers.By comparing several polymers,we found that when the carboxylate side chain content is 25%,the optical properties and electrochemical properties of the polymer are the best,and the corresponding device performance is also the best.