Synthesis And Photovoltaic Performance Of Multiple-component Copolymer Donor Materials

With the increasing depletion of fossil resources,the demand for various new energy materials is increasing.As a photovoltaic cell with light weight,flexible device,easy modification and other excellent characteristics,polymer solar cells have been extensively studied by domestic and international scientific researchers.In recent years,the development of polymer solar cell(PSC)has been extensively increased.The emergence of a variety of new donors and acceptors has updated the PCE records many times,and the energy conversion efficiency(PCE)has already over 18%.In order to enhance efficiency of polymer solar cells,an effective and concise method is to make multiple-component copolymer donor materials,a third component(D'or A'unit)was add into the D-A type copolymer to form conjugated D-A-D'-A or D-A-D-A'terpolymers,this will provide a simple and cost-effective method to improve their light absorption and adjust the energy level,and can modulate the inter-chain packing and the solubility of materials.In addition,the reasonable control of the stoichiometric ratio of these components in the multiple-component copolymer also provides a way to further optimize these factors,so that high-performance PSC could be obtained.Here,we designed three series of multiple-component copolymer donor materials,using nuclear magnetic resonance,mass spectrometry and GPC etc methods to characterize and confirm the synthesized monomers and copolymers,and using ultraviolet-visible absorption spectroscopy,cyclic voltammetry and other methods to confirm their photophysical and electrochemical performances.According to their properties,suitable acceptors were selected for matching the donors,and the OSCs based on these donor materials were prepared to study their photovoltaic performances.The main contents of this dissertation are as follows:1.Designed and synthesized a novel electron-donating unit M1 by connected truxene with triphenylamine,then copolymerized M1 with a thiophene?bridge containing benzothiadiazole electron-deficient unit(DTBT)to obtain a binary copolymer P1 by stille coupling copolymerization;Simultaneously,M1,dithiophene-benzothiadiazole(DTBT),benzodithiophene(BDT)and benzodithiophene dione(BDD)are copolymerized to obtain a quaternary copolymer P2.The performances of the two copolymers are systematically studied.The introduction of BDT and BDD made P2 possess wider absorption on the basis of P1,increased its visible light absorption intensity,displayed a lower HOMO energy level,and increased the hole and electron mobility of its device.The OSCs devices based on copolymer donor P1 and P2 and non-fullerene small molecule acceptor Y6 as the active layer achieved PCE of 1.25%and 8.31%,respectively.2.Designed and synthesized the electron-donor building-block benzo[1,2-b:4,5-b']dithiophene(BDTP)with alkyl chlorophenyl side chain,copolymerized BDTP with fluoroalkyl thienyl side chain benzo[1,2-b:4,5-b']dithiophene electron-donor(BDTT)and thiophene?bridge benzo[1,2-c:4,5-c']dithiophene-4,8-diketone electron-deficient building-block(BDD)by Stille coupling copolymerization,and three donor copolymers with different ratios of electron-donating unit and electron-deficient unit were obtained.The study found that the increase of the BDTP component is not conducive to its spectral absorption,and ultraviolet-visible absorption has blue shifted.The electron and hole mobility of devices turn to reduce,resulted in lower short-circuit current density(J_sc)and fill factor(FF)of the photovoltaic device,but the open circuit voltage(V_oc)is increased;The three copolymers are used as the electron donor material,the small molecule acceptor Y6 is used as the electron acceptors to make OSCs.The PCE values of polymer solar cell devices based on P3,P4 and P5 are 7.55%,9.89%,and 9.57%,respectively.3.Three ternary copolymers containing DTBT side chains were designed and synthesized,and the influence of the different ratios of the electron-deficient building-block A on main chain and electron-deficient building-block A on side chain on the properties of the donor material was studied.The introduction of DTBT on side chain regulates effectively the photophysical properties.With the increase of side chain monomer DTBT,the V_ocof copolymer-based OSCs is improved,but a larger amount of DTBT on side chain affect the orderness of the molecular packing and reduces the mobility of holes and electrons,so that both J_scand FF are reduced.When the ratio of the electron-deficient building-block A on main chain to the electron-deficient building-block A on side chain is 3:1 in the terpolymer,the best photovoltaic performance is obtained,and the PCE value is 2.87%.