Synthesis And Performance Characterization Of Crosslinkable Low-bandgap Conjugated Polymers Based On Benzo[1,2-b:4,5-b'] Dithiophene

With environmental pollution becoming more and more serious,the related research on green and clean solar energy sources is the research hotspot,and the research of solar cells is favored by the scientific research community.Traditional inorganic solar cells have many shortcomings,such as complex preparation process,high cost,and difficult to prepare large area devices.Therefore,the advantages of polymer solar cells(PSCs)are light weight,relatively simple preparation process,good flexibility,and the ability to fabricate devices in large areas.Therefore,the PSCs have become one of the hot spots in current research.After rapid development in recent years,the power conversion efficiency of polymer solar cells has exceeded 14%,showing excellent application potential.In this thesis,crosslinkable polymers are synthesized with the benzo[1,2-b:4,5-b']dithiophenen as the rich electron,and four kinds of random polymers are synthesized with dithieno[2,3-d:2',3-d']benzo[1,2-b:4,5-b']dithiophenen(DTBDT)as the electronic units.The polymer donor materials of different structures have an effect on the thermal stabilities,lightabsorbing ability,film-forming ability,energy-level structure,aggregation behavior,performance characterization of crosslinkable polymers,active layer morphology,and photovoltaic device performance as the active layer of polymer solar cells in this dissertation.Firstly,by the Stille coupling reaction,2,6-bis(trimethylstannyl)-4,8-bis[4-octyl-5-(7-octenyl)-thiophene-2-yl]-benzo[1,2-b:4,5-b']dithiophene(TOESn)and 1,3-bis(5-bromothiophen-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione(T1Br2)were used to synthesize conjugated polymer containing a double bond,namely PCL-TI.The crosslinkable group 1,8-octanedithiol(ODT)was introduced into the side chain of polymer PCL-T1 containing a double bond,and the crosslinked polymers film formed under UV light irradiation that had better network interpenetrating structure and good solvent-resistant.The optical band gap(Eg)of polymer PCL-T1 was 1.90 e V,the highest molecular orbital energy level(EHOMO)was-5.52 e V,and the lowest molecular unoccupied orbital energy level(ELUMO)was-3.62 e V.The photovoltaic devices were fabricated with the structure of ITO/PEDOT:PSS/active layer/PEN/Al,and the optimal device based on PCL-T1 and PC71 BM mass ratio of 1:1.5 exhibited 1.53% in power conversion efficiency(PCE).The PCL-T1,ODT and PC71 BM mass ratio of 1:1:1.5 were mixed and crosslinked under UV light irradiation as active layer,and its PCE was 1.27%.Secondly,two conjugated polymer,namely PCL-DTNT and PCL-FTT were synthesized by the Stille coupling polymerization method,based on TOESn as donor moiety and 4,9-bis[5-bromo-4-(2-ethylhexyl)thiophene-2-yl]naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole(DTNTBr2)or 2-ethylhexyl-4,6-dibromo-3-fluorothieno[3,4-b]thiophene-2-carboxylate(FTTBr2)as acceptor unit.The Eg of the polymers PCL-DTNT and PCL-FTT were 1.61 e V and 1.68 e V,EHOMO were-5.15 e V and-5.43 e V,ELUMO were-3.54 e V and-3.75 e V,respectively.The optimal device based on PCL-DTNT and PC71 BM mass ratio of 1:1 as active layer exhibited 4.08% in PCE.When the mass ratio of PCL-DTNT,ODT and PC71 BM was 1:1:1 and crosslinked under UV light irradiation as active layer,the PCE was 3.67%.The optimal device PCE based on PCL-FTT and PC71 BM mass ratio of 1:1 was 1.41%,and the PCL-FTT,ODT and PC71 BM mass ratio of 1:5:1 was mixed and crosslinked under UV light irradiation as the active layer with a PCE of 0.41%.Thridly,we had previously studied the properties of polymers without alkylthiophene spacers and with two alkylthiophenes spacers.In order to study the effect of alkylthiophenes spacers and fluorine atom on polymer properties systematically,we designed and synthesized the random polymers with one alkylthiophene spacer,namely PDTBDT-SBT,PDTBDTSBTEH,PDTBDT-SFBT,and PDTBDT-SFBTEH.And the insertion of alkylthiophene spacers and fluorine atom into to the polymer backbone had an influence on the thermal stabilities,the energy level,absorption spectra,aggregation behavior,light stability,photovoltaic device performance of the polymers.