The Development Of Bis-thiophene Vinyl Side Chain Conjugated Polymers/CdS-based Photovoltaic Materials And Devices

Benzo [1,2-b:4,5-b'] dithiophene(BDT)is typically used as a building block for the polymer donor material,because it has symmetric planar structure,strong ?-? stacking effect and relatively high hole mobility(0.25cm2V-1s-1).Dithiophene vinyl group is conductive to carrier transmission has the advantages of large conjugation degree and narrow band gap and so on.So we synthesized a donor unit with a greater conjugated degree and good solubility,namely 4,8-bis[(5)-((E)-2-(4,5-decylthiophen-2-yl)vinyl)thiophen-2-yl]benzo[1,2-b:4,5-b'] dithiophene(BDT-TVTC10)by introducing dithiophene ethylene side chain groups at the 4 and8 positions of benzo [1,2-b:4,5-b'] dithiophene(BDT)as electron donor unit in this paper.And we synthesized a series of new D-A conjugated polymers with different electron acceptor units.And CdS has a high electron mobility and environmental stability.Therefore,a photovoltaic device with structure of ITO/CdS(or PFN)/Polymer: PC61BM(or PC71BM)/MoO3 /Ag was prepared by using CdS and PFN as the cathode transport layer.What's more,we studied the structures and photovoltaic properties.The main contents of this thesis are as following:1.Chapter 2,we synthesized a electron donor unit,namely,4,8-bis [5-((E)-2-(4,5-decyl-thiophen-2-yl)vinyl))thiophen-2-yl]benzo[1,2-b:4,5-b']dithiophene(BDT-TVTC10),taking2-bromo-3-decylthiophene and 2-methylthiophene as raw material.By Stille coupling reaction between the above mentioned monomers and 3,7-bis(2-bromo-3-octylthiophen-5-yl)-naphtho[1,2-c:5,6-c']-bis[1,2,5]thiadiazole,we got conjugated polymer,namely BDT-TVT-DTNTC8.The resulted copolymer of BDT-TVT-DTNTC8 showed the absorption band edge of 817 nm in thin film and the optical band gap was 1.52 eV,EHOMO and ELUMO were-5.36and-3.84 eV.When the structures was ITO/CdS/PBDT-TVT-DTNTC8: PC71BM(1:1,3%DIO)/MoO3/Ag,the highest PCE was 2.29%(VOC=0.71 V,JSC=6.70 mA/cm2,FF=48.10%).When the device was prepared by using PFN as cathode transport layer and PBDT-TVT-DTNTC8 : PC71BM(1: 1,3% DIO)as active layer,the highest PCE was 3.21%(VOC=0.74 V,JSC=9.15 mA/cm2,FF=47.63%).2.Chapter 3,since the lactam group(O=C-NR)is an electron-deficient group and the solubility of the polymer can been improved by introducing an alkyl chain on the N atom,two electron acceptor units containing an O=C-NR structure were synthesized,namly6,6'-dibromo-N,N'-(2-butyloctyl)-isoindigo(IDBOBr2)and 2,5-2-hexyldecyl-1,4-dioxoygen-3,6-bis(5-bromothiophene)-pyrrole[3,4-c] pyrrole(DPPHDBr2)in this chapter.Then two conjugated polymers of PBDT-TVT-IDBO and PBDT-TVT-DPPHD were synthesized respectively by stille coupling reacted with the electro-donating monomer BDT-TVTC10.The absorption band edge of PBDT-TVT-IDBO and PBDT-TVT-DPPHD were about 760 and 839 nm in thin film.The optical band gap were about 1.63 and 1.48 eV,EHOMO were-5.45and-5.33 eV,ELUMO were-3.82 and-3.85 eV.When the structures was ITO/CdS/PBDTTVT-IDBO: PC61BM(1:1.5,3% DIO)/MoO3/Ag,the highest PCE was 0.52%(VOC=0.83 V,JSC=1.59 mA/cm2,FF=39.79%).When the structures was ITO/PFN/PBDT-TVT-DPPHD:PC61BM(1:1.5,3% DIO)/MoO3/Ag,the highest PCE was 0.76%(VOC=0.72 V,JSC=1.93 mA/cm2,FF=55.21%).3.Chapter 4,we synthesized [1,2,5]thiadiazole(BT),which has the advantages of strong electron-with drawing ability,simple synthesis and good air stability.And the other electron acceptor unit 5,6-difluoro [1,2,5] benzothiadiazole(FBT)was synthesized by introducing fluorine atom into the BT to reduce the HOMO level which can increase the open circuit voltage of the polymer.By stille coupling,BDT-TVTC10 reacted with benzo[1,2,5]thiadiazole and 5,6-difluorobenzo[1,2,5]thiadiazole respectively,then got two polymers of PBDT-TVT-BT and PBDT-TVT-FBT.The polymers have good thermal stability and solubility.The absorption band edge of PBDT-TVT-BT and PBDT-TVT-FBT were about 799 and 732 nm in thin film.The optical band gap were about 1.55 eV and 1.69 eV,EHOMO were-5.18 and-5.38 eV.That means,the introduction of fluorine atoms reduced the HOMO level of the polymer significantly.ELUMO were-3.63 and-3.69 eV.When the structures was ITO/CdS/ PBDT-TVT-BT:PC61BM(1:2,3% DIO)/MoO3/Ag,the PCE was 0.23%(VOC=0.69 V,JSC=1.04 mA/cm2,FF= 31.89%).When the structures was ITO/CdS/PBDT-TVT-FBT:PC61BM(1:2,3% DIO)/MoO3/Ag,the PCE was 0.36%(VOC=0.76 V,JSC=1.33 mA/cm2,FF=35.99%).That is,by introducing the fluorine atoms,then open circuit voltage and power conversion efficiency of the device have been improved.