Synthesis And Characterization Of Two-dimensional Conjugated Polymer Donor Materials With Bisalkylthio Side Chain Substituent

In the last decade,polymer solar cells have been studied extensively and shown great progress with power conversion efficiencies（PCEs）exceeding 11%,presenting great potentials in practical applications.The side-chain engineering of polymer can effectively tune the photovoltaic performances,the length or conformation of alkyl side chains strongly affect the properties of polymers,such as the physicochemical properties or the interaction between the polymers and acceptor materials.In this dissertation,seven donor-acceptor conjugated polymers modified with different length or numbers of alkylthio side chains were successfully synthesized.Their thermal,optical,electrical,crystalline properties and photovoltaic performances have been systematically investigated.（1）To reveal the effect of bisalkylthio side chain length,four polymers PBDTT-DS1-BTff,PBDTT-DS2-BTff,PBDTT-DS3-BTff and PBDTT-DS4-BTff based on different bisalkylthio substituted thienyl-benzodithiophene（BDTT-DS）donor units and(5,6-difluoro-4,7-di（thiophen-2-yl）benzo[c][1,2,5]thiadiazole（BTff）acceptor unit have been obtained and studied.The polymers showed different absorption maxima（λmax）,which indicated a different aggregation behavior.All polymers demonstrated deep HOMO energy levels（<-5.51 eV）,correspondingly resulting in high VOC.The devices based on PBDT-DS2-BTff exhibited the highest PCE of 5.82%,with a Jsc of 11.06 mA cm-2,a VOC of 0.92 V and a FF of 57.2%.In chapter 2,the results revealed that the length of bisalkylthio side chain can greatly impact the polymer’s self-assembling properties,solubility,the miscibility with fullerene acceptor and the device’s efficiency.（2）Three polymers PBDTT-DS2-FBTz、PBDTT-DS4-FBTz and PBDTTs-FBTz were designed by incorporating two-dimensional benzo[1,2-b:4,5-b’]dithiophene with different alkylthio side chains as donor units and 4,7-dibromo-2-（2-ethylhexyl）-5,6-difluoro-2H-benzo[d][1,2,3]triazole（FBTz）as acceptor unit.These polymers showed wide optical bandgaps of～1.90 eV,good solubility and crystallization properties.Also,the devices based on them demonstrated a high VOC（>1.00 V）,and without any optimization,the devices based on PBDTTs-FBTz exhibited the highest PCE of 2.43%,with a VOC of 1.01 V,aJscof 6.40 mA cm^-2,and a FF of 38.0%.