Synthesis And Photovoltaic Application For Conjugated Polymers Based On Thieno[3,4-c]Pyrrole-4,6-dione

As the third generation solar cells,polymer solar cells(PSCs)have attracted considerable attentions due to their low device fabrication cost,mechanical flexibility and large-area production through solution processing.Thieno[3,4-c]pyrrole-4,6-dione(TPD)unit possesses a simple structure,which could be synthesized easily and utilized as electron-withdrawing co-monomer.The formation of "supramolecular locks" have been widely observed in TPD based polymers,which could facilitate the mainchains of the conjugated polymers to be more planar.At the same time,the push-pull structures will reduce the optical bandgaps for the polymers.In this thesis,a series of novel polymers were prepared based on TPD unit,difluorobenzothiadiazol(ffBT)unit and 4,9-bis(bis(4-hexylphenyl)methylene)-4,9-dihydro-s-indaceno-[1,2-b:5,6-b']bis(selenophene)(DPMIDSe)unit.The relationships between the structures and the photovoltaic performances were investigated and the details are as following:Part ?:The study of the synthesis and photovoltaic properties of conjugated polymers based on TPD unit via construction of supramolecular conformation locksBased on TPD unit and ffBT derivatives,a serials of conjugated polymers,namely PBT-TPD-nT(n = 2,4 and 6),were designed and synthesized by adjusting the number of thiophene bridges between the two electron deficient units in the conjugated backbones.Their UV-vis properties,electrochemical properties and photovoltaic performances were investigated and discussed.Through the UV-vis spectras,we can clearly see that three polymers all have only one main absorption band at 400-750 nn,indicating that they are narrow bandgap polymers.The cyclic voltammetry(CV)reveals that the HOMO levels of PffBT-TPD-2T,PffBT-TPD-4T and PffBT-TPD-6T are-5.91 eV,-5.68 eV and-5.47 eV,respectively.Finally,the bulk heterojunction cell devices were assembled with the copolymers used as the donors and fullerene derivative(PC71BIM)as the acceptor.The results showed that the HOMO,short-circuit current density(Js.)and fill factors of the three polymers elevated with the increasing numbers of thiophene units,but the open-circuit voltage(Voc)presents an opposite trend.All of the experimental results demonstrated that adjusting the numbers of thiophene can effectively tune the light-harvesting abilities and the efficient exciton separation.The preliminary results for the device fabrication revealed that the PBT-TPD-6T showed a best performance of power conversion efficiency(PCE)of 5.6%(Voc= 0.73 V,Jsc?10.83 mA/cm2,FF=71%)among these polymers.Part II:The study of the synthesis and photovoltaic properties of conjugated polymers based on ethylene modified IndacenodiselenopheneIn this part,we designed a new aromatic ladder typed electron donating building block,which introduced two ethylene side chains onto the indacenodiselenophene and it's named as DPMIDSe.In order to extend the absorption spectra of the final materials,two sp2 hybridization chains were grafted at the side direction from the main conjugated cores.In addition,the introduction of Se heterocyclic untis will improve the carrier transportation and lead to enhanced photovoltaic performances.In this part,TPD was also chosen as the electron deficient co-monomer in the conjugated polymer construction in order to generate coplanar mainchains induced by the supramolecular locks produced by the TPD units.The as-synthesized polymers were prepared via microwave-assisted Stille polymerization aiming at higher molecular weights for the final polymers.Their UV-vis properties,electrochemical properties and photovoltaic performances were investigated and discussed.Through the UV-vis spectras,we can clearly find that all of the three polymers have two similar absorption bands.After analyzing the UV-vis absorption spectra in solutions and thin films,it's clear that the maximum absorption peak of polymer PDPMIDSe-1 is redshift,which means that there is intensive ?-? stacking in solid state for this polymer.The cyclic voltammetry(CV)reveals that the HOMO levels of PDPMIDSe-1 PDPMIDSe-2 and PDPMIDSe-3 are-5.48 eV,-5.37 eV and-5.36 eV,respectively,which means that the introduction of thiophenes increases the energy levels of the polymers.The final device fabrication revealed the PDPMIDSe-2 possessed the best performance of power conversion efficiency(PCE)of 5.46%(Voc= 0.68 V,Jsc=12.23 mA/cm,FF = 0.65)among these polymers.The present results demonstrate that DPMIDSe is a potential candidate for donor unit of efficient polymer solar cells.