Synthesis And Study Of Novel DA Conjugated Polymer Donor Materials For Organic Solar Cells

Polymer solar cells(PSCs)have been viewed as a promising photovoltaics technology due to the merits of lightweight,flexibility,roll-to-roll fabrication and other advantages.In recent years,it has gained a rapid development and widespread concern.Using electron-donating(D)and electron-accepting(A)building blocks to construct D-A copolymers is the key toward high performance PSCs.The ideal D-A copolymers generally have a relatively small bandgap to harvest more photons,a deep HOMO level to generate a high open-circuit voltage(Voc),a good crystallinity to realize high hole mobility and a proper miscibility with the acceptors to make ideal nanoscale phase separation,thereby improving the PCE of the device.However,many high performance polymers for PSC applications have complicated structures.Arduous synthesis and expensive intermediates are frequently involved for obtaining small amount of materials.These difficulties may restrict or even prohibit the practical applications of these materials.Therefore,the development of new polymers for highly efficient PSCs and concise chemical structures is still a big challenge.Polycyclic aromatic lactams(PALs)have emerged as promising "A" units for D-A copolymers.The strong electron-withdrawing capability and the good planarity of PAL units endow D-A copolymers with deep HOMO levels and high hole mobilities.Dithieno[3,2-b:2’,3’-d]pyridin-5(4H)-one(DTP)has proved to be a good acceptor unit for developing efficient D-A copolymers.However,previous research focused on DTP copolymers with relatively wide bandgaps(Egopt>1.80 eV)and the performance of these copolymers in non-fullerene PSCs has not been investigated.To harvest more photons,it is essential to develop low-bandgap.Isoindigo comprises an electron-defi cient symmetrical lactam and aromatic groups.At the same time,the solubility of the molecules can also be adjusted by the side chains on the lactam N position.In addition,it has advantages of wide source,simple structure and synthesis.Therefore,isoindigo as an excellent A unit is widely used in D-A polymers of solar cell.In this paper,the D-A copolymer PDTP4TFBT,which is a novel donor based on tricyclic lactam(DTP)unit,was designed and synthesized.At the same time,the D-A copolymer donor materials PITTIBDT and PiITTIBDT were synthesized based on the novel isoindigo acceptor unit.We made a study of their optical properties,thermal stability,electrochemical property and photovoltaic performance.The main contents and results are as follows:(1)In this work,we developed a low-bandgap DTP copolymer(PDTP4TFBT)with a Egopt of 1.62 eV and applied it in both fullerene and non-fullerene solar cells.PDTP4TFBT as a donor material functioned well in both fullerene and non-fullerene solar cells,giving PCEs up to 8.75%and 7.58%,respectively.Moreover,We gaind a high performance ternary-blend solar cells based on PDTP4TFBT,fullerene and non-fullerene acceptors afforded a decent PCE of 9.20%.PDTP4TFBT,PC71BM and ITIC present complementary absorption and stepwise energy level alignments,suggesting that they may build up an efficient active layer.Finally,to understand the different effects of DIO on the performance of fullerene and nonfullerene solar cells,we studied the morphology of the active layers by atomic force microscope(AFM)and transmission electron microscope(TEM).To fiure out the molecular packing and orientation,we did grazing-incidence wide-angle X-ray scattering(GIWAXS).(2)(3Z,3’Z)-3,3’-(thieno[3,2-b]thiophene-2,5-diylbis(methanylylidene))bis(6-brom o-1-(2-octyldodecyl)indolin-2-one)(Ml)and its isomers(Z)-6-bromo-3-((5-(((Z)-6-bromo-2-((2-octyldodecyl)oxy)-3H-indol-3-ylidene)methyl)thieno[3,2-b]thiophen-2-yl)methylene)-1-(2-octyldodecyl)indolin-2-one were obtained by introducing thieno[3,2-b]thiophene between isoindigo.The co-planarity of skeleton,the molecular delocalization and the carrier mobility were improved due to the weak interaction of the O…S.We developed two wide-bandgap D-A polymer donor materials PITTIBDT and PiITTIBDT,using the novel isoindigo as electron-donating(D)and the benzodithiophene(BDT)as electron-accepting(A).PITTIBDT and PiITTIBDT were blended with the fullerene acceptor(PC71BM)give a PCE 3.99%and 2.59%,respectively.Finally,the optical,thermal stability,electrochemical and photovoltaic properties of the two isomer donor materials were compared.