Synthesis And Characterization Of D-A Copolymer Donor Materials

Nowadays organic solar cells(OSCs)have attracted great attention due to the advantages of light weight,low energy consumption,rich selection of raw materials,solution processing,straightforward fabrication and flexibility to fabricate large-area devices.In recent years,benefitted from the rapid development of non-fullerene acceptor materials(NFAs),the device efficiency of OSCs have boosted remarkably.In order to further improve the photovoltaic performance of OSCs,it is significant to design and synthesize new donors for matching with the narrow-bandgap acceptors.D-A-type copolymer donors have attracted great attention due to the advantages of easy adjustment of molecular structure,energy level and bandgap.On this basis,in this thesis three series of new D-A copolymer donors were designed and synthesized,and their thermal stability,optical absorption,molecular energy levels,morphology of blend films as well as the photovoltaic performance were investigated.The main research contents of this thesis are as follows:(1)Two new D-A copolymer donors PL1 and PL2 that possessed acceptor units with corresponding asymmetric structure and symmetrical structure are designed and synthesized,by copolymerizing pyrrole ring contained ester group on the side chain of benzothiadiazole(BT)unit and benzodithiophene(BDT)unit contained thiophene thioalkyl side chain.After studying the test results,it founded that these two donors both have good thermal stability and,PL2 has stronger photo-absorption property in the long wavelength range and deeper HOMO energy level,compared with PL1.(2)Three new wide-bandgap copolymer donors PD1,PD2 and PD3 are synthesized by copolymerizing dithieno[3,2 f:2’,3’-h]phthalimide unit with thiophene unit,thieno[3,2-b]thiophene unit and 3,4-difluorothiophene unit,respectively.And then,we systematacially investigated the effect of different thiophene units on optical and electrochemical properties of polymer donors.By comparing with PD1,we found that PD2 exhibited red-shifted absorption spectrum and up-shifted HOMO,and the HOMO energy level of PD3 was deeper.(3)Three new bridge-type copolymer donors D20,D21 and D22 that based on BDT unit and dithieno[3,2 f:2’,3’-h]phthalimide unit were designed and synthesized.We systematically studied the effects of different conjugated side chains on the thermal stability,optical absorption and molecular energy levels of three donor materials.The results indiated that all three donors showed good thermal stability,and D20 possessed deepest HOMO energy level due to the electron-accepting property of F atom.The OSCs devices based on D20,D21 and D22 gained PCE of 3.06%,8.63%and 4.66%,respectively,when combined with Y6 as the acceptor.