Synthesis And Photovoltaic Properties Of The Donor Materials Constructed With P-difluorobenzene Derivative As Well As S-tetrazine Derivative

Polymer solar cells（PSCs）have been paid plentiful attention owing to the underlying application in lightweight,flexible,and large-area devices.Electron donor materials play an important role in absorbing light,transferring excitons and transporting holes as one of the key components of PSCs.In this dissertation,a p-difluorobenzene-based small-molecular donor and two s-tetrazine-based terpolymers were designed and synthesized,and the effects of these electron-withdrawing units on light absorption,energy levels,morphology,exciton dissociation and charge transfer of the donors have been studied in detail.1.A new small-molecular donor,BTBR-2F,based on a benzo[1,2-b:4,5-b′]dithiophene（BDT）derivative as an electrondonating core,two octylthiophene-2,5-difluorobenzene-octylthiophene units asπbridges and two 3-ethylrhodanine units as electron-withdrawing terminal groups was designed and synthesized in order to achieve more complementary absorption with a PM6:Y6 blend in the near-ultraviolet region.Moreover,BTBR-2F possesses lower the highest occupied molecular orbital（HOMO）and the lowest unoccupied molecular orbital（LUMO）energy levels than PM6,which leads to more efficient energy/charge transfer and higher open-circuit voltage(V_OC)in ternary PSCs.The ternary blend film with 20%BTBR-2F achieves the best morphology with a nanofibrous network structure and small domain size,which results in the most efficient exciton dissociation,highest charge mobilities,and lowest charge recombination.Therefore,the ternary device with 20%BTBR-2F achieves the highest efficiency of 17.38%,with a V_OC of 0.859 V,short-circuit current density(J_SC)of 27.30m A cm^-2,and fill factor（FF）of 74.11%,which are comprehensively better than the photovoltaic parameters of the corresponding binary PSCs based on PM6:Y6 blend(PCE=15.31%,V_OC=0.831 V,J_SC=26.30 m A cm^-2,FF=70.05%).The study presents an efficient noncovalent conformational locking strategy to tune the energy levels,absorption band and molecular aggregation of a small molecular donor for high-performance ternary organic solar cells.2.Two terpolymers,TP-H and TP-EH,have been designed and synthesized by incorporating hexyl-or 2-ethylhexyl-substituted 3,6-bis（4-alkylthiophen-2-yl）-1,2,4,5-tetrazine derivatives as the second electron-withdrawing moieties with a 20%molar ratio into the backbone of PM6,respectively.The introduction of s-tetrazine units can efficiently depress the HOMO energy levels of the terpolymers,which results in higher V_OC values than those of the PSCs based on PM6:Y6.TP-H with hexyl side chains possesses a stronger molecular aggregation than TP-EH with 2-ethylhexyl side chains,and the former also shows better morphology with a nanofibrous network structure than the latter in blends with the acceptor Y6,which are all favorable for charge transport and exciton dissociation.As a result,the OSC based on the TP-H:Y6 blend achieves a higher efficiency of 16.76%with a J_SC of 26.78 m A cm_-2,a V_OC of 0.851 V,and a FF of73.53%,while the PSCs based on PM6:Y6 only presents a lower PCE of 15.32%(V_OC=0.826 V,J_SC=26.57 m A cm^-2,FF=69.82%).This work provides not only two s-tetrazine-based terpolymers for high-performance PSCs but also some insights in design strategy and side-chain engineering for terpolymers.