Synthesis,Characterization And Photovoltaic Performance Of Non-fused Ring Framework Brominated Small Molecule Acceptor And Random Copolymer Donor

In recent years,organic solar cells(OSCs)have developed rapidly and have attracted attention because they can be made into large-area,light-weight,flexible and translucent devices through solution processing.The photoactive layer of an organic solar cell is composed of a blended film of donor and acceptor materials.Broad visible-NIR absorption,higher charge carrier mobility,and suitable electronic energy levels of both the donor and acceptor materials are crucial for high-efficiency OSCs,Therefore,matching suitable acceptor and donor materials is a key issue to improve the performance of organic solar cells.Non-fullerene OSCs have experienced a rapid increase in efficiency,benefiting from the development of small-molecule acceptors(SMAs).The widely studied SMAs for high-performance OSCs mostly contain a generally large fused-ring core and fluorination of the end group.In this thesis,two brominated small molecule acceptors with simple non-fused frameworks were designed and synthesized,and they were blended with the donor PM6 to prepare devices.At the same time,this paper also synthesized a series of(D-A)_m-(D-D1)_n-type random polymers.Through the optimization of the device preparation process,it is expected to obtain high-efficiency organic solar cells.The specific work is summarized as follows:1.Two brominated small molecule acceptors with simple non-fused frameworks were synthesized by Suzuki coupling reaction,named F8IDT-Br and C8IDT-Br,in which the fluorene or carbazole ring acts as an electron-donating central core(D)by employing thiophene as the?bridge and brominated 1,1-dicyanomethylene-3-indanone as the end group(A).Optical,electrochemical,and thermal properties and crystalline behaviors of these two acceptors were characterized.The two acceptors are directly compared to explore the effects of the core moiety on the intrinsic and photovoltaic properties.The widely used polymer PM6 was selected as a donor to fabricate the devices.As a result,a power conversion efficiency(PCE)value of 9.70%is obtained in PM6/F8IDT-Br-based devices,outperforming the previously reported results(PCE:<8%)from OSCs based on non-fused fluorene core-based acceptors.It means that bromination of non-fused SMAs can further improve relevant device performance.The best PCE value of 9.85%is achieved in PM6/C8IDT-Br-based devices,which is noticeable efficiency in non-fused SMA-based OSCs.Moreover,the devices based on these two brominated acceptors exhibit excellent storage stability.The results demonstrate that these two acceptors are excellent materials among simple non-fused SMAs.2.A class of(D-A)_m-(D-D1)_n random polymers based on benzodithiophene units and thienothiophene dione units was designed and synthesized by Stille coupling polycondensation reaction.The polymers were characterized by GPC,elemental analysis,UV-Vis,CV.The results show that the molecular weights of these polymers are in line with the basic conditions for preparing devices,and they have good solubility in both chloroform and chlorobenzene.At the same time,as the proportion of the third component increases,the ultraviolet absorption of the polymer has a slight blue shift,which indicates that the use of PM6-T series polymer with Y6 can collect more photon energy in the solar spectrum.A good complementary absorption is formed,so it is beneficial to increase the short-circuit current density of the device.CV results show that as the proportion of the third component increases,the HOMO and LUMO energy levels of the polymer increase,so the electrochemical band gap of the polymer increases significantly,which may lead to higher V_OC.Then,these polymers were used as donor materials and Y6 was used as acceptor materials to prepare devices.The device structure is ITO/PEDOT:PSS/Active layer/PDINN/Ag.The influence of these factors on the performance of the device was discussed in terms of active layer spin coating speed,D/A mass ratio,annealing time,solvent additives,etc.,and the best conditions for device preparation were obtained.The PCE of the optimized device is 14.51%,14.17%,15.76%,16.64%and 13.94%,respectively.Using external quantum efficiency analysis(EQE)to study the optical response performance of the device.The results show that the active layer of PM6-T15/Y6 is the device with the highest PCE in this system,which is higher than the previously reported PM6/Y6 device,indicating that the random copolymerization method can improve the performance of the device,this provides a new idea for the preparation of high-efficiency OSCs in the future.