Design,Synthesis And Photovoltaic Property Research Of High-Efficiency Organic Small Molecule Donors

Organic solar cells(OSCs)have attracted extensive attention in related fields because of their advantages of low cost,light weight,flexible,and solution processing.All-small-molecule(ASM)organic solar cells based on small molecule donor/acceptor have great application prospects because of the advantages of clear molecular structure,easy modification,a small batch difference of materials,and high repeatability of devices.How to improve the properties of small molecule materials through molecular chemical structure design,and then optimizing the phase separation morphology of the active layer is the key to improving the performances of ASM OSCs.In this thesis,based on the molecular design strategy of side-chain engineering,several novel high-efficiency organic small molecule donor materials were designed and synthesis.And then,we systematically explored the structure-activity relationship between molecular structure design and the basic photoelectric properties of small molecule donors and the overall performance of ASM OSCs,to provide reasonable and effective design ideas for the development of small molecule donor materials.Firstly,the fused-aromatic-ring unit benzothiophene(BT),as the two-dimensional conjugated side-chain,was attached to the benzo[1,2-b:4,5-b']-dithiophene(BDT)core to expand the conjugated skeleton of the whole molecule.And a new small molecule donor material,named BTR-BT,was synthesized.The results reveal that the expansion of the conjugated system by fused-aromatic-ring side-chain enhanced the molecular ?? stacking,improved the molecular crystallinity,effectively regulated the phase separation morphology of the active layer.In addition,the interpenetrating network structure with appropriate size was formed in the blend film,and achieved a relatively excellent balance between exciton dissociation and charge transmission.BTR-BT:Y6based ASM OSCs possess higher charge transport efficiency,less carrier recombination,longer carrier lifetime,and faster carrier extraction;as a result,BTR-BT:Y6-based ASM OSCs achieved the power conversion efficiency(PCE)of 13.63%.Secondly,two novel small molecule donors,named C-F and C-2F,were designed and synthesized,both of which have fluorinated phenyl conjugated side-chain,and the difference is that they have different substitution numbers of fluorine atoms.C-F-based and C-2F-based ASM OSCs' PCE were 7.76%and 14.64%,respectively.The research shows that the high PCE of C-2F with symmetrically difluorinated phenyl group conjugated side-chain may be due to:The effect of drawing molecular energy level with bifluoride atoms is more obvious,which can better match the acceptor energy level.Moreover,symmetrically difluorinated phenyl group conjugated side-chain is beneficial to stabilize molecular conformation,enhance ?-? stacking and change molecular crystallization performance,and then enhance the performances of ASM OSCs from the perspective of improving the phase morphology and crystallinity of the active layer blend.As a reasonable and effective molecular design strategy,side-chain engineering provides a new solution to the problem that the morphology of small molecule donor/acceptor active layer blend is difficult to control,and has positive significance for further improving the performances of ASM OSCs.