The Design,Synthesis And Device Performance Characterization Of Non-Fullerene Small Molecule Electron Acceptor Photovoltaic Materials

In last several years,organic solar cells(OSCs)have attracted considerable attention of researchers due to their unparalleled advantages of flexibility,light weight,semitransparent.and low cost.As the main unit of photo-electric conversion,the continuous update of active layer materials has always been the foremost driving force for the power conversion efficiency(PCE)improvement of OSCs.The recent rapid development of non-fullerene small molecule acceptor(NF-SMA)materials has promoted a significant increase in PCE of OSCs.In this thesis,we have designed and synthesized two NF-SMA systems.We use different molecular structure design strategies to adjust the absorption spectrum,molecular energy level and aggregation characteristics of these materials.Besides,we have systematically researched the relationship between photovoltaic performance and molecular structure based on these two NF-SMA material systems.The main research contents and results are as follows:1.A novel NF-SMA(NTO-4F),containing a alkoxy-substituted naphtho[1,2-b:5,6-b’]dithiophene as central core and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1 H-inden-1-ylidene)malo nonitrile(IC-2F)as electron-withdrawing end groups,was designed and synthesized.The effect of conjugated central core and side chain oxygen atoms on the properties of NTO-4F was studied.NTO-4F exhibits a strong absorption in the region of 550-800 nm and a high LUMO energy level(-3.88 eV).In combination with the wide bandgap polymer donor,PM6,the optimized device achieved a PCE of 11.5%with a high Voc of 0.99 V.Moreover,the PM6:NTO-4F-based device exhibited excellent thermal stability.2.By introducing a simple thioalkyl-substituted thiophene as a unilateral asymmetricπ bridge and using its non-covalent bond interaction to construct an asymmetric non-covalent fused ring core,a novel NF-SMA namely IDTST-4F,was designed and synthesized.The effect of asymmetric π bridge on the absorption spectrum,molecular energy levels,charge transport,and device photovoltaic performance of small molecule acceptors was systematically investigated.Compared to the fused ring symmetric NF-SMA,IDT-4F,IDTST-4F exhibits a wider absorption spectrum,a higher LUMO energy level and a similar electron mobility.The optimized OSC based on PM6:IDTST-4F blend film exhibited a high PCE of 13.8%with a Voc of 0.87 V,a Jsc of 21.9 mA/cm2 and a FF of 0.72.On the contrary,the optimized OSC based on PM6:IDT-4F blend film only obtained a much lower PCE of 7.8%with a Voc of 0.83 V,a Jsc of 15.3 mA/cm2 and a FF of 0.62.