Synthesis And Photovoltaic Performance Of Small Molecule Acceptors Based On Benzothiadiazole And Bay-annulated Indigo

After decades of development,organic solar cells(OSCs)have been continuously explored by many researchers,their cell structure has been continuously developed and cell preparation technology has become more sophisticated.More importantly,the active layer materials and electrode buffer layer materials of OSCs have been greatly developed.At present,the power conversion efficiency(PCE)of OSCs has exceeded 17%,making it closer to large-scale industrialization.Therefore,we should continue to increase the research efforts of OSCs new materials in order to reduce the environmental pollution problems of traditional energy sources and solve some of the energy crisis,so as to maximize the use of solar energy for the benefit of the world.In this paper,two new series of small molecule acceptor materials(SMAs)were studied.Firstly,we synthesized nine aza-fused ring SMAs based on benzothiadiazole(BT)and benzodithiophene(BDT),the performance of SMAs with modified difference end groups and the introduction of thiophene ?-bridges was discussed.Secondly,two SMAs based on bay-annulated indigo(BAI)were synthesized,and the photovoltaic performance of SMAs with electron-drawing groups BAI as the core was discussed.The main research contents are as follows:(1)Four new benzothiadiazole-based small molecule acceptors X94 FIC,X9IC,X9 Rd,and X9T4 FIC were synthesized,they were modified with three different end groups under the same nine fused-ring structure,or a thiophene ?-bridge was introduced between the fused ring and the end group.Under the principle of energy level matching and complementary absorption spectra,polymer donor PBDB-T was selected to prepare OPV devices with four SMAs,respectively.Finally,under the optimal conditions of donor to acceptor mass ratio of 1:1 and active layer materials solution concentration of 14 mg/m L,the PCE of the OSCs based on X94 FIC,X9IC,X9 Rd and X9T4 FIC were 7.08%,6.29%,2.48% and 3.22%,respectively.It can be seen that the nine fused-ring small molecule acceptor with the terminal group 2FIC obtained the highest PCE.(2)Two new SMAs BAI-IC and BAI-Rd based on bay-annulated indigo were synthesized,BAI possess a highly planar molecular structure and excellent electron transport properties.Compared with BAI-Rd,BAI-IC exhibited a red shift in films,and BAI-IC had a wide spectral absorption range at 600-1000 nm.To test their photovoltaic performance,polymer donor materials PBDB-T and J71 were selected to prepare OPV devices with two SMAs,respectively.The highest efficiency of 0.51% was from PBDB-T: BAI-IC OPV devices.The reasons for the poor PCE of the two SMAs are mainly caused by the excessive aggregation of small molecules and the excitons cannot be effectively dissociated.In a word,two series of small molecule acceptors were synthesized.In addition,their photophysical,electrochemical and photovoltaic performances were studied.The results demonstrated that among some small molecule acceptors would possess the potential to become excellent organic solar cell materials.At the same time,we made some explorative contributions for the development of OSCs.