Synthesis And Application Of Fused-Ring Small Molecule Non-Fullerene Electron Acceptor Materials

Organic solar cells or organic photovoltaics(OPVs)have attracted much attention because of the advantages such as low cost,flexibility,roll-to-roll printing,light weight.In recent years,under the persistent efforts of scientists,it has made great progress in the research of OPVs.Currently,the power conversion efficiency(PCE)of the single junction based OPVs have achieved above 16%,and the power conversion efficiency of tandem solar cells have reached over 17%.It demonstrated that OPVs have potential for industrialization in the future.So,it is important to explore more efficient and available active-layer-materials.Nowadays,many works have reported the A-D-A type non-fullerene electron acceptors which enriched the electron acceptor materials,enlarged the selectivity for electron acceptor materials and expedited the power conversion efficiency for OPVs.This research work are divided into three parts to modify the non-fullerene electron acceptors.They are modification on the fused-ring central building block,side chain engineering and modification on the terminal group.The first part is to modify the fused-ring central building block.Based on the IDT core in the short-axis substitution we introduced methyl substitution on central benzene position,so the new pentacyclic ladder-type arene IDMe was designed and synthesized.And then we got non-fullerenes materials IDMe-IC.Compared with the IDIC materials,the active layer based on PBDB-T:IDMe-IC shows red-shifted absorption spectrum,narrow optical band gap;and the materials IDMe-IC shows better crystallinity and stronger molar absorption coefficient.Therefore,the value of PCE is 30%higher than that of PBDB-T:IDIC based polymer solar cells(6.46%)and also get higher short-circuit current(14.13 mA cm-2).The second part is on side chain engineering.Based on the IDTIDT backbone with a doubled IDT as the core,a new non-fullerene with m-IDTIDT as the core was obtained by changing the para-alkyl-phenyl side chain for meta-alkyl-phenyl.Compared with p-IDTIDT-IC,m-IDTIDT-FIC has smaller π-π distance,larger crystalline coherence length and a higher electron mobility.The polymer solar cell based on J71:m-IDTIDT-FIC achieved the best photovoltaic performance with a PCE of 11.32%.The final part is to modify the terminal group.Two new non-fullerene acceptor materials BT-SFIC and BT-FIC were designed and synthesized by modifying the terminal group IC units with fluorinated.Due to the strong electron-withdrawing ability of the fluorine atoms,the materials BT-SFIC and BT-FIC have narrow band gap absorptions and their absorption peak edges reach 900 nm in the near-infrared region.Their energy levels and absorption spectra are matched with the polymer donor material PTB7-Th.Thus,the polymer solar cells based on PTB7-Th:BT-SIC and PTB7-Th:BT-FIC achieved the PCEs of 9.52%and 10.10%,respectively.