Development And Application Of Small-molecule Acceptors Based On Benzodithiophene Units For Polymer Solar Cells

The rapid development of organic solar cells in recent years has made it possible for commercial applications.Among them,single-cell polymer solar cells?PSCs?have achieved great breakthroughs and more than 13%of power conversion efficiency?PCE?,thanks to the fact that many excellent photovoltaic materials,especially for nonfullerene acceptors,have been developed and optimized by people.A classical three-membered fused-ring compound,benzodithiophene?BDT?,has shown superior performance as a structural unit for the construction of organic photoelectric materials.In the research work of this dissertation,we developed a series of acceptor-donor-acceptor?a-d-a?type acceptors based on BDT units and focused on the effect of isomeric backbone,terminal group optimization and side chain modification,for further improving the performance of polymer organic solar cells.?1?A-d-a-type non-fullerene acceptor material BDT-IC containing BDT unit was designed and synthesized.BDT-IC with seven-membered fused-ring backbone BDCPDT that is isomeric with IT-IC,showed more red-shifted absorption spectrum and narrower energy gap.BDT-IC exhibited better carrier mobility thanks to its better crystallinity and tighter molecular packing in organic thin films.The PCE of 10.5%was obtained by BDT-IC based PSCs with polymer donor J71,which is higher than the PSCs based on IT-IC.?2?A novel BDT-based non-fullerene acceptor material,BT-CIC,was synthesized by the introduction of Cl atom on the terminal group.Due to the electron-withdrawing effect of Cl atoms,BT-CIC has an ultra-narrow band gap of E_g=1.33 eV,and the absorption edge reaches 930 nm in the near-infrared region.Besides,the Cl atom enhanced the stacking between molecules in the solid film and greatly increased J_SCof the device.The PCE of the device with the polymer donor J71 reached 11.2%.Furthermore,the PCE of 7.1%is achieved by semitransparent organic solar cell based on BT-CIC with average transmittance of 43%.?3?Two new acceptor materials CBT-IC and SBT-IC were synthesized by introducing n-hexyl and n-hexylthio on the BDT-based backbone,respectively.By comparison with BDT-IC,it was found that the different push/pull electronic properties of the side chains have a significant effect on the light absorption and molecular energy level of the acceptor materials.In addition,in the solid film,the introduction of n-hexyl and n-hexylthio weakened the crystallinity of the materials,but the balance of carrier mobility in the blend film with J71 was improved.Finally,the PCEs of 11.02%and11.28%were achieved in PSCs based on CBT-IC and SBT-IC,respectively,both higher than BDT-IC.