Synthesis And Photovoltaic Properties Of ADA’DA Small Molecule Acceptors With Non-fully-fused Core Units

Unfused-ring small molecule acceptors have a broad development prospect in the field of organic solar cells due to their simple synthesis and low cost.In this paper,we have designed and synthesized ADA’DA small molecule acceptor materials with non-fully-fused core units based on different electron-donating units.The optical properties,electrochemical properties and photovoltaic properties of the materials were systematically studied.（1）The cyclopentylthiophene（CPDT）unit is an ideal unit for the construction of acceptor materials because of its strong electron-donating ability.In order to enhance the intramolecular charge transfer,unfused-ring acceptors（C6,C7 and C8）were designed and synthesized by introducing strongelectron-withdrawingunitof dithieno[3’,2’:3,4;2’’,3’’:5,6]benzo[1,2-c][1,2,5]thiadiazole（DTBT）and5H-dithieno[3,2-b:2’,3’-d]pyran-5-one（DTP）with good planarity.TGA results show that C6,C7 and C8 have good thermal stability,which can meet the requirements of device preparation.UV absorption spectrum shows that the acceptor materials have strong light-absorption in the 500-800 nm region,which is beneficial to obtain higher J_sc.The LUMO energy level of C6 is higher than that of C7 and C8 by cyclic voltammetry and DFT calculation,which makes C6 have higher V_oc.Finally,when blending with a wide-bandgap polymer donor L1,C6,C7 and C8 delivered decent PCEs of 12.00%and11.92%,respectively,in organic solar cells.（2）The fully fused structure of indaceno[1,2-b:5,6-b’]dithiophene（IDT）is beneficial for efficient intramolecular charge transfer and face-on molecular arrangement.The ADA’DA acceptors IDTBT-4F and IDTP-4F with non-fully-fused core units were designed and synthesized based on this unit.The molecules present a banana-shaped backbone and have good planarity,which gives the two acceptors high electron mobility.UV absorption spectrum shows that the acceptor materials have strong light-absorption in the 540-800nm region,which is beneficial to obtain higher J_sc.The LUMO energy level of IDTBT-4F is higher than that of IDTP-4F by cyclic voltammetry and DFT calculation,which makes IDTBT-4F have higher V_oc.Finally,by optimizing the device,L1-S:IDTBT-4F and L1-S:ITDP-4F cells achieved photoelectric conversion efficiency of 12.00%and 11.92%,and high V_oc of 0.974V and0.945V,respectively.Therefore,ADA’DA small molecule acceptors with non-fully-fused core units provide a new design idea for the development of solar cell acceptor materials.