Synthesis And Optoelectronic Properties Of Small-molecule Acceptor Materials Based On Indacenodithiophene

Solar energy is recognized as a clean,pollution-free,inexhaustible and green sustainable energy source.Efficiently converting solar energy into electrical energy,thermal energy and other energy sources is one of the hot topics in the field of new energy and new materials.In recent years,polymer solar cells?PSCs?based on new non-fullerene small molecule acceptor materials have made rapid progress in device performance.At present,the energy conversion efficiency?PCE?of this type of solar cells has reached more than 18%.Through summarizing the literatures,in view of classical and efficient A-D-A small-molecule acceptor?SMAs?,a series of novel symmetry A-?-D-?-A and asymmetric A-D-?-A indacenodithiophene?IDT?-containing SMAs were designed and synthesized by introducing the?-conjugated bridges.The effects of different?-conjugated bridges and molecular symmetry on the molecular structures,photophysical properties,electrochemical properties and device performance of the target SMAs were studied in detail.The main research content is as follows:1. A series of A-?-D-?-A SMA materials?IDT-Py-IC,IDT-Fu-IC,IDT-Th-IC,and IDT-Ph-IC?were designed and developed with the good planarity and electron-rich indacenodithiophene?IDT?as a center electron-donating unit?D?,dicyanindene?IC?as the terminal acceptor unit?A?,and different aromatic rings?pyrrole,furan,thiophene and benzene?as?-conjugated bridges.The effects of different aromatic?-conjugated bridges on the molecular structures,photophysical,electrochemical and charge transport properties,as well as photovoltaic performance of the resultant SMAs were systematically studied.The results showed that these SMAs have good thermal stability,a wide absorption range?500?900 nm?and a high-lying LUMO energy level?-3.88?-3.67 e V?.Bulk heterojunction PSCs based on these SMAs were fabricated with a medium bandgap polymer PBDB-T as donor material.After optimization of device performance,the PSCs based on IDT-Th-IC exhibited the highest PCE of 8.72%.In constrast,the other three SMA materials of IDT-Fu-IC,IDT-Ph-IC,and IDT-Py-IC showed a PCE of 5.30%,4.28%,and 1.64%,respectively.2. A series of A-?-D-?-A SMA materials IDT-4OT-IC and IDT-8OT-IC were developed with the IDT as the central D unit,the IC as the terminal A unit,and electron-rich 3,4-dibutoxylthiophenes and 3,4-dioctyloxythiophene as the?-conjugated bridge,respectively.The effects of the length of alkoxy chain on the?-conjugated bridges on the photophysical,electrochemical properties and device performance of SMAs were systematically studied.The results showed that IDT-4OT-IC and IDT-8OT-IC have a similar absorption range?600?850 nm?to the methoxyl substituted IDT-OT-IC in solution.There are obvious absorption shoulders in the film state,and IDT-OT-IC and IDT-4OT-IC displayed a significant red-shift absorption spectrum compared to IDT-OT-IC.With the increase of the number of carbon atoms in the alkoxy chain on the thiophene bridge,the solubility of these SMAs is improved and the HOMO energy level is decreased.PBDB-T was selected as the donor material to pair with these SMAs to prepare PSC devices.Preliminary results showed that IDT-4OT-IC and IDT-8OT-IC produced a PCE of 1.60%and 1.19%,respectively.3. A new symmetric A-?-D-?-A SMA IDTV-2Et and asymmetric A-?-D-A SMA IDTV-Et were designed and developed with aromatic methylene substituted IDT?IDTV?as the central D unit,electron-withdrawing ethyl-3-thienylacetate group as the?-conjugated bridge,and IC as the terminal A unit.The effect of electron-withdrawing?-conjugated bridge?ethyl-3-thienylacetate?on the photophysical,electrochemical properties and photovoltaic performance of SMAs was systematically studied.The results showed that IDTV-Et and IDTV-2Et with electron withdrawing?-conjugated bridge have a wider absorption spectrum and a lower optical bandgap(E_g^opt)than that of IDTV-Ph without?-conjugated bridge.Because the two SMAs contain different numbers of ethyl-3-thienylacetate bridges,the synergistic effect of the ester group and the terminal IC is also different,which leads to the decrease of LUMO energy levels of the resultant SMAs.Using PBDB-T as donor material and these SMAs as acceptor material,bulk heterojunction PSCs were fabricated.Preliminary results showed that the PCE of IDTV-2Et-and IDTV-Et-based devices is 1.11%and 2.98%,respectively.