Synthesis And Photovoltaic Performance Of Non-fullerene Acceptors Based On Thiophene-substituted Dicyanoindanone

Polymer solar cells?PSCs?have been rapidly developed in recent years.The A-D-A-type non-fullerene acceptor materials,which consist of a strong electron-donating unit?D?as core and two electron-withdrawing units?A?as arms,have achieved a breakthrough,and the highest photoelectric conversion efficiency?PCE?values of the PSCs have far exceeded those of the PSCs based on fullerene derivatives.To exploit new A-D-A acceptor materials,scientific researchers generally adopt the following strategies,such as exploiting new electron-donating units,exploiting new electron-withdrawing units and optimizing side chains.Accordingly,a new electron-withdrawing unit,2'-bromothiophene-substituted 3-dicyan-1-indanone?SDCN-Br?has been designed and synthesized,then an A-D-A small molecular acceptor based on SDCN-Br and indacenodithieno[3,2-b]thiophene derivative?IDTT?and a polymeric acceptor based on SDCN-Br and indacenodithiophene derivative?IDT?.Moreover,their thermal stability,photophysical properties,electrochemical properties and photovoltaic performance have been studied.1.2'-Bromothiophene-substituted 3-dicyan-1-indanone?SDCN-Br?has been designed and synthesized in order to use as the terminal electron-withdrawing units?A?,then the A-D-A small molecular acceptor,named as ITC-2Br,was synthesized by Knoevenagel condensation reaction between IDTT derivative and SDCN-Br.The acceptor ITC-2Br has strong light-harvesting capacity in the band between 500 nm and 800 nm.Compared with the analogous acceptor without bromine atoms,ITC-2Br presents a red-shifted absorption spectrum and the lower band gap,so the short-circuit current density(J_sc)of the PSC based on PBDB-T:ITC-2Br blend film increases to18.53 m A cm^-2.However,the introduction of bromine atoms in ITC-2Br leads to a low-lying LUMO?lowest unoccupied molecular orbital?energy level,which results in a smaller open-circuit voltage(V_oc)of 0.86 V in its PSC based on PBDB-T:ITC-2Br.In addition,the morphology of the PBDB-T:ITC-2Br blend film was not further optimized,so the fill factor is only 54.38%and the PCE is only 8.53%.Compared with PBDB-T,PM6 possesses better spectral complementarity with ITC-2Br,so the PSC based on PM6:ITC-2Br shows better photovoltaic performance with a PCE of9.98%.The small molecular acceptor ITC-T was obtained by substituting thiophene for bromine,which presents a slightly redshifted absorption spectrum and higher-lying LUMO energy level.The PSC devices were prepared with PBDB-T as the donor and ITC-T as the acceptor,which showed a V_ocof 0.92 V,a J_scof 8.32 m A cm^-2,a FF of 41.43%,and a PCE of 3.16%.The photovoltaic performance is significantly lower than that of the PSC based on ITC-2Br as the acceptor.It is inferred that the poor solubility of ITC-T in the solvents would result in an inferior compatibility with the donors,which limits exciton dissociation and carrier transport,so the PSC showed low J_sc,FF and PCE values.2.The monomer IDT-C16-2Br was synthesized by Knoevenagel condensation reaction using SDCN-Br and IDT derivative with cetyl side chains as the reactants,the it was copolymerized with 2,5-bis?trimethylstannyl?thiophene through a Stille coupling reaction to obtain polymer PH1.The results show that the polymer PH1exhibits good thermal stability and strong absorption in the band between 500 nm and800 nm.The all-polymer solar cells have been prepared with PBDB-T as the donor material and PH1 as the acceptor material.When no additive is used to prepare the photoactive layer,the blend film shows poor morphology with large domain size,which results in a suppressed exciton separation,inferior charge transport as well as serious charge recombination,so the J_scand FF values of the PSC are low and the PCE is only 1.94%.When 4%chloronaphthalene is added as an additive to prepare the photoactive layer,the blend film presents better morphology with small domain size,which leads to more efficient exciton separation,better charge transport as well as less charge recombination,so the J_scand FF values of the PSC are greatly increased and the PCE is improved to 6.34%.