The Design,Synthesis And Device Characterization Of Small-molecule Donor Materials Based On Benzo[1,2-b:4,5-b’]dithiophene As The Core

Organic small molecules(SMs)possess some unique advantages including easy purification,well-defined molecular weight and easier energy level control,so small-molecule organic solar cells(SM-OSCs)have attracted more and more attention.To further improve the power conversion efficiency(PCE),in this paper,we designed and synthesized three A-D-A-type SM donor materials based on benzo[1,2-b:4,5-b’]dithiophene(BDT)as the electron-donating core,and fabricated the fullerene and non-fullerene SM-OSCs.We carried out the researches based on the relationship between the blend morphology in active layer and the photovoltaic performance,and designs of material and optimization of the devices were adopted to enhance the device performance.The main research contents are as follows:1.A SM donor BTTR based on thienyl-substituted BDT(BDT-T)as electron-donating core,thieno[3,2-b]thiophene(TT)along with two thiophenes as π-bridge,and 3-ethylrhodanine as end group was designed and synthesized.BTTR exhibited the optical bandgap of 1.78 e V,a deep-lying HOMO energy level of-5.32 e V and a relatively high hole mobility of 1.01×10-3 cm2 V-1 s-1.The SM-OSCs based on BTTR:PC71BM(1:0.8,w/w)with tetrahydrofuran solvent vapor annealing(SVA)exhibited an optimized PCE of 8.0% under the illumination of AM 1.5G,100 m W cm-2.2.A SM donor BTTz R based on BDT-T as electron-donating core,thiazolo[5,4-d]thiazole(TTz)along with two thiophenes as π-bridge,and 3-ethylrhodanine as end group was designed and synthesized.BTTz R showed strong absorption in the range of 300-700 nm,deep-lying HOMO energy level of-5.46 e V and suitable hole mobility of 1.60×10-3 cm2 V-1 s-1.The SM-OSCs based on BTTz R:IT-4F(1:1,w/w)with halogen-free carbon disulfide SVA exhibited an optimized PCE of 10.59% under the illumination of AM 1.5G,100 m W cm-2.This PCE of 10.59% is one of the highest values reported to date for the non-fullerene SM-OSCs.3.A SM donor BBDDR based on BDT-T as electron-donating core,benzo[1,2-c:4,5-c’]dithiophene-4,8-dione(BDD)along with two thiophenes as π-bridge,and 3-ethylrhodanine as end group was designed and synthesized.BBDDR exhibited the optical bandgap of 1.79 e V,a deep-lying HOMO energy level of-5.40 e V and high hole mobility of 1.14×10-3 cm2 V-1 s-1.The SM-OSCs based on BBDDR:IDIC(1:1,w/w)with chloroform SVA exhibited an optimized PCE of 7.82% under the illumination of AM 1.5G,100 m W cm-2.This was firstly applying the BDD in the non-fullerene SM-OSCs.