Gradual chlorination at different positions of D-π-A copolymers based on benzodithiophene and isoindigo for organic solar cells

摘要

Isoindigo(IID)has been widely used as strong acceptor unit(A)to construct narrow bandgap polymers in organic field effect transistors(OFETs)and organic solar cells(OSCs).Combing with IID,we chose benzodithiophene(BDT)as the donor unit(D)and thieno[3,2-b]thiophene(TT)as theπbridge to construct a new type of D-π-A polymer PE70.Based on PE70,we adopt the chlorination strategy to fine-tune photoelectric characteristics and film morphology,and then developed PE74 and PE75.By blending with non-fullerene acceptor(NFA)Y6,device based on PE74 with chloride substitution on the BDT unit showed increasing photovoltaic performance.In addition,further chlorine substitution on the IID(PE75)would greatly reduce the non-radiative voltage loss(ΔV3),and the distorted molecular conformation also took responsible for the excessive recombination.As results,PE74:Y6-based device achieves a power conversion efficiency(PCE)of 11.06%with open-circuit voltage(VOC)of 0.76 V,which are higher than those of PE70:Y6(PCE of 10.40%and VOC of 0.72 V)and PE75:Y6-based device(PCE of 6.24%and VOC of 0.84 V).This work demonstrates the regularity of the photovoltaic performance caused by chlorination strategy in polymer in the non-fullerene OSC devices,which provide important insights into highperformance photovoltaic materials.