New Wide Bandgap Conjugated D‐A Copolymers Based on BDT or NDT Donor Unit and Anthra1,2‐b:4,3,bʹ:6,7‐cʺtrithiophene‐8‐12‐dione Acceptor for Fullerene‐Free Polymer Solar Cells

摘要

Abstract Two donor–acceptor (D‐A) copolymers, P128 and P129, containing benzodithiophene (BDT) and naphthiodithiophene (NDT) donor unit, respectively, and the alike anthra[1,2‐b:4,3,bʹ:6,7‐cʺ] trithiophene‐8‐12‐dione(A3T) as an acceptor unit, are synthesized. The P129 (NDT donor) exhibits enhanced chain planarity and linearity of backbone compared to P128 (BDT donor), which leads to a considerable increase in both the light‐harvesting ability and hole mobility. In addition to it, the incorporation of the NDT unit creates a strong modification in the morphology with a well‐mixed interpenetrating nanofibrillar network with an increased donor–acceptor interface in the P129:Y6 bulk heterojunction active layer that leads to a high short‐circuit current density and fill factor. The power conversion efficiency (PCE) of the improved polymer solar cells based on P128:Y6 and P129:Y6 is 6.25% and 14.55%, respectively. The negative HOMO offset (−0.02 eV) at P128/Y6 interface restricts the hole transfer from Y6 to P128 and results in low value of short‐circuit current and thereby poor PCE. Finally, the ternary PSCs are constructed with a weight ratio of 0.5:0.5 between P128 and P129 and the weight component of Y6 is kept constant and the PSC attains a PCE of 16.19%. This increase in the PCE can be attributed to the formation of semiconducting alloy based on P128 and P129 donors and the transformation of HOMO offset from negative (−0.02 eV for Y6/P128) to positive (0.04 eV for Y6/P128:P129).