Design and synthesis of 2D A1-π-A2 copolymers impact on fullerene network for efficient polymer solar cells

Abstract

A new building block of two-dimensional (2D) A1-π-A2 copolymers for P(dDTPz-ID) and P(dDTPz-DTBT) was designed and synthesized. Their structures have two strong acceptor units (isoindigo and benzothiadiazole derivatives) in the backbone, respectively. It displayed a benefit of A1-A2 building blocks, which is complementary and broad light absorption from 300 to 750 nm due to acceptors with different withdrawing strengths. Also, the introduction of dangling-thiophene, π unit allowed the formation of 2D-strcuture, which and led to effective and inter-chain packing of PC71BM for both copolymers. Two copolymers exhibited enhanced π-π stacking properties and had predominant face-on structure, which was confirmed by XRD. We also reviewed the optical, electrochemical, morphological, charge transport properties and performance compared with A1-A2 copolymers for P(DTPz-ID) and P(DTPz-DTBT), respectively. The inverted device fabricated with optimized condition for P(dDTPz-DTBT) showed efficient charge transport from enhanced energy alignment, high Voc and dipole moment and fine morphology, and thus obtained 5.0% of best power conversion efficiency (PCE).