Triphenylamine side chain enabled polybenzodithiophene wide-bandgap donors for efficient organic solar cells

Abstract

A wide-bandgap two-dimensional polymer PBDT-BDT based on alternating benzo[1,2-b:4,5-b′]dithiophene (BDT) units with triphenylamine (TPA) conjugated side chains is designed and synthesized. Benefiting from the prolonged conjugation of the side groups, PBDT-BDT exhibits excellent light-harvesting properties ranging from 300 to 600 nm, especially including strong ultraviolet absorption due to the featured absorption of TPA groups, which is complementary to the absorption region of the well-known non-fullerene acceptor Y6. Additionally, PBDT-BDT shows a deep highest occupied molecular orbital energy level (−5.45 eV). When blended with the PC61BM acceptor, the PBDT-BDT-based device achieves a PCE of 6.33% with a high open-circuit voltage (V_oc) of 0.91 V, while the PBDT-BDT:Y6 device achieves a PCE of 12.26% with a short circuit current of 21.58 mA cm⁻² and a fill factor of 71% due to the efficient charge transport and a favorable active layer morphology. This work suggests that maintaining the donor–donor polymer backbone with the BDT unit forming suitable conjugated side chains is an effective two-dimensional strategy for obtaining highly efficient wide band-gap polymers for fullerene-based and fullerene-free OSCs.