Comprehensive study of pyrido[3,4-b]pyrazine-based D-π-a copolymer for efficient polymer solar cells

Two D-π-A copolymers, based on the benzo[1,2-b:4,5-b′]-dithiophene (BDT) as a donor unit and benzo-quinoxaline (BQ) or pyrido-quinoxaline (PQ) analog as an acceptor (PBDT-TBQ and PBDT-TPQ), were designed and synthesized as a p-type material for bulk heterojunction (BHJ) photovoltaic cells. When compared with the PBDT-TBQ polymer, PBDT-TPQ exhibits stronger intramolecular charge transfer, showing a broad absorption coverage at the red region and narrower optical bandgap of 1.69 eV with a relatively low-lying HOMO energy level at -5.24 eV. The experimental data show that the exciton dissociation efficiency of PBDT-TPQ:PC₇₁BM blend is better than that in the PBDT-TBQ:PC₇₁BM blend, which can explain that the IPCE spectra of the PBDT-TPQ-based solar cell were higher than that of the PBDT-TBQ-based solar cell. The maximum efficiency of PBDT-TPQ-based device reaches 4.40% which is much higher than 2.45% of PBDT-TBQ, indicating that PQ unit is a promising electron-acceptor moiety for BHJ solar cells.