Structure property relationship for carbazole and benzothiadiazole based conjugated polymers

• Structure–property effected by D and A blocks.
• Intramolecular charge transfer peak bands shift remarkably.
• Energy level substantially changed.
• Morphology controlled by molecular structure.
• Donor-accept blocks lengthen towards two directions.

A series of conjugated polymers with carbazole monomer/dimer/trimer as the donor unit or benzothiadiazole monomer/trimer as the acceptor unit were synthesized and used as donor materials for polymer solar cells (PSCs). The influence of polymer structure on the optical properties and performance of PSCs was investigated in detail. P1 showed a power conversion efficiency (PCE) of 5.8%. The incorporation of longer donor or acceptor unit leads to a blue shift of absorption spectrum and the polymers became more amorphous due to the large torsion angels in the polymer backbone. After increasing the length of donor or acceptor, the PCE decreased dramatically to 0.43% for P2, 0.23% for P3, and 1.23% for P4. Our results have offered a useful insight to structure–property relationship for high performance polymer solar cells.

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