Optimizing stability through conformational locking and ring fusion modulation in organic semiconductors†

The newly synthesized fused tetrathienophenanthroline (TTP) acceptor molecule, achieved via one-pot superacid catalyzed intramolecular cyclization, offers a promising alternative to the conventional benzodithiophene-4,8-dione (BDD) moieties in high-performance photovoltaic materials. The S, N heteroacene type TTP core exhibits complete planarity and enhanced electron richness compared to the BDD core, paving the way for fine tuning the morphology, optoelectronic properties, and frontier molecular energy levels in donor–acceptor-type materials. Side-chain engineering resulted in a balanced electron-rich nature of the monomer and enhanced solubility/processability of the resulting polymers. These molecular strategies for PTTP1-BDT contribute to improved stability and morphology, crucial for organic electronic device applications. Incorporation of PTTP1-BDT and PBDB-T as donor polymers in organic photovoltaics resulted in a power conversion efficiency (PCE) of ∼3% for PTTP1-BDT and ∼8% for PBDB-T. The compromise in PTTP1-BDT based device efficiency was attributed to lower and unbalanced charge mobility.