Combining Fullerenes and Zwitterions in Non-Conjugated Polymer Interlayers to Raise Solar Cell Efficiency

Polymer zwitterions were synthesized by nucleophilic ring-opening of 3,3'-(but-2-ene-1,4-diyl)bis(1,2-oxathiolane 2,2-dioxide) (a bis-sultone) with functional perylene diimide (PDI) or fullerene monomers. Integration of these polymers into solar cell devices as cathode interlayers boosted efficiencies of fullerene-based organic photovoltaics (OPVs) from 2.75 % to 10.74 %, and of non-fullerene-based OPVs from 4.25 % to 10.10 %, demonstrating the versatility of these interlayer materials in OPVs. The fullerene-containing polymer zwitterion (C₆₀ -PZ) showed a higher interfacial dipole (Δ) value and electron mobility than its PDI counterpart (PDI-PZ), affording solar cells with high efficiency. The power of PDI-PZ and C₆₀ -PZ to improve electron injection and extraction processes when positioned between metal electrodes and organic semiconductors highlights their promise to overcome energy barriers at the hard-soft materials interface of organic electronics.