Fluorinated Polymer Achieves 14.8% Efficiency in Single-Component Organic Solar Cells

Bulk heterojunction organic solar cells have reached high efficiencies but experience morphological instability from phase separation during extended operation. Single-component organic solar cells based on double-cable polymers address this by covalently linking donor and acceptor units within the same polymer chain.

Earlier versions of these single-component devices had been limited by inefficient charge generation linked to highly intermixed morphologies. The fluorinated polymer DCPY2-F improves upon the earlier DCPY2 version. Ultrafast pump-probe transient absorption spectroscopy showed that fluorination accelerates both interfacial charge transfer and long-range charge separation dynamics.

Pump-push-probe transient absorption spectroscopy and steady-state electroluminescence measurements indicated that the faster interfacial charge transfer results from a reduced reorganization energy, which shortens the molecular reorganization time from 2.5 picoseconds to 0.8 picoseconds.

Despite similar acceptor aggregate sizes between the two polymers, DCPY2-F exhibited faster long-range charge separation. Researchers attributed this to a narrower energetic distribution of charge transfer states.

Molecular dynamics simulations revealed that fluorination strengthens non-covalent interactions, leading to better-aligned intermolecular donor-acceptor interfaces. These ordered interfacial charge transfer states support ultrafast and efficient charge generation. The same fluorination approach also improved charge-transfer dynamics and photocurrent in corresponding binary blend devices.