Modulation of phase separation between spherical and rodlike molecules using geometric surfactancy.

Area of Science:

• Materials Science
• Polymer Chemistry
• Organic Electronics

Background:

• Organic photovoltaic (OPV) blends require controlled phase separation for optimal performance.
• Fullerene derivatives like PCBM are common electron acceptors, often blended with donor polymers like OFTB.
• Achieving stable, nanostructured morphology is crucial for efficient charge separation and transport.

Purpose of the Study:

• To synthesize a C(60)-oligomer dyad to modulate phase separation in OFTB:PCBM blends.
• To investigate the morphological evolution of OFTB:Dyad:PCBM blends using various characterization techniques.
• To explore the potential of the dyad to induce microemulsion-like structures and geometric surfactancy.

Main Methods:

• Synthesis of a C(60)-oligomer dyad with a propylene spacer.
• Differential scanning calorimetry (DSC) for thermal analysis.
• Hot-stage polarizing optical microscopy (POM) for visual observation of phase changes.
• X-ray diffraction (XRD) to analyze crystalline structures.
• Atomic force microscopy (AFM) to probe surface morphology and phase separation.

Main Results:

• A 1:1 blend of OFTB and PCBM formed a eutectic mixture upon thermal annealing.
• Annealing an OFTB:Dyad:PCBM (9:2:9 mass ratio) film yielded an amorphous state with phase-separated domains (~30 nm).
• A different ratio (7:6:7) resulted in a compositionally uniform amorphous film after annealing.
• The formation of microdomains in the 9:2:9 blend suggests geometric surfactancy.

Conclusions:

• The synthesized dyad can effectively control phase separation in OFTB:PCBM blends.
• The dyad can induce nanostructured amorphous morphologies, potentially beneficial for OPV devices.
• Geometric surfactancy is proposed as the mechanism for microdomain formation, analogous to traditional surfactant systems.