Thin films of photoactive polymer blends

Area of Science:

• Materials Science
• Polymer Science
• Organic Electronics

Background:

• Photoactive blended films are crucial for organic electronic devices.
• Controlling morphology in polymer blends impacts device performance.
• Poly[(1-methoxy)-4-(2-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) and poly(3-hexylthiophene-2,5-diyl) (P3HT) are key conjugated polymers.

Purpose of the Study:

• To investigate the internal morphology of MEH-PPV/P3HT blended films.
• To understand the relationship between film thickness, polymer concentration, and blending ratios.
• To correlate film morphology with potential photovoltaic applications.

Main Methods:

• Spin coating for film preparation with controlled thickness.
• Grazing incidence small angle X-ray scattering (GISAXS) for lateral structure analysis.
• X-ray reflectivity (XRR) and atomic force microscopy (AFM) for interface and wetting layer detection.
• UV/Vis spectroscopy for complementary structural insights.

Main Results:

• A linear relationship was found between film thickness and polymer solution concentration for both homopolymers.
• The smallest lateral separation between polymer domains, indicating maximum interfacial contact, occurred at a critical blending ratio.
• Wetting layers were detected at the polymer interfaces using XRR and AFM.

Conclusions:

• Controlled film thickness and morphology can be achieved by adjusting polymer solution concentration and blending ratios.
• The identified optimal blending ratio and detected wetting layers suggest promising properties for photovoltaic applications.
• The study provides a foundation for designing high-performance organic electronic devices based on MEH-PPV/P3HT blends.