Morphology and Optical Properties of P3HT:MEH-CN-PPV Blend Films

Thin photoactive polymer blend films of poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly(5-(2-(ethylhexyloxy)-2-methoxycyanoterephthalyliden) (MEH-CN-PPV) are investigated. The morphology is probed as a function of blend ratio (21, 28, 44, 54, and 70 wt % P3HT) and annealing using imaging techniques and soft X-ray scattering. The surface structure is detected with optical microscopy and atomic force microscopy (AFM), the inner film morphology and the near-surface structure with grazing incidence resonant soft X-ray scattering (GI-RSoXS) using different X-ray energies. Characteristic lateral structures determined with GI-RSoXS are in agreement with AFM observations and complemented with optical microscopy. The topography and the inner film morphology have the same structural length scales. Grazing incidence wide-angle X-ray scattering (GIWAXS) results confirm the crystallinity of the P3HT domains, which is increasing with annealing, and shows no indication for crystallinity in MEH-CN-PPV. In addition, GIWAXS measurements reveal a blend ratio dependent orientation of P3HT crystals. Absorption and photoluminescence measurements complement the structural investigations.