The Impact of Illumination on the Photoluminescence and Depth Profile of MEH-PPV/dPS Thin Films

This study examines the changes in photoluminescence and film structure due to white light exposure during annealing of conjugated polymer blend thin films. Previous studies in our group have shown that annealing similar polymer blend thin films above the polymers’ T_g in a dark or illuminated environment alters the film structure. These structural changes also impact the photoluminescence (PL) activity of the film. The present work investigates the correlation between light exposure, film morphology and photoluminescence for four films, blends of MEH-PPV and polystyrene at 5, 20, 35, and 50% MEH-PPV. The measured PL of the films showed variation in PL activity dependent on illumination during annealing at 125 °C. Samples that are exposed to light during annealing exhibited lower PL. Time-of-Flight Secondary Ion Mass Spectroscopy provides data to correlate the film’s depth profile to the observed PL. Concurrently, small angle neutron scattering investigates the morphological changes in these films with illumination. These studies indicate that layering of the film dominates the changes in PL activity at low loadings of MEH-PPV, while at higher loadings in-plane morphological changes direct the observed PL.