Time- and Polarization-Resolved Photoluminescence of Individual Semicrystalline Polythiophene (P3HT) Nanoparticles

We report on a remarkable size and internal structure dependence on time- and polarization-resolved photoluminescence (PL) from individual regioregular rrP3HT (poly-3-(hexylthiophine)) nanoparticles. For the smallest particles (similar to 34 nm) with relatively low crystallinity (40%), the time evolution of polarization contrast is nearly stationary; for intermediate-sized particles (similar to 65 nm), depolarization occurs on a 1-2 ns time scale. The largest and most crystalline particles studied (118 nm, 70%) show a PL depolarization on a time scale of <50 ps. In every time regime, we observe P3HT nanoparticle PL dynamics that are qualitatively different from those of extended films and single-polymer chains, highlighted by intriguing differences in power law dynamics in the PL intensity at long times. This work may support the hypothesis that hierarchical assemblies of conducting polymer nanoparticles could offer a route to higher efficiency in organic photovoltaic systems.