Acceptor dependent polaron recombination dynamics in poly 3-hexyl thiophene: Fullerene composite films

Recombination in poly-3-hexylthiophene (P3HT) blends with five fullerene acceptors was resolved with temperature-dependent transient absorption spectroscopy. Recombination rates were temperature and acceptor dependent with differing timescales originating from acceptor functionalization and fullerene size. Acceptors with increasing numbers of sidechains (bis > mono > C60) or decreasing fullerene size (C60 < C70 < C80) exhibit slower recombination. The recombination kinetics was correlated to average distance between the fullerene cage and donor site with functionalized moieties acting as dielectric shields to hinder recombination. Three commonly used differential models were evaluated to describe the data. The quantitative failure of these models suggests a microscopic approach (e.g., Monte–Carlo) is needed to quantitatively model the dynamics.