Effect of Annealing on Exciton Diffusion in a High Performance Small Molecule Organic Photovoltaic Material

[Image: see text] Singlet exciton diffusion was studied in the efficient organic photovoltaic electron donor material DTS(FBTTh(2))(2). Three complementary time-resolved fluorescence measurements were performed: quenching in planar heterojunctions with an electron acceptor, exciton–exciton annihilation, and fluorescence depolarization. The average exciton diffusivity increases upon annealing from 1.6 × 10(–3) to 3.6 × 10(–3) cm(2) s(–1), resulting in an enhancement of the mean two-dimensional exciton diffusion length (L(D) = (4Dτ)(1/2)) from 15 to 27 nm. About 30% of the excitons get trapped very quickly in as-cast films. The high exciton diffusion coefficient of the material leads to it being able to harvest excitons efficiently from large donor domains in bulk heterojunctions.