Temperature Dependence of Exciton Diffusion in Conjugated Polymers

• Published in: The journal of physical chemistry. B Vol. 112; no. 37; pp. 11601 - 11604
• Main Authors: Mikhnenko, O. V, Cordella, F, Sieval, A. B, Hummelen, J. C, Blom, P. W. M, Loi, M. A
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18.09.2008
• Subjects: B: Macromolecules, Soft Matter
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp8042363

The temperature dependence of the exciton dynamics in a conjugated polymer is studied using time-resolved spectroscopy. Photoluminescence decays were measured in heterostructured samples containing a sharp polymer−fullerene interface, which acts as an exciton quenching wall. Using a 1D diffusion model, the exciton diffusion length and diffusion coefficient were extracted in the temperature range of 4−293 K. The exciton dynamics reveal two temperature regimes: in the range of 4−150 K, the exciton diffusion length (coefficient) of ∼3 nm (∼1.5 × 10−4 cm2/s) is nearly temperature independent. Increasing the temperature up to 293 K leads to a gradual growth up to 4.5 nm (∼3.2 × 10−4 cm2/s). This demonstrates that exciton diffusion in conjugated polymers is governed by two processes: an initial downhill migration toward lower energy states in the inhomogenously broadened density of states, followed by temperature activated hopping. The latter process is switched off below 150 K.