We measure the homogeneous excitation linewidth of regioregular poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by means of two-dimensional coherent photoluminescence excitation spectroscopy. At a temperature of 8\,K, we find a linewidth that is always $\gtrsim 110$\,meV full-width-at-half-maximum, which is a significant fraction of the total linewidth. It displays a spectral dependence and is minimum near the 0--0 origin peak. We interpret this spectral dependence of the homogeneous excitation linewidth within the context of a weakly coupled aggregate model.
Grégoire, P., Vella, E., Dyson, M. J., Bazán, C. M., Leonelli, R., Stingelin, N., Stavrinou, P. N., Bittner, E. R., & Silva, C. (2017). Excitonic coupling dominates the homogeneous photoluminescence excitation linewidth in semicrystalline polymeric semiconductors. Physical Review B, 95(18), 1-5. . https://doi.org/10.1103/PhysRevB.95.180201