Probing polaron excitation spectra in organic semiconductors by   photoinduced-absorption-detected two-dimensional coherent spectroscopy
  We report a theoretical description and experimental implementation of a novel two-dimensional coherent excitation spectroscopy based on quasi-steady-state photoinduced absorption measurement of a long-lived nonlinear population. We have studied a semiconductor-polymer:fullerene-derivative distributed heterostructure by measuring the 2D excitation spectrum by means of photoluminescence, photocurrent and photoinduced absorption from metastable polaronic products. We conclude that the photoinduced absorption probe is a viable and valuable probe in this family of 2D coherent spectroscopies. 
Hao Li and Aurelie Gauthier-Houle and Pascal Gregoire and Elenora   Vella and Carlos Silva-Acuna and Eric R Bittner
cond-mat.mtrl-sci