Ultrafast charge generation in a semiconducting polymer studied withTHzemission spectroscopy

We study the ultrafast charge generation in a semiconducting polymer (MEH-PPV) by measuring the radiated $\mathrm{THz}$ field after photoexciting the biased polymer with a femtosecond visible pulse. The subpicosecond temporal characteristics of the emitted wave reflects the ultrafast photoconductivity dynamics and sets an upper limit for charge generation of $200\mathrm{fs}$ following photoexcitation, and reveals the dispersive nature of charge transport in MEH-PPV. A comparison of the fields radiated from MEH-PPV and the well-characterized model semiconductor system $\left(\mathrm{GaAs}\right)$ allows for an accurate estimate of the quantum efficiency for charge generation in the polymer, found to be less than $1\%$. Both observations are consistent with ultrafast charge generation in semiconducting polymers through hot exciton dissociation.