Excitons in organic semiconductors

The exciton binding energy (Eb) is one of the heavily debated issues in conjugated polymer literature. Most of the experimental studies suggest values around 0.3–0.4 eV for PPV. On the other hand, binding energies ranging from 0.06 eV to more than 1 eV have been reported as well. Time Dependent Density Functional Theory (TDDFT) is employed to calculate Eb for PPV and polythiophenes and their derivatives in order to (i) to clarify the controversial debate of the magnitude of the exciton in PPV and (ii) to study the influence of the substituents on the exciton binding energy of conjugated polymers.