Electroabsorption due to excitons in crystalline molecular thin films grown by organic molecular beam deposition

We measure the electroabsorption due to the lowest absorption peak in ordered organic molecular crystalline films of 3,4,9,10-perylenetetracarboxylic dianhydride grown by organic molecular beam deposition. The application of electric fields induces both a Stark shift and a broadening of the exciton absorption line. We find a nearly spherical exciton of radius 14 ± 2 Å, an effective hole mass of (0.13 ± 0.02)m0, where m0 is the free electron mass, and a binding energy of −150 ± 15 meV, suggesting that excitons in organic crystals with very small intermolecular stacking distances can be described by a combined Wannier and charge-transfer model.