Electron-hole interaction energy in the organic molecular semiconductor PTCDA

We have used photoemission, inverse photoemission and electron energy loss spectroscopies to determine the on-site attractive electron-hole interaction energy Ee-h in the organic molecular semiconductor 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). Ec-h is found to be 1.0+/-0.2 eV, larger than the PTCDA band width estimated to be smaller than 0.4 eV. Correlation effects in PTCDA are therefore important, consistent with the molecular nature of the solid, They are smaller than in purely molecular solids like C-60 due to the strong pi-electron coupling between overlapping molecules in the molecular stacks. (C) 1997 Elsevier Science B.V.