Band-gap and correlation effects in the organic semiconductor Alq3 -: art. no. 033204

We present a spectroscopic study of the electronic properties of a molecular organic semiconductor Alq(3), and its potassium intercalation compound KAlq(3). It is argued that both compounds are strongly correlated materials with a band gap that is to a large extent determined by electron correlation effects. In particular, the Coulomb repulsion energy for two electrons on an Alq(3) molecule in the solids is about 1.4 eV that renders KAlq(3) a Mott-Hubbard insulator and causes a large exciton binding energy in solid Alq(3). The implications of these results for organic devices are discussed.