Electronic structure and surface morphology of [6,6]-phenyl-C71-butyric acid methyl ester films

We investigate the electronic structure of [6,6]-phenyl-C-71-butyric acid methyl ester (PC70BM) films by ultraviolet photoelectron and inverse photoemission spectroscopy. We discuss the electronic structure of PC70BM in comparison with C-70 and [6,6]-phenyl-C-61-butyric acid methyl ester (PC60BM). The molecular orbitals around the energy gap of PC70BM are broadly distributed due to the low symmetry of the molecular structure. Consequently, the energy gap of PC70BM is smaller than that of C-70 and PC60BM. The film deposition method affects the polarization energy between the PC70BM molecules, and thus affects the electronic structure of the films. (C) 2013 Elsevier B.V. All rights reserved.