title: Molecular design of photoactive acenes for organic photovoltaics.
abstract: Absorption spectra of n-acenes (n from 2 to 6, for naphthalene, anthracene, tetracene, pentacene, and hexacene, respectively) have been calculated using a newly developed code based on time-dependent density-functional theory. Our calculations show that absorption spectra and charge carrier mobility of acenes not only depend on the molecular identity but also on the molecular packing. By designing the interaction between metal substrates and the first layer of acene molecules, they can be packed in a face-to-face fashion instead of the conventional herringbone (face-to-edge) arrangement. Acenes in the cofacial packing would increase the pi-orbital overlap and thus enhance the charge mobility by maximizing electronic coupling between adjacent molecules. Absorption spectra of cofacially packed acenes have a better overlap with the solar spectrum, which allows harvesting more of the solar energy from red photons.
authors.affiliation: Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA. huangl5@rpi.edu
authors.forename: Liping
authors.initials: L
authors.lastname: Huang
authors.forename: Dario
authors.initials: D
authors.lastname: Rocca
authors.forename: Stefano
authors.initials: S
authors.lastname: Baroni
authors.forename: Keith E
authors.initials: KE
authors.lastname: Gubbins
authors.forename: Marco Buongiorno
authors.initials: MB
authors.lastname: Nardelli