title: Electronic excitations in solution-processed oligothiophene small-molecules for organic solar cells.
abstract: First principles calculations based on density functional theory and many body perturbation theory have been employed to study the optical absorption properties of a newly synthesized oligo-thiophene molecule, with a quaterthiophene central unit, that has been designed for solution-processed bulk-heterojunction solar cells. To this aim we have employed the GW approach to obtain quasiparticle energies as a pre-requisite to solve the Bethe-Salpeter equation for the excitonic Hamiltonian. We show that the experimental absorption spectrum can be explained only by taking into account the inter-molecular transitions among the π-stacked poly-conjugated molecules that are typically obtained in solid-state organic samples.
authors.affiliation: Dipartimento di Scienze di Base e Applicate per l'Ingegneria, Universitá di Roma "La Sapienza," Via A. Scarpa 14-16, 00161 Rome, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Gala
authors.affiliation: Dipartimento di Scienze di Base e Applicate per l'Ingegneria, Universitá di Roma "La Sapienza," Via A. Scarpa 14-16, 00161 Rome, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Mattiello
authors.affiliation: Dipartimento di Ingegneria Elettronica, Universitá di Roma "Tor Vergata," Via del Politecnico 1, 00133 Rome, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Brunetti
authors.affiliation: Dipartimento di Scienze di Base e Applicate per l'Ingegneria, Universitá di Roma "La Sapienza," Via A. Scarpa 14-16, 00161 Rome, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Zollo