title: Spectral aspects of cavity tuned absorption in organic photovoltaic films.
abstract: Concentration of light and infrared capture are two favored approaches for increasing the power conversion efficiency (PCE) of photovoltaic devices. Using optical transfer matrix formalism, we model the absorption of organic photovoltaic films as a function of active layer thickness and incident wavelength. In our simulations we consider the absorption in the optical cavity formed by the polymer bulk heterojunction active layer (AL) between the aluminum cathode and indium tin oxide (ITO) anode. We find that optical absorption can be finely tuned by adjusting the ITO thickness within a relatively narrow range, thus eliminating the need for a separate optical spacer. We also observe distinct spectral effects due to frequency pulling which results in enhanced long-wavelength absorption. Spectral sculpting can be carried out by cavity design without affecting the open circuit voltage as the spectral shifts are purely optical effects. We have experimentally verified aspects of our modeling and suggest methods to improve device design.
authors.affiliation: Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA. bmv8@case.edu
authors.forename: Brent
authors.initials: B
authors.lastname: Valle
authors.forename: Stephen
authors.initials: S
authors.lastname: Loser
authors.forename: Jonathan W
authors.initials: JW
authors.lastname: Hennek
authors.forename: Vincent
authors.initials: V
authors.lastname: DeGeorge
authors.forename: Courtney
authors.initials: C
authors.lastname: Klosterman
authors.forename: James H
authors.initials: JH
authors.lastname: Andrews
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Singer
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks