title: Quantitative Tomography of Organic Photovoltaic Blends at the Nanoscale.
abstract: The success of semiconducting organic materials has enabled green technologies for electronics, lighting, and photovoltaics. However, when blended together, these materials have also raised novel fundamental questions with respect to electronic, optical, and thermodynamic properties. This is particularly important for organic photovoltaic cells based on the bulk heterojunction. Here, the distribution of nanoscale domains plays a crucial role depending on the specific device structure. Hence, correlation of the aforementioned properties requires 3D nanoscale imaging of materials domains, which are embedded in a multilayer device. Such visualization has so far been elusive due to lack of contrast, insufficient signal, or resolution limits. In this Letter, we introduce spectral scanning transmission electron tomography for reconstruction of entire volume plasmon spectra from rod-shaped specimens. We provide 3D structural correlations and compositional mapping at a resolution of approximately 7 nm within advanced organic photovoltaic tandem cells. Novel insights that are obtained from quantitative 3D analyses reveal that efficiency loss upon thermal annealing can be attributed to subtle, fundamental blend properties. These results are invaluable in guiding the design and optimization of future devices in plastic electronics applications and provide an empirical basis for modeling and simulation of organic solar cells.
authors.affiliation: EMAT-University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Pfannmöller
authors.affiliation: EMAT-University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Heidari
authors.affiliation: Chilworth Technical Centre, Merck Chemicals Ltd. , University Parkway, Southampton SO16 7QD, U.K.
authors.forename: L
authors.initials: L
authors.lastname: Nanson
authors.affiliation: Chilworth Technical Centre, Merck Chemicals Ltd. , University Parkway, Southampton SO16 7QD, U.K.
authors.forename: O R
authors.initials: OR
authors.lastname: Lozman
authors.affiliation: Thin Film Optics Division, CSEM , Tramstrasse 99, CH-4132 Muttenz, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Chrapa
authors.affiliation: Thin Film Optics Division, CSEM , Tramstrasse 99, CH-4132 Muttenz, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Offermans
authors.affiliation: Thin Film Optics Division, CSEM , Tramstrasse 99, CH-4132 Muttenz, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Nisato
authors.affiliation: EMAT-University of Antwerp , Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: Bals
keywords: Organic solar cells; amorphous polymers; electron energy-loss spectroscopy; on-axis tomography; spectral tomography; spectroscopic imaging