title: Influence of interfacial area on exciton separation and polaron recombination in nanostructured bilayer all-polymer solar cells.
abstract: The macroscopic device performance of organic solar cells is governed by interface physics on a nanometer scale. A comb-like bilayer all-polymer morphology featuring a controlled enhancement in donor-acceptor interfacial area is employed as a model system to investigate the fundamental processes of exciton separation and polaron recombination in these devices. The different nanostructures are characterized locally by SEM/AFM, and the buried interdigitating interface of the final device architecture is statistically verified on a large area via advanced grazing incidence X-ray scattering techniques. The results show equally enhanced harvesting of photoexcitons in both donor and acceptor materials directly correlated to the total enhancement of interfacial area. Apart from this beneficial effect, the enhanced interface leads to significantly increased polaron recombination losses both around the open-circuit voltage and maximum power point, which is determined in complement with diode dark current characteristics, impedance spectroscopy, and transient photovoltage measurements. From these findings, it is inferred that a spatially optimized comb-like donor-acceptor nanonetwork alone is not the ideal morphology even though often postulated. Instead, the energetic landscape has to be considered. A perfect morphology for an excitonic solar cell must be spatially and energetically optimized with respect to the donor-acceptor interface.
authors.affiliation: Department of Physics, University of Konstanz , Universitätsstr. 10, 78457 Konstanz, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Pfadler
authors.forename: Mihael
authors.initials: M
authors.lastname: Coric
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Palumbiny
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Jakowetz
authors.forename: Karl-Philipp
authors.initials: KP
authors.lastname: Strunk
authors.forename: James A
authors.initials: JA
authors.lastname: Dorman
authors.forename: Philipp
authors.initials: P
authors.lastname: Ehrenreich
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.forename: Alexander
authors.initials: A
authors.lastname: Hexemer
authors.forename: Rui-Qi
authors.initials: RQ
authors.lastname: Png
authors.forename: Peter K H
authors.initials: PK
authors.lastname: Ho
authors.forename: Peter
authors.initials: P
authors.lastname: Müller-Buschbaum
authors.forename: Jonas
authors.initials: J
authors.lastname: Weickert
authors.forename: Lukas
authors.initials: L
authors.lastname: Schmidt-Mende
keywords: X-ray scattering; all-polymer; comb-like morphology; exciton separation; nanoimprint lithography; recombination; soft X-rays