title: Development of the morphology during functional stack build-up of P3HT:PCBM bulk heterojunction solar cells with inverted geometry.
abstract: Highly efficient poly(3-hexylthiophene-2,5-diyl) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells are achieved by using an inverted geometry. The development of the morphology is investigated as a function of the multilayer stack assembling during the inverted solar cell preparation. Atomic force microscopy is used to reveal the surface morphology of each stack, and the inner structure is probed with grazing incidence small-angle X-ray scattering. It is found that the smallest domain size of P3HT is introduced by replicating the fluorine-doped tin oxide structure underneath. The structure sizes of the P3HT:PCBM active layer are further optimized after thermal annealing. Compared to devices with standard geometry, the P3HT:PCBM layer in the inverted solar cells shows smaller domain sizes, which are much closer to the exciton diffusion length in the polymer. The decrease in domain sizes is identified as the main reason for the improvement of the device performance.
authors.affiliation: Technische Universität München , Physik-Department, Lehrstuhl für Funktionelle Materialien, James-Franck-Straße 1, 85748 Garching, Germany.
authors.forename: Weijia
authors.initials: W
authors.lastname: Wang
authors.forename: Stephan
authors.initials: S
authors.lastname: Pröller
authors.forename: Martin A
authors.initials: MA
authors.lastname: Niedermeier
authors.forename: Volker
authors.initials: V
authors.lastname: Körstgens
authors.forename: Martine
authors.initials: M
authors.lastname: Philipp
authors.forename: Bo
authors.initials: B
authors.lastname: Su
authors.forename: Daniel
authors.initials: D
authors.lastname: Moseguí González
authors.forename: Shun
authors.initials: S
authors.lastname: Yu
authors.forename: Stephan V
authors.initials: SV
authors.lastname: Roth
authors.forename: Peter
authors.initials: P
authors.lastname: Müller-Buschbaum
keywords: BHJ solar cell; GISAXS; P3HT:PCBM; inverted solar cell; morphology