title: X-Ray Nanoscopy of a Bulk Heterojunction.
abstract: Optimizing the morphology of bulk heterojunctions is known to significantly improve the photovoltaic performance of organic solar cells, but available quantitative imaging techniques are few and have severe limitations. We demonstrate X-ray ptychographic coherent diffractive imaging applied to all-organic blends. Specifically, the phase-separated morphology in bulk heterojunction photoactive layers for organic solar cells, prepared from a 50:50 blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) and thermally treated for different annealing times is imaged to high resolution. Moreover, using a fast-scanning calorimetry chip setup, the nano-morphological changes caused by repeated thermal annealing applied to the same sample could be monitored. X-ray ptychography resolves to better than 100 nm the phase-segregated domains of electron donor and electron acceptor materials over a large field of view within the active layers. The quantitative phase contrast images further allow us to estimate the local volume fraction of PCBM across the photovoltaically active layers. The volume fraction gradient for different regions provides insight on the PCBM diffusion across the depletion zone surrounding PCBM aggregates. Phase contrast X-ray microscopy is under rapid development, and the results presented here are promising for future studies of organic-organic blends, also under in situ conditions, e.g., for monitoring the structural stability during UV-Vis irradiation.
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway.
authors.forename: Nilesh
authors.identifier: http://orcid.org/0000-0002-5130-689X
authors.initials: N
authors.lastname: Patil
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway.
authors.forename: Eirik Torbjørn Bakken
authors.initials: ET
authors.lastname: Skjønsfjell
authors.affiliation: Physical Chemistry and Polymer Science (FYSC), Vrije Universiteit Brussel, 1050, Brussels, Belgium.
authors.forename: Niko
authors.initials: N
authors.lastname: Van den Brande
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway.
authors.forename: Elvia Anabela
authors.initials: EA
authors.lastname: Chavez Panduro
authors.affiliation: Physical Chemistry and Polymer Science (FYSC), Vrije Universiteit Brussel, 1050, Brussels, Belgium.
authors.forename: Raf
authors.initials: R
authors.lastname: Claessens
authors.affiliation: Paul Scherrer Institut, 5232, Villigen PSI, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Guizar-Sicairos
authors.affiliation: Physical Chemistry and Polymer Science (FYSC), Vrije Universiteit Brussel, 1050, Brussels, Belgium.
authors.forename: Bruno
authors.initials: B
authors.lastname: Van Mele
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), 7491, Trondheim, Norway.|Department of Micro- and Nanosystem Technology (IMST), University College of Southeast Norway, Campus Vestfold, 3184, Borre, Norway.
authors.forename: Dag Werner
authors.initials: DW
authors.lastname: Breiby
mesh_terms: D004058:Diffusion; D011211:Electric Power Supplies; D037741:Fullerenes / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods*; D012993:Solar Energy; D013876:Thiophenes / Q000737:chemistry; D014961:X-Ray Diffraction / Q000379:methods*; D014965:X-Rays
chemical_list: C539575:(6,6)-phenyl C61-butyric acid methyl ester; D037741:Fullerenes; D013876:Thiophenes; C507295:poly(3-hexylthiophene)