Interfacial width and phase equilibrium in polymer-fullerene thin-films

DOI: 10.1038/s42005-019-0211-z

Authors: E. L. Hynes (Swansea University) , J. T. Cabral (Imperial College London) , A. J. Parnell (The University of Sheffield) , P. Gutfreund (Institut Laue-Langevin) , R. J. L. Welbourn (ISIS Pulsed Neutron and Muon Source) , A. D. F. Dunbar (The University of Sheffield) , D. Môn (Swansea University) , A. M. Higgins (Swansea University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Communications Physics , VOL 2

State: Published (Approved)
Published: September 2019
Diamond Proposal Number(s): 15486

Abstract: Domain composition and interfacial structure are critical factors in organic photovoltaic performance. Here, we report neutron reflectivity, grazing-incidence X-ray diffraction and atomic force microscopy measurements of polymer/fullerene thin-films to test a hypothesis that these partially miscible blends rapidly develop composition profiles consisting of co-existing phases in liquid-liquid equilibrium. We study a range of polymer molecular weights between 2 and 300 kg mol−1, annealing temperatures between 120 and 170 oC, and timescales up to 10 min, yielding over 50 distinct measurement conditions. Model bilayers of fullerene-derivatives and polystyrene enable a rigorous examination of theoretical predictions of the effect of polymer mass and interaction parameter on the compositions, ϕ, and interfacial width, w, of the coexistent phases. We independently measure ϕ and w and find that both Flory-Huggins mean-field-theory and key aspects of self-consistent-field-theory are remarkably consistent with experiment. Our findings pave the way for predictive composition and interface design in organic photovoltaics based on simple experimental measurements and equilibrium thermodynamic theory.

Journal Keywords: Carbon nanotubes and fullerenes; Electronic devices; Polymers; Surfaces, interfaces and thin films; Thermodynamics

Diamond Keywords: Photovoltaics; Semiconductors

Subject Areas: Physics, Energy


Instruments: I07-Surface & interface diffraction

Added On: 08/10/2019 11:39

Documents:
s42005-019-0211-z.pdf

Discipline Tags:

Surfaces Earth Sciences & Environment Sustainable Energy Systems Energy Physics Climate Change Energy Materials Materials Science interfaces and thin films Polymer Science

Technical Tags:

Diffraction Grazing Incidence X-ray Diffraction (GIXD)