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Proceedings Paper

Managing BHJ microstructural evolution for long-term photoconversion efficiency (Conference Presentation)
Author(s): Josue Martinez Hardigree; Graham E. Morse; Priti Tiwana; Giulio Mazzotta; Ivan R. Ramirez; Christopher L. Nicklin; Owen R. Lozman; Moritz K. Riede
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Paper Abstract

In this presentation we evaluate the thermal and light-soaking stability of polymer:fullerene bulk heterojunctions (BHJs) based on a donor polymer recently developed by Merck Chemicals. Blade-coated thin films of pure polymer and BHJs incorporating either PC61BM or PC71BM were investigated using atomic force microscopy (AFM), grazing-incidence x-ray diffraction (GIXD), neutron reflectivity (NR), and UV-Visible spectroscopy. The addition of fullerene to the polymer at device-relevant concentrations (25-50% by weight) results in a 7-fold reduction in surface roughness relative to pure polymer films, attributed to a reduction in the pure polymer domain size with increasingly homogeneous polymer:fullerene mixing. Films subjected to accelerated stressing relevant to scalable OPV fabrication—thermal stressing at 120 °C for 1 hour or light-soaking under AM1.5 light for 8 hours—indicate robust stability to stressing, with thin films showing marginal but monotonic increases in roughness with increasing fullerene concentration. Wide-angle GIXD measurements indicate a contraction of 1-4% in features attributed to polymer crystalline domains upon annealing. Comparison of pre-and post-annealed films reveals increased correlation between polymer scattering features in the latter, consistent with improved ordering of the polymer backbone and sidechains. These findings, together with GIXD measurements of full device stacks and accelerated aging measurements of operational cells, support recent reports on the high photoconversion efficiency stability of this polymer BHJ system for highly scalable, long-lifetime OPVs.

Paper Details

Date Published: 7 November 2016
PDF: 1 pages
Proc. SPIE 9942, Organic Photovoltaics XVII, 99420Y (7 November 2016); doi: 10.1117/12.2238167
Show Author Affiliations
Josue Martinez Hardigree, Univ. of Oxford (United Kingdom)
Graham E. Morse, Merck Chemicals Ltd. (United Kingdom)
Priti Tiwana, Merck Chemicals Ltd. (United Kingdom)
Giulio Mazzotta, Univ. of Oxford (United Kingdom)
Ivan R. Ramirez, Univ. of Oxford (United Kingdom)
Christopher L. Nicklin, Diamond Light Source Ltd. (United Kingdom)
Owen R. Lozman, Univ. of Oxford (United Kingdom)
Moritz K. Riede, Univ. of Oxford (United Kingdom)

Published in SPIE Proceedings Vol. 9942:
Organic Photovoltaics XVII
Zakya H. Kafafi; Paul A. Lane; Ifor D. W. Samuel, Editor(s)

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