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Proceedings Paper

High exciton diffusion coefficients in fused ring electron acceptor films (Conference Presentation)
Author(s): Justin Hodgkiss

Paper Abstract

Modest exciton diffusion lengths dictate the need for nanostructured bulk heterojunctions in organic photovoltaic (OPV) cells, however, this morphology compromises charge collection. Here, we reveal rapid exciton diffusion in films of a fused-ring electron acceptor that, when blended with a donor, already outperforms fullerene-based OPV cells. Temperature-dependent ultrafast exciton annihilation measurements are used to resolve a quasi-activationless exciton diffusion coefficient of at least 2 ×10-2 cm2 / s – substantially exceeding typical organic semiconductors, and consistent with the 20-50 nm domain sizes in optimized blends. Enhanced 3-dimensional diffusion is shown to arise from molecular and packing factors; the rigid planar molecular structure is associated with low reorganization energy, good transition dipole moment alignment, high chromophore density, and low disorder – all enhancing long-range resonant energy transfer. Relieving exciton diffusion constraints has important implications for OPVs; large, ordered, and pure domains enhance charge separation and transport, and suppress recombination, thereby boosting fill factors. Further enhancements to diffusion lengths may even obviate the need for the bulk heterojunction morphology.

Paper Details

Date Published: 10 September 2019
Proc. SPIE 11094, Organic, Hybrid, and Perovskite Photovoltaics XX, 110940P (10 September 2019); doi: 10.1117/12.2538441
Show Author Affiliations
Justin Hodgkiss, Victoria Univ. of Wellington (New Zealand)

Published in SPIE Proceedings Vol. 11094:
Organic, Hybrid, and Perovskite Photovoltaics XX
Zakya H. Kafafi; Paul A. Lane; Kwanghee Lee, Editor(s)

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